Digital Recording

Digital recording is different from analog in that it doesn’t operate in a continuous way; it breaks a continuously varying waveform into a sequence of individual amplitude assessments called samples.

Samples are energy readings that occur several times per second. A greater number of readings will yield a recording that is closer to reality.

Advantages to digital recording over analog:  excellent signal to noise ratio (no tape hiss)  copies can be as good as the original  data can easily transferred between various types of media  data storage is relatively inexpensive  data storage is accurate and relatively reliable

Advantages: continued  data is easily manipulated (cut, copy, paste…etc.)  locating musical sections is instantaneous (No rewind time)  sound quality of the recording does not degrade with each recording take.  The technology is relatively affordable.

Digital Audio Theory In the world of digital recording the information is encoded as a series of “0”s and “1”s. Data is represented by a series of binary data that is referred to as Pulse Code Modulation (PCM).

The quality of a digital recording is determined by two main factors:  Sample rate (horizontal resolution)  Bit resolution (vertical resolution)

4 Bit Sample

A) Sample rate (horizontal resolution)  The process of sampling (digital encoding and decoding) breaks the time axis (horizontal) and voltage axis (vertical) into a specific number of steps. At each step along the time axis a measurement is taken of voltage (amplitude) status. The sample rate is the number of times per second that the processor samples the voltage (amplitude) of an analog waveform.

The Nyquist Theorem states that in order to accurately sample a sound, the sample rate has to be at least twice the desired highest frequency. Therefore, to accurately and faithfully reproduce a frequency of Hz (the upper range of human hearing) the sample rate must be at least (2 x Hz) or Hz.

This is why the standard audio CD sample rate was fixed at Hz (44.1 kHz). Most people feel that 44.1 kHz is an ample sample rate to capture the frequencies inherent in recorded sound. However, recording engineers and physicists know that sound perception involves more than just distinguishing frequencies

Stereo localization of sound  Frequency perception of a sound is complicated somewhat by the fact that we have two ears. Our brains perceive sounds on a three-dimensional plane. This concept is sometimes referred to as triangulation.  The brain localizes sound by calculating the time delay difference between the arrival of a sound at each ear (Haas effect). 15 microsecond time differences are discernible by almost everybody. Some people can even perceive time differences as little as 5 microseconds between ears.

Because we perceive these small time differences between ears, the current standard sampling rate of 44.1 kHz is really not enough to deliver the level of stereo localization that our ears demand.

 At a sampling rate of 44.1 kHz the samples are 23 microseconds apart.  At a sampling rate of 48 kHz the samples are 20 microseconds apart.  At a sampling rate of 96 kHz the samples are microseconds apart.  At a sampling rate of 192 kHz the samples are microseconds apart.

THE FUTURE?  It is believed that someday 192 kHz will likely be the standard sampling rate for all professional sound recording.

B) Bit Resolution (vertical resolution)  At each sample point, signal strength (amplitude) is calculated. The sample strength is measured against a discrete number of vertical increments. To achieve greater precision in resolution requires that we aim for a greater number of vertical increments.

CD’s are recorded at a 16 bit resolution. This means that each bit has a word length of at least 16 digits (example: ). A greater the number of digits in a bit- word provides a more precise vertical measurement of signal strength.

There is a simple formula to calculate the number of vertical increments if we know the length of the bit word. If “n”= the length of the bit word (bit resolution). 2ⁿ = number of vertical increments

Let’s use the formula to calculate the number of vertical increments for a standard 16 bit resolution CD audio recording = 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 = vertical increments

Because bit resolution uses an exponential formula even a small increase in bit rate offers a significant increase in resolution.

The table below should give you a pretty good idea: Bit resolutionVertical increments

Computer soundcards and audio interfaces with the capability for 24 bit resolution and 192 kHz sampling rates are currently available. This will likely become the standard for all professional audio recording in the next few years.

Keep in mind that when we increase the sample rate and bit resolution we are also increasing the amount of data that the computer has to manage. When assembling a computer for professional audio work it is important to aim for a fast processor, a large/fast hard drive and, most importantly, lots of RAM.

Digital Audio Formats Compressed: MP3, MP4, WMA, ATRAC, RA, RAM, OGG,FLAC, AAC ….and the list goes on ! Uncompressed: WAV (Windows), AIFF (Apple), AU (Sun)

Consumer digital playback devices:  CD players  DAT  Computers  Mini Disc  iPods and Mp3/WMA file players  Super-Audio CD players (SACD)  DVD-Audio  BLU-Ray or HD-DVD …future?

Final Thoughts ! Artists are currently recording and mixing their music at increasingly higher sample resolution and bit rates. They can even make a mix in 7.1 channel surround sound. The problem is that most listeners are not really concerned with the actual sound quality of their music. The problem is that most listeners are not really concerned with the actual sound quality of their music.

If sound quality not really a priority, what is?  cost?...free  speed and efficiency of delivery  storage space  portability  wide selection of choices