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Setting Up DSP Processors Gordon Moore CTS 1-800-821-1121.

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Presentation on theme: "Setting Up DSP Processors Gordon Moore CTS 1-800-821-1121."— Presentation transcript:

1 Setting Up DSP Processors Gordon Moore CTS 1-800-821-1121

2 DSP  Digital Signal Processors  Can be any device that modifies a digital signal (video, audio – anything)  In this class – we will be talking about Audio  NOT a “How-to” for specific manufacturers  Use their training

3  Apologies to any Manufacturers whose screens are not featured – no slight intended.  The CONCEPTS are the core of this course - no brands endorsed or rejected.

4 What to expect  Signal pathway organization  Setting the array of “modules” or functions available

5 Why?  Most DSP processors are barely used to their best capability.  Units returned for service usually have just the simplest functions enabled while many enhancements are not touched.

6 Most commonly unused or forgotten  Compressors  Limiters  Input filtering  NOM bus  Delays

7 Most commonly set up functions  Input Gain (But often badly set)  Routing (inputs to outputs)  Equalization for outputs  Controls interfaces

8 DSP organization  Flexible Architecture  Fixed Architecture  Dedicated function (one capability only)  Multi-function with fixed pathway Hybrid Architecture – some fixed, some flexibility in routing

9 Flexible Architecture All functions can be configured in a “drag-n-drop” environment. Audio functions can be placed almost anywhere along the signal chain in any order. Characterized by a drag and drop GUI (Grpahical User Interface) and/or “fuel gauge”.

10 Sample

11 Advantages Complete flexibility – you can do some amazing things within a single box and develop very complex signal paths. Excellent choice for systems where complexity and/or multiple applications may come into play. Airports Large scale paging systems Complex communications systems Very little you cannot accomplish.

12 Disadvantages  Flexible Architecture may be more costly on a per channel basis  Requires more DSP power – memory register stacks must be allocated for any eventuality – code space cannot be optimized.

13 Fixed Architecture  Dedicated function  Does one type of function  Compression/limiting  Or  Equalization  Or  Signal Routing

14 Advantage Fixed architecture is simple to set up and operate – may not even require a computer Less cost for the box – may not be as cost effective as a combined DSP capability Sets up much like analog counterpart Excellent choice for existing system upgrade

15 Disadvantage  Very limited in scope of function  May not be very scalable

16 Fixed Architecture Multi-function Has multiple functions in a fixed pathway Generally fairly cost effective Limited in terms of routing and or set up choices. Advantage – predictable known good pathway No gauge Disadvantage – few if any routing choices

17 Hybrid Architecture  Combination of routing choices plus fixed multiple function signal pathway  Advantages –  Allows flexibility as far a signal routing goes – what inputs show up at what outputs  Optimizes DSP processing power – memory stacks and registers can be more tightly packed  Disadvantages  May not fulfill all needs in a system

18 Hybrid Architecture


20 Enough Boring stuff – Let’s set up some functions  Input Gain  Filters – Input and/or Output  Equalization  Feedback suppression  Crossovers  Noise reduction  Dynamics  Compressors  Limiters  Gates  Routing

21 Dynamics  Those functions affecting gain structure and levels

22 INPUT GAIN  Most important setting – GET THIS RIGHT!  Always set up – but not necessarily well set up  Microphones  Handheld Vocals = 35dB minimum  Handheld Presentation = 45dB  Gooseneck desk = 45dB  Boundary mic = 55dB  Any further away = 60db+  Ceiling – as hot as you can get it

23 INPUT GAIN  Multimedia  Unbalanced? Consumer = +10  Balanced? Professional = 0 to -8

24 Signal to noise ratio MicPreampMixerSignal processorsAmps Line Level Mic Level Noise Floor Poor S/N Ratio

25 Signal to noise ratio MicPreampMixerSignal processorsAmps Line Level Mic Level Noise Floor Good S/N Ratio

26 Signal to noise ratio MicPreampMixerSignal processorsAmps Line Level Mic Level Noise Floor

27 THRESHOLDS  The level at which the desired function becomes active  Generally speaking a lower threshold level means it will activate earlier.  Recommended starting threshold for most line level (post preamp) functions = 0dBu

28 AGC and/or Levellers  Automatic Gain Control  RAISES gain if signal too low  Compresses if signal too high  BE VERY CAREFUL with these  Can run a room into feedback if used on amplified inputs  Primary application – to capture weak signals for recording or transmission  Start with threshold set at 0dB – keep gain centered at line level

29 Ambient Level Control Uses a reference microphone to measure room noise level the automatically adjusts system for noisier environment Reference microphone may be dedicated microphone – only purpose is reference, or may be designated microphone – used in system but designated to be the reference signal Read the manual


31 COMPRESSORS  Control dynamics - loudest to softest  Useful for keeping level under control  Meek versus motivational speaker  Rarely set up

32 Compressor settings - Ratio  Ratio – The amount of actual level increase above threshold that will yield ONE decibel in actual gain change after the compressor.  Example – 3:1 ratio  For every 3DB the gain increases above threshold, the final level will change only one dB  SO, if level jumps 9DB, the final level will jump only 3dB  FM is broadcast at typical 10:1 ratio

33 Compressor settings – Threshold, Attack, Release  Threshold - Level at which compressor begins to engage and affect level.  Attack – time in milliseconds the compressor begins to make changes after level exceeds threshold  Release – time in milliseconds the compressor lets go after level settles below threshold.  Makeup or post compressor gain  Compensation in level to make up for compressor reduction in signal.

34 Suggested setting for compressors  Speech systems (conference rooms, boardrooms, etc) Ratio = 3:1 Attack = 10-20ms Release = 200-500ms Threshold = 0 If initial input gain was set to result in 0dB level, then it would take a 60dB increase at the mic to hit the +20dB limit of input (clipping) MUSIC or Multimedia – try increasing ratio to 6:1 BE CAREFUL – too much = bad

35 LIMITERS  Basically, a compressor with an infinite ratio  Absolute ceiling to maximum level  Protects downstream gear by preventing severe clipping and overdriving amps and speakers  Many amplifiers have built in limiters to protect themselves.  ALWAYS set limiter threshold above threshold of compressor  Otherwise, compressor will never engage  Good for spikes like dropped microphones, cymbals, plosives (P,D,T)

36 Suggested Limiter settings  Threshold – 15db higher than compressor = +15dB if 0dB for compressor  Attack – faster than compressor = 2ms or quicker  Release – 200ms or less

37 Some dynamics filters can be frequency specific  Compressor with low pass filter good for controlling proximity effect while allowing high frequencies to pass unaffected.

38 EXPANDERS  Increases gain if signal very low such as weak talker  BE VERY CAREFUL HERE – Expanders, in an amplified environment, can push system into ear bleeding feedback.  Primarily intended for recording and or transmission.

39 GATES  Gates activate a channel, allowing it to pass, once the level passes above the threshold.  Found in some automixers  Useful for noise control (noisy multimedia source, for example)  Originated in music

40 Attack, Release, Threshold  Attack – try relatively fast settings, 1ms to begin  Release – start at 50ms  Threshold – depends on place in chain  If after input gain – 0dB is a good starting place  Lower if not getting a reliable start

41 Noise Gate

42 Spectral  Affects the frequency response of the system

43 EQUALIZATION (Inputs)  Equalization is one of the most commonly used functions  Input EQ is generally for tonality control – adjusting the tonal content so each input sounds similar.

44 EQUALIZATION (Outputs)  Generally used for speaker compensation  Adjusting for “quirks” or characteristics in the loudspeaker response.  You cannot EQ a “room”

45 Equalization patterns  Pass – Low, High or Band  Shelving – Low or High  Parametric - Notch  Graphic

46 “Q”  No, not James Bond’s gadget guy  The ratio of filter width to depth at 3dB roll off points

47 Low Q – Wide band width

48 High Q – Narrow Band width

49 Filter Slope or “Order”  Rate of attenuation on filter - Shown in terms of dB/octave  Octave – doubling of frequency  First order = 6dB per octave  Second Order = 12dB per Octave  Third Order = 18dB/Octave  Fourth Order – 24dB/Octave  Each order equals another 6db of roll off.  That means 4 times factor in power level  If 6 db down from 100watts = 25 watts.

50 First Order – 6dB per octave (High pass)

51 Same filter – Second order

52 Eighth Order- 48 dB/octave

53 Parametric  Fully configurable  Boost or Cut adjustable  Center Frequency selectable  Q selectable

54 Parametric

55 Band Pass

56 Low Pass

57 High Pass

58 Shelving – Boost or cut, High or Low

59 Filters - Graphic EQ

60 CROSSOVERS  Used for bi-amplified and tri-amplified systems  Low frequency content sent to bass amplifiers  Mid and high range sent to appropriate amplifiers  Separate amplifiers involved  Large scale concert systems  High order - 4 th to 8 th order filters  Bass – 250Hz or lower  For tri-amplified – start at 4K for high pass


62 FEEDBACK SUPPRESSION  Should be set up LAST after Equalization  Smooth response FIRST, then take care of Feedback nodes  A time domain issue coupled with Frequency domain  Notch Filters – very tight  But too many can badly affect content

63 Set up tip – One mic at a time  1. Before final EQ – run feedback “eliminator” first  2. Make note of first three feedback freqs  3. Construct three very tight notch filters at INPUT on those frequencies  4. Reset the feedback filters  5. engage feedback filters again after equalization and system is at operational levels.

64 NOISE REDUCTION  Popular new algorithms that “sample” the noise floor  Noise floor – acoustical and electronic noise that is NOT wanted in system  Air Conditioning  Fan noise  Laptops near boundary mics  computers  Projectors  Electronic noise – noisy sound cards in computers etc.

65 Setting Noise Reduction Filters  Canceller Depth – depends on the amount of noise  Quiet conference room with little to no noise may not need this.  Computer and projector fan noise – try starting at 9dB.  Heavy room noise – large attendance training room or bad air conditioning rumble, try 12dB  Remember, these filters remove spectral content – none are perfect and they will all affect your room response.  DON”T GET CARRIED AWAY!


67 Signal Generators  White noise – equal energy per frequency  Pink Noise – equal energy per octave  Tones  Primary use – test and measurement  Use pink noise to set up your levels in the room  If your gain structure is correct – this will allow amplifiers settings tobe accurately set up  Use test tones for gain staging and/or speaker alignment  Secondary Use  Noise masking – covering conversation or background ambient noise  Alarms

68 ROUTING  Matrix –  Rarely overlooked  Determines which inputs go to which outputs  (technically speaking “gozindas to gozoudas”)  Some traps here  Watch for  Feedback loops  NOM bus assignment – VERY IMPORTANT

69 Selecting NOM bus and action  NOM= Number of Open Microphones  Determines interactions of microphones in automixing  Failing to select correct NOM interaction can affect echo cancellation, and gain before feedback  Choices may include  Chairman Over-ride  Auto mix (or Normal)  Background (or Ducking)

70 Feedback loops  Common error in setup – requires careful documentation and double checking – especially when dealing with mix minus conferencing systems. Sending an input BACK to itself.

71 Delays  Often neglected  Primarily used for time alignment  Loudspeaker stacks in large venues  Input alignment  Loudspeaker alignment  Secondary use for spatial referencing (Haas effect)  Localization of sound based on first heard  Set up tip –  Try setting for 10ms or 10ft or 3.3m FARTHER than distance would indicate.  Example – Speaker is 68 ft from stage – instead of 60.5ms, try 70.5.

72 Some architectural Do’s and Don’ts  In Flexible Architecture – General rules – always exceptions  Do NOT put compressors before Equalizers/Filters  The EQ can take out energy that would falsely trigger compressor – so put compressor AFTER filtering  Do NOT put limiters before compressors -  Do NOT put limiter thresholds lower than other devices – especially compressors  Be careful about thresholds for automixers – (gated designs)  Too low and room noise will open mics  Too high and you may lose the first characters  Shared gain mixers will not have thresholds

73 Hybrid Architecture Do’s and Don’t  Don’t create a feedback loop – be careful where you send inputs  Don’t go overboard on settings  “Too much of a good thing is wonderful” does NOT apply here.

74 Troubleshooting tips  Ringing or severe echo in audio  Internal feedback loop  Signal generators or incoming conferencing too loud  Poor input gain structure – HOT IT UP!  HISSssssssssss or noisssssssse in system  Bad gain structure – inputs too low – Amplifiers too high  University reasoning – wrong solution to the right problem.  Amps set to full output  Inputs set low  Correct solution – lock up the amplifier controls.

75 Questions?  Fill in your reviews please!

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