Digital Audio SystemPCM streams have two basic properties that determine their fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that each sample can take.

Sampling and quantization of a signal (red) for 4-bit PCM

Digital Audio SystemFor example, a CD audio has a sampling rate of 44.1KHz (44,100 samples per second) and 16-bit resolution for each channel.

PCM is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems.

PCM was invented by Alec Reeves in 1937

Digital Audio SystemConversion Process♦ The digital signal may then be altered in a process which is called DSP where it may be filtered or have effects applied

♦ The last step is for digital audio to be converted back to an analog signal with a DACo Like ADCs, DACs run at a specific sampling rate and bit resolution but through the processes of oversampling, upsampling, and downsampling, this sampling rate may not be the same as the initial sampling rate.

Digital Audio SystemConversion Process♦ The digital audio signal may be stored or transmitted

o Digital audio storage can be on a CD, a digital audio player, a hard drive, USB flash, CompactFlash, or any other digital data storage device

Digital Audio SystemConversion Process

o Audio data compression techniques such as MP3, AAC(Advanced Audio Coding), Ogg Vorbis or FLAC(Free Lossless Audio Codec) are commonly employed to reduce the file size. Digital audio can be streamed to other devices.

Analog Audio SystemDigital Audio System