[sdiy] Anyone built the ELEKTOR VOCODER?

[Rick Jansen]

> > Also, can someone address this question for me: 30 channels at 1/3
> > octave sounds very impressive, but is it necessary? I would think you
> > could have closer spaced channels (1/3 octave) in the frequency range of
> > the human voice plus some harmonic multiples, and have them 1/2 octave
> > spaced outside of that.

Aha, here surfaces an old project I still intend to do, and already bought
chips for, 6 years ago or so: National Semiconductor has (had now, I think) 
the LMF380, a switched capacitor filter chip that you can cascade to build
1/3 octave filterbanks, like for spectrum analyzers. Ech chip has 3 1/3 octave
filters. 

My plan was (is) to at least build a filter section with it and see if 
vocoder-like effects are possible, or else turn it into a spectrum analyzer. 
(The LEDs necessary for a hardware spectrum analyzer add up to quite an amount 
actually!)

For switched capacitor filters you need to do anti-aliasing filtering if
you plan to use the filtered signals for audio after filtering, else you'll
get a lot of digital noise.

Cheers,

Rick Jansen
-- 
Web: http://www.euronet.nl/~rja/
email: rja at euronet.nl