[sdiy] Anyone built the ELEKTOR VOCODER?

[Anderson, Robert O]

How about hacking an already existing stereo
equalizer?  You just need to disconnect
the filter bands from the common buss,
add diode and cap DC converter to input filter bands, 
and insert VCAs on the output filters.  Add a sibilance filter and noise
source if desired.  This may not 
be as much fun or controllable as a scratch built one but it would save
time.  Plus you could experiment
with emphasizing specific bands for added effect since
each in and out band has a separate control.  It's 
analog.

Regards,
Bob Anderson

-----Original Message-----
From: Rick Jansen [mailto:rja at euronet.nl]
Sent: Tuesday, January 30, 2001 10:32 AM
Cc: synth-diy at node12b53.a2000.nl
Subject: Re: [sdiy] Anyone built the ELEKTOR VOCODER?



> > 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