At 01:52 1998-03-09 +0000, you wrote:
>Hi all,
>
>I'm thinking of building a digital telephone answering system. What I
>really want to know is if there are any good audio compression
>algorithms that I can use.
>
>I'll be using a PIC processor preferably with a multiplication
>instruction. The algorithm can't be too complex because you need to
>compress the data in real time (8 bits, say 10kHz).
>
>Is this possible or are you better off just storing the audio data
>uncompressed? What do you think?
>
>Regards, Danjel McGougan.
>
The very simple method in this case is to use delta-sigma technology.
Instead of storing the full value, store the change. 4 bit change is
probably enough for 8bit value.

Saves half the memory with very little processing.

Actually if the analog in/out is built by a integrator/derivator stage you
only  need a 4-bit A/D and no processing at all!  The PIC, 4 resistors an
OP and a comparator kan form the A/D and D/A stage.

I have seen a integrated solution using a 1 bit delta-sigma and 256Kbit
dynamic RAM.

I believe the Hi8 video recorders use 8-bit logarithmically compressed
data. i.e one bit change nerar zero level is much less than one bit change
near top values.

This technology can be used in conjunction with delta-sigma as well, to
compress the change?

Just some ideas.

/Morgan
/  Morgan Olsson, MORGANS REGLERTEKNIK, SE-277 35 KIVIK, Sweden \
\  mrt@iname.com, ph: +46 (0)414 70741; fax +46 (0)414 70331    /