Quantizing bit rate below 8-bit

[Vitnim]

Audacity 2.0.3
OSX 10.9.1 (Not by choice!)

Hello all,

I am teaching a high school Music unit on technology, and we are studying waveforms and the analogue<->digital conversion. What I would like to do is have the students take a sample of sound/music and resample it at various rates and analyze the effects. With Audacity, it is easy enough to change the sample rate in Hz, but it seems to me that I am stuck with choosing between 16, 24, and 32 bit rates. 8-bit also seems doable by exporting to 8-bit PCM WAV. I would like to go even further, however. So my questions:

1. Is it possible to quantize lower than 8, or to any rates other than 8, 16, 24, or 32 in Audacity?
2. Even if I succeeded, is there any reason Audacity or any other music player wouldn't be able to support other bit rates?
3. If it is not possible in Audacity, does anyone know what else I might try? ffmpeg or something?
4. Am I using the term quantize correctly??

Thanks!

[steve]

You are mixing up the terms "bit rate", "bit depth" and "sample rate".

"Bit Depth" (also called "bit format") is the numerical format used to represent each sample.
Typically this will be 8, 16, 24 or 32 bit, though others are possible, and there are also variations including "signed integer", "unsigned integer" and "floating point".

A higher bit depth provides greater accuracy in representing the amplitude of the waveform, hence it provides greater dynamic range (the range between the maximum signal and the digital noise floor).

Bit depths lower than 8 bit are rarely used in audio except in some old compressed formats such as ADPCM (http://en.wikipedia.org/wiki/Adaptive_d ... modulation).

"Bit Rate" refers to the number of "bits" (binary digits) per second.
"Sample Rate" refers to the number of samples per second.

Digital audio can represent frequencies up to a maximum of half the sample rate (the "Nyquist Frequency" http://en.wikipedia.org/wiki/Nyquist_frequency).


If you have 8 bit samples and 1000 samples per second:
The "bit depth" is 8 bit.
The "sample rate" is 1000 Hz ( 1 kHz )
The "bit rate" is 8000 bits per second ( 8 kbps )

[Trebor]

1. Is it possible to quantize lower than 8, or to any rates other than 8, 16, 24, or 32 in Audacity?

see Nyquist Prompt ... http://manual.audacityteam.org/o/man/ny ... rompt.html

NB: the bit-depth is half the quantize value , e.g. in this case 5 , ("10"/2).

quantize.png (5.17 KiB) Viewed 2882 times

2. Even if I succeeded, is there any reason Audacity or any other music player wouldn't be able to support other bit rates?

Using quantize in Nyquist Prompt the output can still technically be say 16bit WAV , so playable on any mediaplayer ...

Dubya, then progressively decreasing 'quantize' value.wav

(884.02 KiB) Downloaded 132 times

You're not going to achieve any file-size reduction using 'quantize' in Nyquist-Prompt alone.

... does anyone know what else I might try? ffmpeg or something?

If you don't like using the Nyquist-Prompt , see the free "degrade" VST to lower bit-depth here ... http://mda.smartelectronix.com/

[Vitnim]

steve - Thank you for pointing out my error in expressing depth as rate. I will make sure I don't make the same mistake when explaining to my students.

Trebor - That is EXACTLY what I wanted. I'm not surprised that Audacity had the feature inside its guts somewhere, but I am happy to find out how to access it!

Thanks for your help!