Difference between sampling rate, bit rate and bit

问题:

This is kind of a basic question which might sound too obvious to many of you , but I am getting confused so bad.

Here is what a Quora user says. Now It is clear to me what a Sampling rate is - The number of samples you take of a sound signal (in one second) is it's sampling rate.

Now my doubt here is - This rate should have nothing to do with the quantisation, right?

About bit-depth, Is the quantisation dependant on bit-depth? As in 32-bit (2^32 levels) and 64-bit (2^64 levels). Or is it something else?

and the bit-rate, is number of bits transferred in one second? If I an audio file says 320 kbps what does that really mean?

I assume the readers have got some sense on how I am panicking on where does the bit rate, and bit depth have significance?

EDIT: Also find this question if you have worked with linux OS and gstreamer framework.

回答1:

Now my doubt here is - This rate should have nothing to do with the quantisation, right?

Wrong. Sampling is a process that results in quantisation. Sampling, as the name implies, means taking samples (amplitudes) of a (usually) continuous signal (e.g audio) at regular time intervals and converting them to a different represantation thereof. In digital signal processing, this represantation is discrete (not continuous). An example of this process is a wave file (e.g recording your own voice and saving it as a wav).

About bit-depth, Is the quantisation dependant on bit-depth? As in 32-bit (2^32 levels) and 64-bit (2^64 levels). Or is it something else?

Yes. The CD format, for example, has a bit depth of 16 (16 bits per sample). Bit depth is a part of the format of a sound (wave) file (along with the number of channels and sampling rate). Since sound (think of a pure sine tone) has both positive and negative parts, I'd argue that you can represent (2^16 / 2) amplitude levels using 16 bits.

and the bit-rate, is number of bits transferred in one second? If I an audio file says 320 kbps what does that really mean?

Yes. Bit rates are usually meaningful in the context of network transfers. 320 kbps == 320 000 bits per second. (for kilobit you multiply by 1000, rather than 1024)

回答2:

Let's take a worked example 'Red-book' CD audio

• The Bit depth is 16-bit. This is the number of bits used to represent each sample. This is intimately coupled with quantisation.
• The Smaple-rate is 44.1kHz
• The Frame-rate is 44.1kHz (two audio channels make up a stereo pair)
• The Bit-rate is therefore 16 * 44100 * 2 = 1411200 bits/sec

There are a few twists with compressed audio streams such such as MP3 or AAC. In these, there is a non-linear relationship between bit-rate, sample-rate and bit-depth. The bit-rate is generally the maximum rate per-second and the efficiency of the codec is content dependant.