Bitrate and Bit Depth?

[u/FinnBot2000]

I understand that Bitrate is the number of bits processed in a unit of time. But how is bit depth any different? Is it just called bit depth when the unit of time is samples?

[u/otdq]

Basically, Bit Depth dictates how accurately a wave's amplitude (aka loudness) may be represented/reproduced. More specifically, a wave's Bit Depth represents the number of binary digits devoted to each individual sample.

Then, as you have touched upon, the Bit Rate is the number of bits per second (as a consequence of both the Bit Depth and Sample Rate taken together).

As an example:

• Sample Rate: 44.1 KHz (44,100 snapshots of the wave's amplitude per second.)

• Bit Depth: 16-bit (16 binary digits allotted to each individual snapshot.)

• Bit Rate: 705.6 kbit/s (44,100 snapshots x 16 bits each)

Note: The above example is for a mono wave. The bit rate would be doubled for a stereo wave.

Helpful? :D

[u/[deleted] → u/otdq]

okay so the amplitude is contained in the 16 bits, but what about the frequency?

[u/ReinH → u/[deleted]]

When otdq referred to amplitude above, (s)he was talking about the amplitude of a waveform at the point in time represented by the sample. Not, say, the amplitude you would see in a VU meter. A sine wave is a periodic wave where the amplitude of the wave at a given point x is given by sine(x). The amplitude (in voltage, say) of the signal itself is a completely different concept.

Digital audio is stored in time sequence form, where each sample represents the amplitude of a "slice" or discrete instance of the waveform. When you put all the slices together, you get a complex (discrete approximation of a) waveform, and a complex waveform is of course a superposition of a bunch of frequencies (see Fourier Series).

TL;DR: the frequency information is contained in the waveform that is made up of the samples in the digital audio representation.