[hfsig] Is there anyone out there?

Charles Brain chbrain at btinternet.com
Mon Oct 12 15:57:40 EDT 2009

Hello Moe,

Well good luck to them, I have been experimenting with low rate vocoders
and I have got to the stage where to reduce the bitrate any further I need to 
use a split VQ codebook. Building such a codebook means either stealing 
the one out of the MELP standard (not a good idea) or getting loads of 
sound samples of many speakers then running them through my code to generate 
the LSFs then finding the centroids of the groups of LSFs then building a 
split codebook from that (a non trivial task). 

I have code that does the LPC analysis, generates the LSP/LSFs, tracks the pitch
and makes the voiced unvoiced decisions. I recently started playing with post 
synthesis spectral enhancement filters. 

I have been tinkering with this on and off for about 5 years and while it is getting better 
it is still 'no cigar yet'! 

- Charles

----- Original Message ----- 
From: "bellsouth" <ae4jy at bellsouth.net>
To: "TAPR HF Modes SIG Mailing List" <hfsig at tapr.org>
Sent: Monday, October 12, 2009 8:34 PM
Subject: Re: [hfsig] Is there anyone out there?

> Hi Charles,
> You need to post something outrageous like you've found a way around Shannon 
> Capacity Limit or Nyquist rate then they will come out of the woodwork. :)
> The most interesting new thing I've run across lately is this project:
> http://www.rowetel.com/ucasterisk/codec2.html
> May be a path to get away from the AMBE vocoder and have something for open 
> ham use.
> Moe ae4jy

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