[vorbis-dev] Monty on holiday

[Willmore, David VS Central]

There had been some talk on this group about another vocoder for low bit
rate use in Vorbis.  

Yes, you're right that most amateur packet radio is 1200 baud (minus
headers, protocol, etc.) and isn't much useful for speech.  I'm looking into
other uses within amateur radio--HF for one is going beyond that data rate.

2K4 and 3K2 are becoming possible in a single voice sized channel.  The
benefits of digital coding can make it quite useful even if it doesn't same
spectrum.

Has anyone looked into a way to stream where some data is better coded--more
likely to survive sync loss?  What about channel coding?  It is quite
practical to split a stream into two different priority streams at that
channel level--encode them differently, transmit them, receive them, and
then re-interleave them.  In doing so, one of the channels may have errors
(the primary reason to do this is so that one channel can be better coded
than the other) while the other may not.

This is done in GSM.  There are A bits, B bits, and C bits.  The A bits
*must* survive if the frame is to be recovered.  The B bits are very useful,
but the frame will just be 'noisy'.  The C bits are "yeah, it would be nice
to have them, but it won't kill us."  So, they are encoded differently in
the RF channel (it's more complex than that, but that's the short version).
This allows the A bits to survive when the B and C might not.

Is there some "priority" marker in the streams within Vorbis?  Lower
(transport) layers could benefit from this. :)

Cheers,
David

> -----Original Message-----
> From:	Gregory Maxwell [SMTP:greg at linuxpower.cx]
> Sent:	Monday, June 05, 2000 4:06 PM
> To:	'vorbis-dev at xiph.org'
> Subject:	RE: [vorbis-dev] Monty on holiday
> 
> 
> I'm not so sure that vorbis is ever going to be sutible for most amature
> use. I dunno about world-wide, but in my area (South Florida), packet
> faster then 1200baud is very uncommon.
> 
> I doubt vorbis will be useful under 8kbit/sec. You might want to look at a
> more specialized alg like a modified CELP.
> 
> 

--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/