[sdiy] Speech synthesis chip

[Richard Wentk]

At 22:43 16/09/2003 +0000, jbv wrote:
>Richard,
>
>Thanks for your suggestions. Actually I already knew all the
>techniques you describe, and I think that each one would produce
>a different result, would have a different "sound quality"...

Indeed.

>For instance, for a pure "singing voice" synthesis, additive synthesis
>can be an attractive solution (realtime control of amp & freq of a set of
>partials is quite feasable with a DSP), although I've used the CHANTTh
>program and I know that things aren't so straightforward...
>OTOH for vocal sound processing, the use of formants makes more
>sense...

You can get better results with either FOF or LPC in Csound. Both are still 
a long way from a plausible singing voice though.

>BTW I'm not sure that "storing/sequencing the control signals created
>by the analysis bank in a vocoder will probably give better results" :
>I have designed / built a 30 bands analog freq analysis that converts
>each channel ouput into a MIDI ctrl signal to be stored on a sequencer,
>and the data I get are somewhat different & less accurate than with
>a phase vocoder...

Well of course. You can't compare something with 30 bands to something with 
1024.

>  Of course, this is mainly due to the different
>analysis resolution, and this is the point : using VC-BPF as formants
>gives more degrees of freedom in parameter settings than a vocoder :
>central frequency, bandwidth & Q can be set / modified independently
>and smoothly for each band...

It also introduces a set of complex phase relationships which makes the 
whole thing far harder to control than you might think.

Don't forget a BPF has a phase response as well as a frequency response. 
Whether you put BPFs in series or use them in parallel, you'll get 
'interesting' phase effects which sound nothing like real vocal formants.

I know because I tried this for my first year uni project, and it didn't 
work. :-)

Yamaha have been threatening to release a digital vocal processor which 
resynthesises an input voice and gives it a new character for a while now. 
So far as I know it hasn't actually been released yet.

I'd be very surprised if you get something that sounds much better than a 
good vocoder using purely analogue technology.

Richard