>> A normal CD is 40 kHz, so 4000 kHz would be 10x *higher* resolution than
>> normal. And 4 bits per sample would be almost unrecognisable.
>
> CD is 44.1kHz, dual channel, 16 bits per sample (linear PCM).
>
> I guess Alain was thinking of a recording at 4000 Hz.

Which would put the Nyquist limit at a piffling 2000 Hz. Even POTS 
manages better bandwidth than that. Note that 2000 Hz is roughly 2 
octaves above middle C. And that's only the fundamental frequency, 
ignoring all the harmonics. Note also that the human voice runs well 
outside that range as well.

> 4 bits sampling does in fact exist

Indeed. It depends on what you're trying to sample. Some applications 
might not need high spatial resolution. Others might not need high 
temporal resolution. For example, we sample the output of our mass 
spectrometers at about 4 Hz. The signal changes so slowly that there's 
really no need to sample any faster.

I would suggest, however, that 4 bits/sample would be inadequate for 
audio applications.

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