Bit depth

In digital audio, bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data. Common examples of bit depth include CD audio, which is recorded at 16 bits, and DVD-Audio, which can support up to 24-bit audio.

Bit rate refers to the amount of data, specifically bits, transmitted or received per second.

One of the most common bit rates given is that for compressed audio files. For example, an MP3 file might be described as having a bit rate of 160 kbit/s or 160000 bits/second. This indicates the amount of compressed data needed to store one second of music.

The standard audio CD is said to have a data rate of 44.1 kHz/16, implying the audio data was sampled 44,100 times per second, with a bit depth of 16. CD tracks are usually stereo, using a left and right track, so the amount of audio data per second is double that of mono, where only a single track is used. The bit rate is then 44100 samples/second * 16 bits/sample * 2 = 1,411,200 bit/s or 1.4 Mbit/s.

This explains why, for example, a Minidisc recorder, which uses ATRAC compression, can store files lasting twice as long on a disc, if the default, recording in 2 channel stereo, is set to single channel mono recording.

To fully define a sound file's digital audio bit rates, the sampling rate, word size, number of channels, (e.g. mono, stereo, four-track), and format of the data also need to be known.

Bit rate
Bit rate refers to the amount of data, specifically bits, transmitted or received per second.

One of the most common bit rates given is that for compressed audio files. For example, an MP3 file might be described as having a bit rate of 160 kbit/s or 160000 bits/second. This indicates the amount of compressed data needed to store one second of music.

The standard audio CD is said to have a data rate of 44.1 kHz/16, implying the audio data was sampled 44,100 times per second, with a bit depth of 16. CD tracks are usually stereo, using a left and right track, so the amount of audio data per second is double that of mono, where only a single track is used. The bit rate is then 44100 samples/second * 16 bits/sample * 2 = 1,411,200 bit/s or 1.4 Mbit/s.

This explains why, for example, a Minidisc recorder, which uses ATRAC compression, can store files lasting twice as long on a disc, if the default, recording in 2 channel stereo, is set to single channel mono recording.

To fully define a sound file's digital audio bit rates, the sampling rate, word size, number of channels, (e.g. mono, stereo, four-track), and format of the data also need to be known.

Calculating values
There is an easy way to determine a file's bit rate when given sufficient information. In fact, as long as you know any three of the following four values, you can calculate the missing value.

Bit rate = (bit depth) x (sampling rate) x (number of channels)

For a recording with a 44.1 kHz sampling rate, 2 channels (stereo) and a 16 bit depth: 16 x 44100 x 2 = 1411200 bits per second, or, 1411.2 kbit/s

Also see

 * Audio_sample_rate_and_bit_depth_tutorial