Digital Recording

In analog recording, the waveform of a signal being processed resembles the waveform of the actual sound itself. The analog signal is a continuous waveform, made up of an infinite number of points. In order to translate the analog signal into discrete digital levels, there are a 2 main parameters to determine- the sampling rate and the bit rate.

Sampling rate is the frequency that a digital sample is taken of the analog waveform. This is measured in Hertz, and is defined as the number of samples per second. An example of a common sampling rate is 44.1 KHz, which means that 44,100 samples are taken per second.

The Nyquist Frequency is defined as the minimum sampling rate that can be used without losing data about the signal. It is 2 times the highest frequency. For example if the highest frequency in a song is 20kHz, you must double this to get the minimum sampling rate of 40kHz. Higher sampling rates (or "oversampling") have a wider/flatter frequency response, leading to more clarity and detail in the sound, with low noise and low distortion.

Sampling is the time component, while quantization is the level component (like amplitude for the amplitude signal). Quantization is the process that converts voltages of each sample into a discrete quantity and assigns bit values.

Bits are binary digits, using a base 2 system with either 1 or a 0 value. Decimal is a base 10 system that you are used to - using ten values, 0 -9. In binary, a voltage on represents a 1 while voltage off represents a 0. A digital word is a combination of 1s and 0s that create a distinct value. 10 is a 2 bit word - each n-bit word makes 2^n discrete levels.
1 bit = 2 levels = 1, 0
2 bit = 4 levels = 00, 11, 10, 01
3 bit = 8 levels = 000, 001, 011, 111, 100, 101, 010, 110
etc.

The longer the word length the more quantizing levels that are available and the more dynamic range allowed, or resolution. The higher resolution allows for a more accurate representation of an anolog signal.

Some additional information on binary is available here.

Digital audio is expressed with both items: 16 bit resolution and 44.1 kHz sampling rate.

An example of an early digital system is the DAT recorder, or Digital Audiotape. However, the audio industry is generally going more towards a tapeless system, using flash/hard disk recorders instead.

Compression is a method to reduce the size of an audio file, by representing information with the fewest number of bits possible and removing redundancy. MP3s are an example of a codec algorithm that reduces the size from a WAV or AIFF audio file.

Interfacing with digital systems uses different protocols. The most common is the AES/EBU which is a pro audio connection interface standard that is used in XLR cables. Firewire and USB are low cost, flexible, compatible standards used as well.

ISDN (integrated services digital network) is bases on a public telephone all-digital network so that audio professionals can record from across the country without audio quality losses.