Audio Bit Depth - Applications

Applications

Telephone applications frequently use 8-bit quantization. That is, values of the analogue waveform are rounded to the closest of 256 distinct voltage values represented by an 8-bit binary number. This crude quantization introduces substantial quantization noise into the signal, but the result is still more than adequate to represent human speech.

Standard DV audio is 12-bit (4096 levels), NICAM pseudo-14-bit (10-bit data + 4-bit gain signal, with 14-bit output DAC).

Compact discs use a 16-bit digital representation, allowing 65,536 distinct levels. This is far better than telephone quantization, but CD audio representing low signal levels would still sound noticeably 'granular' because of the quantizing noise. However, sometimes an addition of a small amount of noise is added to the signal before digitization. This deliberately added noise is known as dither. Adding dither eliminates this granularity, and gives very low distortion, but at the expense of a small increase in noise level. Measured using ITU-R 468 noise weighting, this is about 66dB below alignment level, or 84dB below FS (full scale) digital, which is somewhat lower than the microphone noise level on most recordings, and hence of no consequence (see Programme levels for more on this).

Enhanced CDs, SACDs and DVD-Audio can use 20 or even up to 24-bit sampling (>16 million levels). CD Audio has also left a lasting impression on computer and other digital audio applications, where 16-bit is the default "hi-fi" sample resolution (as opposed to earlier 8, 6 or even 4-bit efforts), with higher precision often considered the reserve of audiophiles as the representable range of intensities rapidly exceeds the theoretical limits of human perception, particularly when environmental noise is considered.