[sdiy] Anyone built the ELEKTOR VOCODER?

[jbv]

Paul Perry :

> >
> For someone like JB who can meet a challenge, I recommend pulse width
> modulated amps. You only need one triangle generator. And, the parts are
> cheap and available (and likeley to remain so.. comparators and switches)
>
> paul perry melbourne australia
>
> warning: I havn't done this myself!! It's just free advice! ;)


Any pointer to articles / schemos about that technique ?




Scott Bernardi :

> Your graphic of the filter response curve with the three staggered fc's
> and the middle one (which is the middle frequency band for the channel)
> running at 1/2 the Q of the two side bands is how you get a "maximally
> flat" response. I understand that, but I'm having a bit of trouble
> visualizing where the bands fall. Could you label your schematic with Q
> and fc values for each filter stage? Maybe even a table (not schematic)
> of your whole vocoder?

More infos (as well as math demonstration) can be found at :
http://perso.wanadoo.fr/jbv.silences/DIY/Vocoder3.jpg

Again, this is a straight translation from an Elektor article about a realtime

spectrum analyzer.

>
>
> 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.

Yes, that makes sense. But my approach was different : my first goal was to
take that spectrum analyzer, add a bunch of rectifiers to it as well as ADC
and
MIDI output, and then record the analysis result as a serie of evolving MIDI
ctrls
on a digital sequencer. Then I thought I could add a similar filter bank +
VCAs
for the synthesizer part and then get a 30 bands vocoder. I can also use the
MIDI
ctrls data (from the sequencer, or from SRAM on the MIDI i/o board that can
store about 30 sec of data) to control the VCAs... And there's also a
voice/devoice
detector whose output data is also recordable as MIDI event... And a diode
matrix
to visualize spectrum (either in realtime, or data from the sequencer) - I was
also
thinking of replacing the diode matrix with a computer screen...

As for MIDI, can you imagine (for instance) sending the MIDI output data from
the analyzer part, processing them in some MAX patch, and then sending it back

to the synthesizer part (or any other analog gear)...

As you can see, this "beast" is meant to be a spectrum analyzer and "spectrum
modulator", rather than strictly a vocoder...

Nevertheless, if you look at the central freqs of the 30 bands, and if you
consider
the spectrum of human voice (roughly 100 Hz to 2 KHz), there's 14 bands in
that
range.

JB