Loudness Measurement & Monitoring

Loudness Measurement & Monitoring
Yannick LE DREAU Hello and welcome to this presentation on Loudness Measurement and Monitoring, my name is Mike Waidson and I am an application engineer here at Tektronix. Variations in audio loudness between program materials can lead the viewer to reach for the remote control in order to adjust the volume. This can become frustrating for the viewers, as they continually have to adjust the overall volume of the program. Today’s digital audio systems have a much wider dynamic range and high fidelity audio system allow for the full reproduction of the audio signal to be decoded. This can leads to wider variations between audio programs. Program producer want their program or commercial to stand out from the rest and take full advantage of this wider dynamic range. Therefore broadcasters and program provider need to monitor the audio program and ensure a consistent audio loudness level between programs

Agenda What is Loudness ? Loudness Standards Measurement Method
In this presentation we will discuss what loudness is and the standards that have evolve to provide consistent measurement of Loudness. We will then discuss the measurements methods and standards practices that have been developed for a variety of program material and applications. We will look at how these measurements can be performed on a Tektronix waveform monitor and how to configure the instrument to make these audio loudness measurements. Demonstration Loudness Measurement & Monitoring

What is Loudness? Loudness is a subjective measure
Different people perceive loudness differently Loudness is primarily a psychological correlation of the physical intensity of the audio signal. Different techniques have been used to provide correlation of the overall loudness of the signal. Different filters are used to adjust the models to perceived loudness of the human ear. Necessary to measure perceived Loudness Radio & Television broadcasts Music, Speech & Sound Effects Loudness is a subjective measurement. Different people will perceive loudness differently. For instance what appears loud to a child may not appear loud to an elderly relative. Loudness is primarily a psychological correlation that we make to the physical intensity of the audio signal. A variety of different techniques have been used to model and correlate the overall loudness level of the signal to what people perceive as being loud. Different filters have bee used to characterize and model the perceived loudness of the audio signal by the human hear. Various types of program material will have different perceived loudness. For instance there are different dynamics between radio and television broadcasts and between different types of program such as music or speech or special effects.. Loudness Measurement & Monitoring

Loudness Standards IEC 61672-1 Electroacoustics Sound Level Meters
ITU-R.BS 1770 Algorithms to measure audio program loudness and true-peak audio level ITU –R.BS 1771 Requirements of loudness and true-peak indicating meters ATSC A/85 RP Techniques for Establishing and Maintaining Audio Loudness for Digital Television P/Loud Working Group Gating Measurement Inclusion of LFE From a variety of work on loudness measurement several standards have been developed. Initially the IEC61672 standard developed electroacoustic sound level meters that used an A-weighting filter that had a suitable frequency response to the human ear. This algorithm was complicated to developed in a system and the ITU standards body found that a simpler K weighting filter could be used to measure audio program loudness. This process was standardized in ITU-R.BS 1770 and 1771 that are being widely adopted by a variety of organizations around the world. The ATSC used the ITU standard as the basis for their work on developing techniques for establishing and maintaining loudness for a digital television system. That provides a more practical approach to how broadcasters and program providers can measure loudness for a variety of program material. Additional loudness measurement work is being carried out by the EBU and the work of the P/Loud working group that are currently investigating gating measurements and the inclusion of the Lfe channel. Loudness Measurement & Monitoring

Introduction to the Standard ITU-R BS 1770
ITU-R Monophonic Loudness Measured Leq(RLB) K-weighted means square Low computational complexity of algorithm Leq(RLB) provides best performance of all meters tested Simple energy-based loudness as robust as more complex models Design of Leq(K) algorithm High Pass Filter Summation of energy over time Design of Multi-Channel Loudness algorithm Simple building blocks Scalable from 1 to N The ITU carried out extensive testing to develop the RLB K weighting filter. This filter is less complex than the A-weighting filter and is simpler to implement within an algorithm of a device. This simple energy based loudness measurement is more robust and is a less complex model. The Leq(K) algorithm is based on a hgih pass filter that sums the energy over time. This simple approach allows for multi channel loudness to be made of simple building blocks that are scalable from 1 to many channels.. The lower diagram shows a simple block diagram of a multi-channel loudness measurement. Loudness Measurement & Monitoring

Measuring Loudness Uses RLB Filter Pre Filter
Tektronix 15 April 2017 Measuring Loudness ITU-R.BS 1770 Algorithms for audio programme loudness Uses RLB Filter Simpler to implement It should be noted that BS.1770 ended up NOT incorporating Leq(RLB), BUT Leq(R2LB), now formally known as Leq(K) Pre Filter Accounts acoustic effects of the head The ITU-R.BS 1770 algorithm uses a simpler RLB filter characteristic as shown in the top right diagram which is a simple high pass filter.. A pre filter characteristic is used to account for the acoustic effects of a human head. Typically these two filters the Pre-Filter and RLB filter are combined into one algorithm and are referred to as the K Weighting filter. Loudness Measurement & Monitoring Confidential

True Peak Metering Audio Meters use 4x oversampling
Allows True Peak Measurement Other types of meter may under report audio level. Especially at high frequencies ITU-R BS provides method for measurement of True Peak. Within the ITU 1770 and 1771 a true pe4ak meter is defined. In this process the audio meters are 4 times oversampled in order to calculate a True Peak measurement. You can see from the upper right illustration that if just the audio samples are used by the audio meter then the audio level may not record the maximum peaks of the signal and the audio meter may under report the audio level especially at high frequencies. The ITU 1770/1771 provides methods for measurement of the True Peak levels. The basic system of 4x oversampling is used within the audio meter displays of the Tektronix waveform monitors. AEU February Tektronix Confidential VID-11 Loudness Measurement & Monitoring

Loudness Measurement (LKFS)
Definitions L, C ,R, Ls, Rs & N which is total number of channels y Input signal filtered by pre-filter and RLB weighting curve z Weighted Mean Square level G Channel weighting Pre-filter and RLB weighting curve defined as K-Weighting i i i i The Loudness measurement is defined by this equation defined in the ITU 1770 standard. The channels are defined by the letter (i) which is the total number of channels and can be a single mono channel to stereo two channels or multiple channel audio such as 5.1. N denotes the number of audio channels used in the measurement. Each input signal is filtered by the pre-filter and RLB filter and is denoted by the value yi. The weighted means square of each channel is defined by zi and is multiplied by the Channel weighting as shown in the table. This equation produce an overall loudness measurement. AEU February Tektronix Confidential VID-11 Loudness Measurement & Monitoring

EBU P/Loud Group – Rec 128 9

EBU P/Loud R128 The following slides draw heavily from EBU Technical documents 3341/2/3. There are two ways to achieve loudness normalisation in the home: the actual normalisation of the source itself, so that the programmes are equally loud by design the use of loudness metadata that describe how loud a programme is. Within the EBU R128 loudness levelling the first solution is encouraged due to the advantages: simplicity potential quality gain at the source

EBU P/Loud R128 Definitions: ‘LUFS’ is equivalent to ‘LKFS’ (which is used in ITU-R BS ). An input document to change the nomenclature to ‘LUFS’ (which is compliant with international naming conventions) has been submitted to the ITU. A programme is an individual, self-contained audio-visual or audio-only item to be presented in Radio, Television or other electronic media - this includes commercials, trailers, promos, interstitials and similar items Programme Loudness is the integrated loudness over the duration of a programme Loudness Range (LRA) describes the distribution of loudness within a programme Maximum True Peak Level is the maximum value of the audio signal waveform of a programme in the continuous time domain Loudness Range has been implemented in 8000 series but not currently 6/7000 or Cerify

EBU P/Loud R128 The Recommendations are:
that the descriptors Programme Loudness, Loudness Range and Maximum True Peak Level shall be used to characterise an audio signal; that the Programme Loudness Level shall be normalised to a Target Level of -23 LUFS with a permitted deviation of +/-1 LU for programmes where an exact normalisation to Target Level is not achievable practically (for example live programmes) that the audio signal shall be measured in its entirety, without emphasis on specific elements such as voice, music or sound effects that the measurement shall be made with a loudness meter compliant with both ITU-R BS.1770 and EBU Technical Document 3341

EBU P/Loud R128 Further recommendations: that this measurement shall include a gating method with a relative threshold of 8 LU below the ungated LUFS loudness level as specified in EBU Technical Document 3341 that Loudness Range shall be measured with a meter compliant with EBU Technical Document 3342 that the Maximum Permitted True Peak Level of a programme during production shall be -1 dBTP (dB True Peak), measured with a meter compliant with both ITU-R BS.1770 and EBU Technical Document 3341 that loudness metadata shall be set to indicate -23 LUFS for each programme which has been loudness normalised to the Target Level of -23 LUFS that loudness metadata shall always correctly indicate the actual programme loudness, even if for any reason a programme may not be loudness normalised to -23 LUFS

Measuring Loudness So far we have looked a variety of applications within the broadcast and post production chain and how the ATSC standard provides recommendation for the practical implementation of measure Loudness. In this next section we will take a look at how to configure a waveform monitor to measure loudness.

LKFS Meter & Target Loudness
Audio Meter Scale in LKFS Settings Number of Channels Duration of Average Gating Threshold settings EBU R128 standard -23 LKFS with deviation of +/-1 LKFS User Defined Limits Loudness = log ∑ G . z (LKFS) 10 N i i Too Loud User Defined EBU Target Loudness -23LKFS (+/- 1) User Defined The Loudness meter is based on the ITU 1770 standard based on the Loudness measurement equation that produces a LKFS Loudness K weighted Full Scale value. This measurement is based on the number of audio channels that are included in the summation. Denoted by N within the equation. The measurement can be made over an average duration this duration can be a short period typically ten seconds, within the waveform monitor this period can range from 1 to 60 seconds. The infinite duration measurement is based on the duration of the audio session over which the measurement has been monitored. There are a variety of settings within the Loudness configuration of the loudness meter. For the ATSC standard the Target Loudness is set to -24LKFS with a deviation of +/- 2LKFS and the user or program provider can define upper and lower thresholds for too loud or too quite. Too Quiet User Defined Loudness Measurement & Monitoring

WFM7120 Loudness Configuration
Press Config button Navigate to Loudness Settings Enter sub menu and select Loudness Preset EBU R128 Yellow text indicates changing of settings Within the configuration of the WFM7120 press the Config button to enter the configuration and navigate to the Loudness Settings menu. Within this sub menu there are a variety of settings that can be configured by the user. To simplify operation within the Loudness Presets menu there are a variety of preconfigured settings. Select the EBU R128 settings to load the configurations that are in compliance with this recommended practice. When the preset is loaded the value that are changed by the preset are shown in yellow. Loudness Measurement & Monitoring

WFM7120 Elements of Loudness Monitoring
Loudness Measurements Short Infinite True Peak Dialnorm Run Time Loudness Meter Within the audio tile the loudness meter can be enabled within the audio tile menu. Accessed by pushing and holding the audio tile button. The audio display shows the meter enabled and the Pl beneath the bar indicates that the meter is currently configured to show the program loudness. The loudness measurement in this case is based on the summation of certain audio channel. The green label used for the audio bars indicates that this channel is included within the measurement a label shown in white indicates that this channel is not included in the measurement. A variety of user defined limits can be set up for the loudness meter and we will discuss these in detail in the next slide. At the top right of the display are a variety of measurements and loudness information. That provide loudness measurement values for the Short and Infinite duration, along with the maximum True Peak and Dialnorm values. The run time of the audio session is also included within the audio tile. Program Loudness Green Audio Labels Channels Summed into Loudness Measurement Loudness Measurement & Monitoring

WFM7120 Elements of Loudness Monitoring
Too Loud User Defined EBU R128 -23LKFS (+/- 1) User Defined Too Quiet User Defined The Loudness meter that can be enabled within the audio tile provides a variety of information. The white diamond on the right hand side of the meter indicate the user defined target loudness which is -23LKFS for the EBU standard. A user defined upper and lower range of allowed loudness is shown by the yellow and blue diamonds. For the EBU standard +/-1 loudness units are allowed. The user can also define their own threshold for classification of what they consider Too Loud shown by the red diamond and what is considered Too quiet. In-bar message will also be displayed if gating is being performed by the loudness measurement or if the signal is too Loud, or too Quiet. In-Bar Message LOUD, QUIET, GATED Loudness Measurement & Monitoring

WFM7120 Audio Session Summary of Audio
Clips, Over, Mute, Silence, Peak/ High Level Loudness Measurement Per Channel Per Pair Infinite Loudness Short Loudness Loudness Information Duration of Short Period Channel Used in summation Loud Alarm Run Time of Session The audio session display is where the user can find a summary of the audio measurement performed by the instrument. Summaries of clips, overs, mute and silence present during the session are shown for each channel. Along with the peak and high audio level that have occurred during the session. The loudness measurement are show per channel and for pairs of channels. Along with the overall Infinite and Short loudness measurement, for informational purpose the duration of the short period and the number of channels used within the summation of the measurement are also provided. The Run Time value show how long the session has been running and the session can be manually started stopped or reset by the user. Loudness Measurement & Monitoring

WFM7120 Loudness Session Loudness Chart
Logs Loudness value every second Trend Chart 90 Seconds 180 Seconds Bar Chart 9 minutes to 6 hours Save Loudness value to USB or via network. With the ALOG option on the WFM7120 and WVR series the user can select the Loudness Session that produces a Loudness log either as a trend chart or bar chart. The trend chart show the loudness value every second for a duration window of 90 or 180 seconds. For longer duration a Bar Chart is used to show the minimum and maximum loudness values during each bar. The loudness chart supports from 9 minutes to 6 hours duration. Loudness Measurement & Monitoring

WFM7120 Loudness Session Loudness Chart Bar Chart
From 9 minutes to 6 hours LKFS Short LKFS Infinite Dialnorm True Peak Max / Min Value LKFS Summary Information Channel Summation Short Period Target Loudness Save Loudness Session to USB or via network. Here we can see the Loudness Bar chart showing the maximum and minimum loudness values for each bar period. Below the chart is a variety of information. The current Loudness measurement for both short and infinite values are shown along with the Dialnorm and True Peak values. The maximum and minimum loudness values are reported for the session Along with summary information for channel summation, short period duration and target loudness. The user can save this loudness data to a USB device or via a network connection to the instrument. This allows the user to save the loudness data for further analysis. The data can be easily imported into a spreadsheet application and a variety of charts and reports can be created. Loudness Measurement & Monitoring

WFM7120 Loudness Session Export
Here you can see the original data within the instrument and the values obtained from the exported data within a spreadsheet application. Loudness Measurement & Monitoring

WFM7120 Loudness Session Export
By using a spreadsheet application a graph can be drawn of the data values. This data can then be manipulated in a variety of ways to suit the customers requirements. Here you can see a graph of a complete six hour period. Loudness Measurement & Monitoring

Multichannel Audio & Distribution Systems
In this next section we will discuss Dolby metadata and how this metadata can be added within a facility to support multichannel audio and how the signals are distribution throughout the system.

Dolby Metadata AC-3 Metadata includes 28 parameters Informational
Seven optional parameter No effect on audio decoding Basic Nineteen parameter Dynamic Range, Downmix Optimize the listening experience Critical Required for proper encoding and decoding Channel Mode (acmod) Describes channel format Dialog Level (dialnorm) Sets dialog level Dolby Metadata is carried within the digital data stream and includes 28 different parameters. Some of these parameters are informative and have no effect on audio decoding. There are 19 basic parameters that are provided to optimize the listening experience such as Dynamic Range and Downmix. The are two paramters that are critical and required for proper encoding and decoding of the data stream. Channel mode describes the channel format and Dialog Level also referred to as Dialnorm that set the average dialog level. Within the Tektronix instrument the Dolby Status menu provide information on the Dolby metadata and can be extracted from the audio data stream or via metadata in the vertical ancillary data space that conforms to SMPTE2020. THE AC-3 MULTICHANNEL AUDIO SYSTEM The ATSC AC-3 audio system is intended to deliver a reproduction of the original (unprocessed) content at the output of the AC-3 decoder in a receiver, normalized to a uniform loudness. It provides the ability for broadcasters to allow each listener the freedom to exert some control over the degree of dynamic range reduction, if any, that best suits their listening conditions. The dynamic range processing part of the system is described in Section 9, but its operation is predicated on having properly normalized content delivered to it. The metadata parameter dialnorm is transmitted to the AC-3 decoder along with the encoded audio. The value of the dialnorm parameter indicates the loudness of the Anchor Element of the content. The dialnorm value of a very loud program might be 12, and of a soft one, 27. There is an attenuator at the output of the AC-3 decoder that applies appropriate attenuation to normalize the content loudness to –31 LKFS. If the dialnorm parameter accurately reflects the overall loudness of the content, then listeners will be able to set their “volume” controls to their preferred listening (loudness) level and will not have to change the volume when the audio changes from program to advertisement and back again. If all broadcasters use the system properly, the loudness will also be consistent across channels. METADATA MANAGEMENT CONSIDERATIONS IMPACTING AUDIO LOUDNESS An AC-3 encoder allows the setting of up to 28 metadata parameters concerning the characteristics of the accompanying audio in the bit stream (see Annex G). The parameters can be classified in three groups: Informational metadata, which includes seven optional parameters that can be used to describe the encoded audio. These parameters have no affect on encoding or the decoded listening experience in the home. Basic control metadata, which includes 19 parameters that determine the dynamic range compression, down-mixing, matrix decoding, and filtering used in certain operating modes the professional encoder and consumer decoder. Optimizing the setting of these parameters for each program may enhance the listening experience under varying listening conditions with certain content types. However, default values may be used without detriment to listening experience. Critical control metadata, which includes two parameters that are critical for proper encoding and decoding: • Channel mode (acmod), which should be chosen correctly to engage proper channel formatting in the decoder to match the content. Improper use of this parameter may alter transmission and cause the loss of dialog when encoding a 5.1 program; e.g., encoding 5.1 channel soundtrack with 2/0 metadata. • Dialog level (dialnorm), which A/53 requires to be set correctly to prevent (potentially severe) loudness variation during content transitions on a channel and when channel changing across the DTV dial. Incorrect dialnorm values can lead to a variation in loudness as large as 30 dB. Apart from the dialnorm parameter, default values may be used for most of the other metadata parameters with acceptable results. Once mixers and producers become more familiar with these parameters by monitoring using available emulation systems, they can select values that further optimize the presentation of their program content. 7.1 Importance of dialnorm Carriage of and correct setting of the value of dialnorm is mandatory for DTV broadcasting in U.S., see 47 C.F.R. Section (d), incorporating by reference ATSC A/53 Part 5:2007 Section 5.5, “Dialogue Level” [1]. This RP identifies methods to ensure consistent digital television loudness through the proper use of dialnorm metadata for all content, and thus comply with A/53. Many of the principles successful management of dialnorm may also apply to the management of other AC-3 metadata parameters. As indicated in Section 6, minor measurement variations of up to approximately ±2 dB anticipated, and these may lead to minor variations between the value of dialnorm and the actual program loudness. These minor variations are acceptable (due to the comfort zone – see Annex E); however, operators should not intentionally operate at the high or low side of this range. Loudness Measurement & Monitoring

Dolby Metadata Management
Requirements for accurate Metadata Methods Fixed Method AC-3 encoder Dialog Level Is “fixed” to a single value Preset Metadata AC-3 encoder “presets” are programmed, each with different dialnorm Agile Metadata AC-3 encoder is configured to receive external metadata Section 7 of the ATSC standard describes three methods of using audio metadata: Fixed, Preset, or Agile. The Fixed method set the Dialog Level to a single fixed value. The second preset method allows the encoder to be programmed with different dialnorm value based on the preset loaded by the equipment. The Agile method allows the encoder to be configured by receiving external metadata that programs the equipment. Any one of these approaches will deliver consistent loudness to the listeners; the broadcaster is free to use the method that best suits their operational practices. Whichever approach is selected, the system depends on transmitting a value of dialnorm that correctly represents the Dialog Level of the content, which depends in turn on accurate loudness measurements. Metadata Management Modes The requirement for accurate dialnorm, channel mode (acmod), and other metadata can be met in three different ways, at the discretion of the operator: • Fixed metadata: The AC-3 encoder Dialog Level is “fixed” to a single value and the content Dialog Levels are conformed to that setting. • Preset metadata: AC-3 encoder “presets” are programmed, each with different dialnorm values and engaged via a “General Purpose Interface” (GPI) or other control interface. • Agile metadata: The AC-3 encoder is configured to receive external metadata. An upstream “agile” dialnorm metadata system may be used to deliver dynamically changing dialnorm values to the encoder, corresponding to the changing loudness at the content boundaries. When managed properly, all three methods provide a compliant and acceptable end result for the consumer. The majority of the discussion in this section of this RP focuses on the dialnorm parameter. Readers are encouraged to refer to Annex G and to research information on how the remaining metadata parameters may impact coding. It is also possible for the operator to apply a hybrid approach, choosing one of the methods for loudness management and a different method for the remainder of the metadata: e.g., maintaining a fixed dialnorm value but switching channel mode as required. Loudness Measurement & Monitoring

Fixed Metadata Consumer AC-3 Decoder Process, Storage Distribution and Switching Encoder Source 1 Audio Source n ATSC Internal Metadata Values Simply “Fix” AC-3 Encoder dialnorm setting Measure long term loudness and set dialnorm to this value Content Delivery specification should set Target Loudness of ingest material Non-conforming content needs to be measured and offset applied Poses mininal risk to content. Simplifies system requirements Using a fixed dialnorm setting means the long term loudness of the audio program output should be measured and the Dialnorm will be set to this value. The content delivery specification should set the Target Loudness of the ingest of the material and any non-conforming audio needs to be measured an appropriate offsets applied in order to conform to the transmission requirements. This approach poses minimal risk to content and simplifies system requirements. Using Fixed dialnorm Metadata The concept of fixed dialnorm is simply to “fix” the AC-3 encoder dialnorm setting to a single value within a network or broadcast system and to bring the loudness of the encoder audio input signal into conformance with this setting. The operator can choose any dialnorm value from 31 to 1; however, compliance with A/53 requires the operator to employ a value equal to the average dialog loudness of all content. See Figure 7.1. Setting dialnorm by Long-Term Averaging Method An operator can achieve a first-approximation of compliance with A/53 by measuring the longterm average loudness of the station output, and setting the AC-3 encoder dialnorm parameter equal to this value. The averaging period should be chosen to include all types of content. If the Dialog Level of individual pieces of content deviate significantly from that long-term average, the dialnorm parameter will not properly reflect the Dialog Level of that content. This situation should be addressed by the program originator or operator and corrected (see Sections and 7.3.3). This method may not apply to operators using content with intentionally wide dynamic range. Setting dialnorm for Production A content delivery specification should specify the Target Loudness for all content. This establishes the anchor for layering of music and effects for the soundtrack. Loudness should be measured with a meter using the ITU-R BS.1770 recommendation [3] to confirm the average loudness of dialog. The supplier should indicate the actual average loudness with the deliverable. Cooperation between content supplier and recipient is necessary to achieve successful loudness management when implementing this practice. Content Not Conforming to the Target Loudness If the operator needs to make use of content not conforming to the established Target Loudness value, an offsetting gain or loss will need to be inserted to compensate. If the difference is unknown, it will be necessary to measure the content loudness before compensation is applied. dialnorm and Loudness Quality Control To ensure the proper match between dialnorm value and loudness, the operator should make use of loudness metering during quality control, and when necessary make compensating adjustments to ensure the loudness meets the target value. Emission dialnorm Setting for Compliance with A/53 An operator receiving content that is delivered at a fixed loudness, where there is no gain adjustment or processing after the receiver, should set the value of dialnorm in the emission AC-3 encoder to match the originator’s specified loudness (often specified in contract, signal specification document, etc.). If a fixed gain or loss is applied in the signal chain, the AC-3 encoder dialnorm value should be offset accordingly from the originator’s loudness. For example, if the originator delivers audio with a loudness of –24 LKFS and no gain or loss is incurred in the chain, dialnorm would be set at 244. However, if a gain of 3 dB is added, corresponding to a loudness of –21 LKFS, dialnorm would be set to 21. If instead a loss of 2 dB is introduced, corresponding to a loudness of –26 LKFS, dialnorm would be set to 26. If an audio loudness processor is utilized, the AC-3 encoder dialnorm value should be set to the Dialog Level at the output of the audio processor. Fixed dialnorm Advantage A fixed dialnorm system poses minimal risk to the content. Fixed dialnorm has the advantage of simplicity, with no requirement for additional metadata equipment or data management. This approach can be used with every AC-3 encoder and is the only approach possible when using an encoder without metadata input or external GPI control. Loudness Measurement & Monitoring

Preset Metadata Consumer AC-3 Decoder Process, Storage Distribution and Switching Encoder Source 1 Audio Source n ATSC Internal Metadata Values External Control Auto- mation Change between preset metadata values via external control Preset are loaded into AC-3 encoder based on known differences in content loudness Automation system used to recall presets based on content and channel modes AC-3 Framesync some encoders disrupt audio bit stream when preset is changed. Another approach is to change between various presets that are loaded within the AC-3 encoder and use an external device to trigger these changes. Various preset are loaded within the AC-3 encoder based on known differences in content loudness. An automation system is then used to recall these preset based on content and channel modes. Care has to be taken in ensuring correct frame sync as some encoders can disrupt the audio nit stream when a preset change is made. This will result in an audible glitch to the transmission output. This mode is often used when changes have to be made between stereo and multi-channel audio programs. Using Preset dialnorm Metadata If the operator needs to accommodate a small number of discrete changes to the dialnorm value or other metadata parameters, some AC-3 encoding systems can be configured to change between preset metadata values via external control; e.g., with a contact closure to a GPI. This method requires GPI external triggers for accurate preset signaling from the automation playlist or switcher. It is often used to switch between stereo and 5.1 encoding modes, even when the dialnorm remains fixed at a single value. See Figure 7.2. Implementation The implementation of preset metadata is similar to “fixed” metadata. Predetermined preset values are loaded into the AC-3 encoder to accommodate known differences in content loudness. Compliance with A/53 then requires that content be delivered with loudness matching one of the preset values, and that the automation system be programmed to change presets according to different content loudness values and channel modes. AC-3 Framesync Requirement Some AC-3 encoders reset and disrupt the audio bit stream output when a preset is changed, Based on the type of ATSC encoder being used, this may result in an audible “glitch” on air. To avoid this potential problem, it may be necessary to provide an AC-3 framesync for the output of the AC-3 encoder to stabilize the AC-3 source for the ATSC encoder. Loudness Measurement & Monitoring

Agile Metadata Setting different dialnorm values for different content
Consumer AC-3 Decoder Process, Storage Distribution and Switching Source 1 Audio Source n ATSC Encoder Internal Metadata Values De- Embed Meta- Data Setting different dialnorm values for different content Embed the metadata parameters within the SDI ANC data De-Embed metadata just prior to AC-3 Encoder Dialnorm settings change appropriately on boundaries of content Needs to be employed throughout the whole system An agile metadata system involves setting a different dialnorm value for each piece of contnent. The metadata is extracted at the input of the system and placed within the SDI Ancillary data space in conformance with SMPTE 2020. This metadata is then carried with the material throughout the broadcast chain. Just prior to AC-3 encoding the metadata is de-embedded from the SDI signal and applied to the encoder. Allowing dialnorm settings to change appropriately on boundaries of content. This approach requires that this system be employed throughout the facility. Loudness Measurement & Monitoring

Agile Metadata Complex System
Requires full Loudness measurement of each piece of content Loss of metadata could result in an audio discrepancy AC-3 encoder will revert to units metadata settings Requires an agile infrastructure throughout Broadcast plant Equipment deployed at all input, output and monitoring locations Agile systems provide the greatest flexibility for the content provider Does not impose creative limitations An agile system is the most complex and required full loudness measurement of each piece of material. An agile infrastructure is required throughout the broadcast plant and equipment must be deployed at all input and output monitoring locations. There is the potential for the loss of metadata that could result in audio discrepancy. If the metadata is removed from the signal or additional SMPTE 2020 packets are added to the SDI signal. An Agile infrastructure is required throughout the broadcast plant if this method is to be deployed. Equipment is needed at all input and output monitoring locations in order to embed and extract the metadata and to monitor for conformance of the signal. An agile system provide the most flexibilty for the content provider as is does not impose creative limits on the program material. Using Agile dialnorm Metadata An agile metadata system allows setting different dialnorm values for different content that has different loudness. This is accomplished by embedding the dialnorm parameter within the metadata bit stream accompanying the content at an “upstream” location. The metadata is dis-embedded just prior to the AC-3 encoder and connected to its external serial metadata input. The dialnorm setting changes appropriately on boundaries of the content. See Figure 7.3. 7.5.1 System Deployment When the agile metadata approach is used by a network operator, it will need to be employed throughout the plant of every broadcast station or MVPD head-end that receives content from the network. This requires deployment of complex encoding and decoding equipment at all input, output, monitoring, and processing points in the distribution chain, from the metadata origin through to all AC-3 encoders. It is essential that the agile metadata reach the AC-3 encoder. Several approaches for agile metadata delivery and storage are available, and can be used separately or in combination— the AC-3 metadata (as discussed in Annex G) is a consumer subset of Dolby E metadata, as described in SMPTE RDD 6 [22]. This may be transported over serial data links, as vertical ancillary (VANC) data, or as data carried in compressed bitstreams. It may also be stored in file-based systems. Dolby E Metadata Over Serial Link Dolby E metadata in its baseband form may be carried via serial links. This approach may require a dedicated serial layer that remains carefully time aligned to the audio and video signals. specification, the Target Loudness is either carried in the encoded signal by the value of the dialnorm parameter or communicated to the distributor for subsequent encoding. Insertion in the deliverable can be accomplished through a dubbing process or by making use of the pre-read feature available in some video tape recorders. See Figure 7.4. Dolby E Metadata in VANC Dolby E metadata can also be embedded within the VANC of standard- or high-definition serial digital systems and extracted downstream using the SMPTE 2020 [8] standard. This approach may require multiplexers and de-multiplexers, and requires support by video storage, encoding, processing, and distribution equipment with the ability to pass the VANC signal intact. Some storage devices have limited or no VANC capability. Metadata and Codecs Certain systems used for backhaul, distribution, and storage applications also have the ability tocarry Dolby E metadata. These systems include the Dolby E compressed bitstream itself, and proprietary5 formats which require specialized audio encoders and decoders. They also may require equipment that can offset video timing to compensate for the encoding and decoding latency introduced. Most professional digital video equipment can be configured to pass these encoded signals through standard digital audio channels that comply with SMPTE 337 [23]. File-based Metadata There are a large number of file-based techniques for storing Dolby E metadata, some of them standardized and some of them proprietary. These are outside the scope of this document. 7.5.2 Production Technique – Live In live production using an agile metadata approach, the television production mix engineer selects a specific but arbitrary loudness target for each program, with considerations for dynamic range, headroom, and the type and mood of the program. This parameter establishes the loudness anchor for layering of music and effects for the soundtrack. Depending on the deliverable specification, the Target Loudness is either carried in the encoded signal by the value of the dialnorm parameter or communicated to the distributor for subsequent encoding. 7.5.3 Production Technique – Non-Real-Time With post-produced content using the agile metadata approach, the final mix loudness is determined either during program production or after it is complete. Depending on the deliverable 7.5.4 Production Monitoring The soundtrack should be measured using the ITU-R BS.1770 recommendation [3] to confirm that the average loudness for the entire length of the production matches the chosen dialnorm value. (See Section 5.) 7.5.5 Semi-Agile Metadata An operator may use an agile metadata system but choose to simplify metadata authoring and insertion operations by specifying fixed Target Loudness values to be used by content providers. 7.5.6 Impact of Metadata Loss on Content A risk associated with the use of an agile metadata system is the potential for a severe discrepancy in loudness between programs and between stations if metadata is lost. All AC-3 encoders with external metadata input provide a “reversion” feature to mitigate the impact of metadata loss. With this feature, the encoder can be configured to either retain the most recent metadata value or revert to an operator-defined preset. While this feature can minimize the impact upon the consumer, the error in loudness or other metadata parameters (such as channel mode) can still be significant. The reversion parameter should be chosen to minimize the impact of metadata loss on the presented content. 7.5.7 Fixed-Agile Hybrid In some instances, an operator may choose to intentionally use the reversion feature accommodate content without metadata. It is critical that operators choose appropriate settings for all metadata parameters of the reversion preset, particularly ensuring that the loudness of the distributed content without metadata matches the pre-determined reversion dialnorm parameter. Reversion may also be used to protect against a loss of metadata recognizing that the reversion metadata parameters may not exactly match that of the content. In the event of a metadata loss, all content being encoded under reversion will be subject to these parameters. It is especially critical that channel mode be set in fashion to protect all content under any circumstance. The inadvertent use of 2/0 channel mode with 5.1 content will eliminate channls 3 – 6 of the encoded audio and put the content at risk. Advantages of Agile Metadata An agile system presents the most flexibility for the content provider without imposing creative limitations. Loudness Measurement & Monitoring

Fixed Agile Hybrid Broadcast Example IRD MUX Live productions
L-Band ASI VANC Inserter HD-SDI Dolby E MUX IRD Ch 1/2 L/R Ch 3/4 C/Lfe Ch 5/6 Ls/Rs Ch 7/8 Lt/Rt Decoder To Facility HD Router With SMPTE 2020 BB Reference Broadcast Example Live productions Metadata delivered via Dolby E Broadcast Center infrastructure Metadata extracted from Dolby E signal Inserted into HDSDI VANC line 9 Routed through plant To Distribution system An agile system is extremely flexible but can be a challenge to implement effectively within a broadcast system. An alternative is to use a hybrid approach that combines the simplicity of the fixed system with the flexibility of the agile system and creating an fixed agile hybrid. In this case the incoming signals are delivered in Dolby E and the metadata is extracted from the Dolby data stream and encoded within the SMPTE2020 standards as vertical ancillary data. Typically inserted into line 9 of an HD-SDI signal and routed throughout the plant till finally the signal is distributed. Fixed-Agile Hybrid In some instances, an operator may choose to intentionally use the reversion feature accommodate content without metadata. It is critical that operators choose appropriate settings for all metadata parameters of the reversion preset, particularly ensuring that the loudness of the distributed content without metadata matches the pre-determined reversion dialnorm parameter. Reversion may also be used to protect against a loss of metadata recognizing that the reversion metadata parameters may not exactly match that of the content. In the event of a metadata loss, all content being encoded under reversion will be subject to these parameters. It is especially critical that channel mode be set in fashion to protect all content under any circumstance. The inadvertent use of 2/0 channel mode with 5.1 content will eliminate channels 3 – 6 of the encoded audio and put the content at risk. Advantages of Agile Metadata An agile system presents the most flexibility for the content provider without imposing creative limitations. Loudness Measurement & Monitoring

Fixed Agile Hybrid – Network Distribution
ASI Fixed Agile Hybrid – Network Distribution HD-SDI Dolby E D E M U X Ch 1/2 L/R Ch 3/4 C/Lfe Ch 5/6 Ls/Rs Ch 7/8 Lt/Rt Encoder With SMPTE 2020 HD Router Master Control VANC Decoder Metadata MPEG BB Ref. Stereo Downmix AES L/tRt Broadcast Center Signal Flow Multiple Sources Signals Routed to Transmission Dolby E encoding Audio Metadata In VANC Metadata Extracted from VANC and delivered to Dolby E encoder Also extracted by transmission encoder Delivered to Network as private MPEG data service At the network distribution center multiple sources are routed and transmitted and during this process the Dolby VANC data is extracted from the SDI signal and applied to the Dolby E encoder. A stereo downmix of the mutli channel audio is also provided. So that the MPEG encoder provides a video stream and various audio data streams for transmission to affiliates. Typically only a limited set of metadata modes are allowed to simplify system implementation. Fixed-Agile Hybrid In some instances, an operator may choose to intentionally use the reversion feature accommodate content without metadata. It is critical that operators choose appropriate settings for all metadata parameters of the reversion preset, particularly ensuring that the loudness of the distributed content without metadata matches the pre-determined reversion dialnorm parameter. Reversion may also be used to protect against a loss of metadata recognizing that the reversion metadata parameters may not exactly match that of the content. In the event of a metadata loss, all content being encoded under reversion will be subject to these parameters. It is especially critical that channel mode be set in fashion to protect all content under any circumstance. The inadvertent use of 2/0 channel mode with 5.1 content will eliminate channels 3 – 6 of the encoded audio and put the content at risk. Advantages of Agile Metadata An agile system presents the most flexibility for the content provider without imposing creative limitations. Loudness Measurement & Monitoring

Effectively control of program-to-interstitial loudness
Fixed dialnorm Ensure all content meets Target Loudness Long term loudness matches dialnorm File based use a scaling device to match long term loudness Real-time loudness processing device to match loudness Agile dialnorm Measure all program content Dialnorm must match actual calculated loudness Filebased set dialnorm to measured loudness of specific content Real-time process to match content specific loudness and set dialnorm based on this loudness value The idea within the fixed or agile systems is to effectively control the loudness between program and interstitial material. Using the fixed dialnorm method operators need to ensure all content meets the Target Loudness and that their long term loudness measurement match the dialnorm value. In the case of file based material a scaling device can be used to match long term loudness automatically. While in real-time a loudness processing device can be used to match loudness. For an agile system all program content needs to have loudness measurements made and the dialnorm value must match the actual calculated loudness. For filebased content the dialnorm should be set based on the specific loudness of the content. Real-time process should be done to match content specific loudness and set dialnorm based on this loudness value. METHODS TO EFFECTIVELY CONTROL PROGRAM-TO-INTERSTITIAL LOUDNESS The ATSC digital television audio system (AC-3), with its expanded dynamic range and new techniques for managing loudness, presents the possibility of undesirable loudness changes at transitions (to and from various pieces of content) if not managed properly. This condition is known to annoy the audience by frequently forcing the listener to adjust the audio levels at transitions to maintain a comfortable volume. This condition can be alleviated when proper DTV loudness management is applied. AC-3 incorporates the necessary technology to mitigate variations in loudness during program-to-interstitial transitions. These techniques are described below: 8.1 Effective Solutions Large loudness variation during transitions can be effectively managed by ensuring dialnorm properly reflects the Dialog Level of all content. 8.1.1 For Operators Using a Fixed dialnorm System (See Section 7.2)  a) Ensure that all content meets the Target Loudness and that long term loudness matches the dialnorm value. b) Employ a file-based scaling device to match long term loudness of non-conformant file based content to the target value. c) Employ a real-time loudness processing device to match the loudness of non-conformant real-time content to the target value. 8.1.2 For Operators Using an Agile dialnorm System (See Section 7.5)  a) Ensure that during program production, post-production, or ingest, content is measured (see Section 5.2) and labeled with the correct dialnorm value matching the actual loudness of the specific content. b) Employ a file-based measurement and authoring device to set dialnorm to the average loudness of the specific content. c) Employ a real-time processing device to match content to a specific loudness. Apply a dialnorm value, matching the loudness of all content processed by this device. Loudness Measurement & Monitoring

Dynamic Range Control DRC calculations based on the indicated loudness
Dialnorm need to accurately reflect loudness Profession Encoding profiles for DRC Music Light Music Standard Film Light Film Standard Speech Dolby Digital (AC-3) modes Line Mode RF Mode DRC – “None” Inhibits Generation of DRC profiles Prevents viewer selection Protection Limiting will not be available Recommend profile other than “None” The Dyanmic Range Control parameters are calculated based on the indicated loudenss. Therefore the dialnorm value needs to accurately reflect the loudness of the audio data. For Dolby E professional encoding there are a range of profiles that can be contained within the metadata. These profiles are compatible with the Dolby Digital dyanmic range parameters for line and RF modes. A Dynamic Range Control of None could be set but this is not recommended as this inhibits the generation of DRC profiles and prevents viewers select of these modes. Additionally there will be no Limit protection available when there is no DRC selected. Dynamic range can be used to limit the overall dynamic range of the audio program by boosting the low audio levels and cutting the upper audio levels so that the viewer can listening at a comfortable level. by the dialnorm metadata parameter. In other words, the encoder needs to know how loud the All DRC calculations are relative to and based on the indicated loudness of content as represented Relation to dialnorm content is intended to be so it can determine when the content is either “too loud” or “too quiet.” the loudness of the content. dialnorm effectively sets this target. Therefore, it is very important that dialnorm accurately indicates protection process designed to protect down-mixed audio from overloading consumer equipment. dialnorm is also used to set the threshold of a somewhat hidden and inescapable overload Overload protection has ballistics appropriate for preventing overload but are far less than ideal ensuring that the dialnorm parameter accurately reflects the actual loudness of the audio content. for audio quality. It is good practice to avoid overload protection. This can be accomplished by modes are determined by a group of DRC “profiles.” These profiles describe many parameters, In AC-3 encoders, the gain reduction and expansion characteristics of the RF and Line DRC Professional Encoding release times. In between these ranges is a linear range (or “null zone”) where no gain reduction or including the gain reduction (or “cut”) range, gain expansion (or “boost”) range, and attack and expansion takes place. It is expected that the majority of professionally mixed content will reside within the “null” range, where the content will be delivered exactly as produced, with no specific artistic intent. Note that the dialnorm parameter determines the position of this null band, additional (or continual) modification. Excursions beyond this null band might be to convey a so again, it is essential that the dialnorm parameter accurately indicate the loudness of the content. There are five profiles defined in the AC-3 encoder. The profiles are: • Music Standard • Music Light • Speech • Film Standard • Film Light one or the other may be better applicable to certain types of content. This can be best determined The differences between Music and Film DRC choices may be subtle to a typical listener but by monitoring with an appropriate emulator. The “Light” versions of the profiles have a much wider null area. Thus, gain reduction or expansion begins farther away from average program Profile. The Speech profile is, as the name would suggest, intended for programs that contain only audio, resulting in less gain reduction or expansion than with the “Standard” version of the profiles. on programs with music and effects. Please refer to Annex F for more information about the DRC speech (a “talk radio” format, for example). This profile might introduce noticeable DRC artifacts There is also a choice called “None” that does not select one of the named DRC profiles. The AC-3 DRC: Choosing “None” selection of “None” (by the operator) inhibits the generation of DRC control words. • The reversibility feature of the DRC system will not be available to the consumer. understood: “None” is an acceptable choice as long as the ramifications of not choosing a DRC profile are • Selecting “None” prevents the viewer from selecting a DRC choice or enabling features • Dynamic range should be controlled in another fashion by the operator or by the program mode. such as “Late Night” or “Midnight,” in some consumer equipment that use the RF DRC originator. reproduction range. • There is a possibility that DTV sets with limited volume capacity will exceed their setting combined with very dynamic programming. Choosing “None” will not prevent the prevents clipping in consumer decoders, which could result from an inappropriate dialnorm • The RF mode DRC control words are also used for protection limiting. Protection limiting very artistic. The protection limiting process has a very short attack time and a very long generation of protection limiting DRC control words, which are very aggressive and not release time, and might cause objectionable audible artifacts. • Systems using ATSC signals as a source for SD distribution (e.g., SD analog cable tiers) reduced dynamic range. See ATSC Recommended Practice A/79 [24] for additional will not be able to use the RF mode DRC to establish an acceptable analog SD signal with In order for the AC-3 dynamic range control system to be functional, a profile other than “None” guidance. should be used by operators when appropriate. Loudness Measurement & Monitoring

Dynamic Range Control Monitoring
Dynamic range values shown in Dolby Status display. Monitoring function allows dynamic range parameters to be applied Selection for:- Line Mode RF Mode Within the waveform monitor the dynamic range parameter can be displayed within the Dolby Status display that decodes the metadata. Additionally for monitoring of the audio these dynamic range parameters can be applied for the line and RF modes to the audio outputs from the waveform monitor. This configuration is selectable within the Dolby D setup parameters within the config menu. Monitoring There are benefits to using a system where the DRC “gain words” (see Annex F) are calculated in the encoder and applied at the decoder. One benefit of this type of system design is that it allows the compressor/limiter functions to be accurately previewed, or emulated, during production, well before the content ever gets encoded. Producers can check content as it is being produced to hear how they will sound using pre-established dynamic range modes. While the effects of this DRC system will be audible to mixers in a professional monitoring environment, the process should be considered in the context of the typical consumer in a typical home environment, where such gain reduction and expansion are usually not noticeable. In most situations, the effects of Line Mode DRC generally improve the portrayal of the content by better fitting the audio within the reproduction capabilities of the viewer’s equipment and listening space. Loudness Measurement & Monitoring

Conclusion Audio Loudness is becoming a critical measurement
ITU-R BS 1770/1 and ATSC A/85 have been adopted by broadcasters We expect EBU R128 will be adopted by EBU member broadcasters New Audio measurement tools are needed New work practices need to be adhere by program producers and broadcasters Audio Loudness is becoming and is a critical measurement to make within the broadcast chain to ensure consistent audio levels between programs. The ITU1770/1771 and ATSC A/85 recommended practice have been adopted by broadcasters in order to standardize the measurement of audio loudness. New audio measurement tools are required to measure the loudness of the audio signal in accordance with this standard and new working practices are required in order that program producers and broadcasters can adhere to these practices and produce an consistent overall loudness between programs and intersitital material. VID-11 Loudness Measurement & Monitoring

TEKTRONIX PRODUCTS AND DOLBY
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Dolby LM100 and Tektronix Products
Title Duration Mathematical LKFS UnGated LM100 WFM7120 Cerify Comedy 03:56 -14 The Potters Field 03:08 -18.1 -18 Somebody To Love 04:57 -13.9 Another One Bites the Dust 03:37 -15.9 -16 Cerify will store the loudness peak

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