[sdiy] vocoder filters

[rburnett at richieburnett.co.uk]

> Frequency tracking of the voice signal, controlling a blending of the
> lower bands in order to avoid the gaps?

It is interesting that you mention frequency tracking.  I had originally 
wanted to include pitch detection on the incoming voice signal for a 
couple of reasons.  Firstly, if you know the pitch of the incoming vocal 
signal, and you also know the spectrum, you can re-synthesise the voice 
with pitch and/or formants shifted by the Vocoder for harmonizer type 
effects.  Secondly, if you know the pitch period from ASDF or 
autocorrelation, you can easily remove the tonal "voiced" spectral lines 
of the original voice signal with a comb filter to leave a residual 
"un-voiced" noise-like component.  This residual signal could then 
either be routed around the Vocoder and mixed into the final output to 
improve intelligibility, or it could be analysed by a separate filter 
bank to process spectral shaping of an additional un-voiced noise-like 
carrier signal.  But efficient robust pitch tracking isn't trivial to 
achieve though, so it might have needed an additional dsPIC running 
alongside the one doing the Vocoder filter banks.

>> This is what Sennheiser seem to have done in at
>> least one
>> of their Vocoders
> 
> Did they make more models?

To be honest I don't know.  I was giving them the benefit of the doubt 
;-)  I thought I read somewhere that they made specials for Daft Punk or 
something.

> Thanks for some interesting discussion.

No worries.  They were just some thoughts that were left in my mind from 
my own Vocoder experimenting.

-Richie,