[sdiy] Vocoder dumb idea of the night

[Czech Martin]

A 2N order bandpass has N*6dB fallof for higher, lower frequencies.
2nd order means 6dB, 4th order means 12dB. Arround the peak it can be more
due to high Q.

Switchers can serve well for the analyser part. In the synthesis part they
could cause clock feedthrough problems.
In both sections there could be alias problems. After all, they are 
sampling structures.
Perhaps better, if you combine them with a normal 2nd order bandpass
for anti alias/ clock reject.

Some 100 mails before there was a short discussion on vocoder banks
together with some very interesting links.

m.c.

-----Original Message-----
From: Tom Arnold [mailto:xyzzy at sysabend.org]
Sent: Mittwoch, 14. Mai 2003 07:47
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Vocoder dumb idea of the night


I've been toying with an idea for a while, basically ever since buying my
PAIA vocoder and wanting more.  Wanted to bounce this idea off some people
and see how insane I was.

After getting Thomas Henry's NE570 application book and playing with the
chip as both an envelope follower and a VCA, I was thinking of coupling
this with my other new found friend the switched capacitor filter and
making a Vocoder.

Have I snapped?

My reason for using the NE570 is, well, they're cheaper then sand and it
keeps my parts count low.
My reason for using a switched capacitor filter is they are also cheaper
then sand and setting the frequency is easy and can be varied also very
easily.  Drawback I see is unless I want to double up filter ICs I'm
stuck with 4th order, which I think ( and I'm hoping to be corrected if
I'm wrong ) that thats only a 24db rolloff which probably isnt steep
enough for a, say, 20band vocoder., which even being cheap as sand will
start adding up.

Still, I think the parts count even at 4 filter ICs per band would be lower
then I could do otherwise.

I actually started toying with this idea while cloning the Ensoniq ISF-1
and playing with the chip on there, but it wasnt nearly as adjustable
as an SFC.

Sanity check please?

-- 
 ------------------------------------------------------------------------
 - Tom Arnold -       When I was small, I was in love,                  - 
 - Sysabend   -       In love with everything.                          -
 - CareTaker  -       And now there's only you...                       - 
 --------------         -- Thomas Dolby, "Cloudburst At Shingle Street" -