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> If anyone knows of _ANY_ software implementation of CVSD
> (for any machine) for which source is available I would be
> EXTREMELY appreciative.
>
> Bob Ammerman
> RAm Systems

This is the block diagram of a DSP I hope to emulate in s/w

In record mode, the input comparator is compared to the output
of the 10-bit DAC at the sample moment, and the output of the
comparator (0 or 1) is stored in RAM. The output of the DAC
can be monitored audibly, so that the sampling speed can be
optimised for length of sample vs fidelity. 12 seconds of audio
at tape quality (16kHz) can be stored in 1Mbit RAM. I've found
that with a slow chip clock and external filtering to remove
sampling alias it's possible to record 2 minutes of speech at
acceptable fidelity in 1Mbits

In playback mode, the 8-bit data stored in RAM is left-shifted
twice into a 10-bit register (the 2 LSBs are padded with 0s)
and fed into the Estimate Integrator & Syllabic Integrator. Here
it gets a little hazy, as overall the poor Japanese-English translation
is not very detailed. I quote - "The output of the D/A convertor is
produced by the estimate integrator and sillabic integrator based
on the previous sampling data value". The serial data stream is a
sequence of differences. For example, shorting the input (or holding
it at any DC level) produces stored values of $55 and $AA (or binary
01010101 and 10101010). What I have not been able to find are
satisfactory explanations of "Estimate Integrator" and "Syllabic
Integrator". Because the DSP is h/w only I assume that there is
some process inside that uses an RC set-up. If anyone has an
idea of whether this is a mathematical or engineering function I'd
love to know about it

I'm confident that the impressive functions of a 15 year old DSP
running at typically 600kHz-700kHz can be implemented on a
mid-range PIC at 20MHz. The 10-bit DAC may need to be external

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