🚀 go-pugleaf

>>  What is 'bitstream conversion' for a CD player?
>Anyone?

If I'm not mistaken, bitstream is the marketing term for
Delta-Sigma Modulation (sometimes called Sigma-Delta
Modulation; but that's another story :-). 

As Bill Eason (gt8021a@prism.gatech.EDU) points out, increasing
the sampling rate relative to the bandwidth of interest reduces
the burden on the antialiasing and anti-imaging filters. In
addition, however, for the same SNR (in the bandwidth of
interest) you can use a DAC (or ADC) of lower precision (fewer
bits) as long as you arrange for the increased quantization
noise to lie outside this band. Lower precision DACs and
ADCs are, obviously, easier and cheaper to manufacture and DSM
allows for a tradeoff between speed for precision.

Pushing this to its logical extreme, with sufficiently high
sampling rates (say 128*Nyquist) and noise-shaping one can use
one-bit DACs and ADCs. The output of a one-bit DSM would be a
one-bit stream that you could low-pass filter with a resistor
and capacitor.

There are a number of commercial A/D and D/A parts that make use
of DSM; possibly the most famous of these is Motorola's 16-bit
A/D DSP56ADC16. Most A/D's decimate the bit stream to produce
16-bit wide words at little over the Nyquist rate for
processing via standard DSP uPs.  It is, however, possible (and
often advantageous) to process the DSM signal directly without
the added burden of decimation and interpolation.

   0>------[DSM]-----[PROCESSING]------[RC network]----->
  sensor     A/D                       (simple D/A)      output

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Anees Munshi, University of Toronto, Department of Electrical Engineering
Email:asm@eecg.toronto.edu (NeXT mail accepted)
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