Bob Ammerman wrote:
>
> The problems with this RLE encoding thing are:
>
> 1: CVSD type data generally does not have long runs of zeros or ones in it
> because of its very definition: the step size is quickly increased to the
> point where it catches up and goes the other way (ie: the bit polarity
> flips).

Actually I suggested using RLE instead of CVSD,
as a RLE system tuned to a byte-sized data unit
is probably more suited to the minimal PIC approach.

I'm sure you could get 2:1 with the right RLE
system. At the 32kbit/sec rate you suggested
and with 2:1 RLE compression you get good voice
for only 2kbyte per second. That's 3.5 seconds
to 7 seconds of voice on a 16F876. Plenty enough
for many applications of products for the
visually impaired.

> 2: CVSD is a constant-bit-rate scheme. This can be very important when
> transmitting over a serial link (like radio). This RLE scheme is not
> constant bit-rate.

You said CVSD bits change in size. That can't
be a constant bitrate. ??
  >Whats makes it 'Variable' is that the step size is increased whenever
the
  >the transmitter finds itself sending a sequence of more than a couple
of
  >consecutive zeros (or ones),

> 3: CVSD is rather resilient to bit errors in the transmission path. Again
> this would greatly confuse the RLE stuff.


Sure, but if the goal is a simple bitstream
player on a PIC, then RLE decodes very quickly
and minimum PIC instructions. I think it's worth
looking at all simple compression systems
that work that easily.

You could do STEREO 152kbit/sec audio on a
20MHz PIC which gives 32 instructions per 2 bits,
output it on 2 I/O pins into RC filters...
There's time in there for the 32inst timing loop,
loading the data, and RLE compression on 2 bytes
every 8 timing loops.
Isn't that approaching CD audio sound quality?
-Roman

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads