Sample Rate and Bit Depth

Digital audio stores sound as a long list of numbers. An audio interface measures the height of the sound wave at regular moments, called samples, and records each one as a number. Two settings describe how it does that.

Sample rate: how often

The sample rate is the number of measurements per second, given in hertz or kilohertz (kHz).

• 44.1 kHz (44,100 samples per second) is the standard for audio CDs.
• 48 kHz is the usual standard for video and film sound, and many studios record music at it too.
• 88.2 kHz, 96 kHz and higher rates are also used in recording.

Digital audio can represent frequencies up to half its sample rate, a limit known as the Nyquist frequency. At 44.1 kHz that is 22.05 kHz, comfortably above the roughly 20 kHz upper limit of human hearing. Higher rates matter mainly for some kinds of processing and for extreme pitch or time changes; whether they make an audible difference to the final listener is debated.

Bit depth: how precisely

Bit depth is the number of bits used to store each sample. It sets how finely the level can be measured, and so how far the quietest detail sits above the background noise of the system.

• 16-bit is the CD standard, with a theoretical dynamic range of about 96 decibels.
• 24-bit is the common choice for recording, about 144 dB in theory, which leaves plenty of room to record at safe levels without audible noise.
• 32-bit float is used inside most DAWs (some process at 64-bit float), and by some recorders, because it can hold extremely loud and extremely quiet values without clipping inside the software.

When audio is reduced to a lower bit depth, for example from 24-bit to 16-bit for a CD, a tiny amount of noise called dither is usually added to make the conversion cleaner.

Practical settings

• A sensible default for recording music is 48 kHz or 44.1 kHz at 24-bit.
• Choose the rate at the start of a project and keep it: every file in a session should share it.
• Higher settings make bigger files. One minute of stereo audio at 48 kHz/24-bit takes about 17 MB, against about 10.6 MB at 44.1 kHz/16-bit.
• The final format depends on where the music is going: 44.1 kHz/16-bit for CD, 48 kHz for video, and each streaming or distribution service publishes its own requirements (mastering).

The word sampling has a second musical meaning, reusing recorded sounds in new music; see sampling.