[sdiy] Famous Fixed Filters - FFF PCB ?

[Jorn Bilse]

Hi Juergen, I would buy such a board, I've been wanting a really good preset 
formant filter (like one based on the VP-330) for a while with say a rotary 
switch to select preset formants, for example; "Ih", "Eh", "Ah", "Oh", "Uh", 
"Mm". A really useful and interesting feature would be if it was possible to 
"crossfade" between two adjacent formants with an LFO, it would be a kind of 
Human Phaser/Resonator :)

A classic Combo organ filter you might also consider would be the one found on 
the Yamaha YC-45D, it's controlled by only one potmeter labelled "Bright" 
(upper) and sounds like there's some bandpass plus a bit more going on there, 
the Yamaha manual describes it as follows "...continuously variable to provide a 
hard string-like tonal balance or any shade down to a flute-like effect" (please 
forgive Yamaha for the japenglish :) The mighty YC-45D is of course the organ 
used by Rick Wright on Pink Floyd's Shine On You Crazy Diamond, it's responsible 
for the big organ part of that pad sound (which was layered with a Solina). I've 
played around with the Bright lever quite a bit and in it's mid position you get 
that almost Sitar-cum-Orchestra-like drone sound which you can hear on that 
particular track. Now imagine if you could layer this in parallel with a VP-330 
based formant filter. Run the signal through your JH Triple Chorus and you'd 
have lush analog Choir and Orchestra frequency response all in one.
Loscha posted a nice scan of the service manual in July 
http://www.loscha.com/ybb/YC45D_service_manual.pdf

Another keyboard with some very interesting preset filters are Korg's PE-2000 
(also known as Poly Ensemble S in the US), the Choir presets are especially nice 
and "dark", and very 70s.

Regards
Jorn

----- Original Message ----- 
From: "JH." <jhaible at debitel.net>
To: <synth-diy at dropmix.xs4all.nl>; "analog heaven" <analogue at hyperreal.org>; 
"MOTM List" <motm at yahoogroups.com>
Sent: Saturday, November 24, 2007 6:47 PM
Subject: [sdiy] Famous Fixed Filters - FFF PCB ?


Hi -  I've been thinking about PCB projects for 2008.

What dou you think about a collection of "Famous Fixed Filters"?

I think fixed filters are much underrated. Sure, the first thing you need in
a synthesizer, is a variable filter - a VCF. Several VCFs, actually. The
next step are fixed filters like filter banks, graphic and parametric
equalizers, for formant shaping.
But then there are the "preset filters" that have been optimized in ensemble
keyboards, electronic organs, the Polymoog, the Vocoder Plus, you name it.
These filters can be emulated with parametric EQs to a certain degree, but
it would still be nice to have the original filter, in dedicated hardware,
with all their complexity, all their special overload behaviour, all their
character.

But there's a problem:
A few years a go I built a rackmount FX to emulate the Human Voice filters
of the Roland Vocoder Plus VP330.
This is an example for such a filter - but IMO it's not worth to make a
dedicated module for this. It's a waste of front panel space to make a
dedicated module for such a small filter circuit.

So I had the idea to combine many such fixed filters in one module.

Right now I try to find out how many "famous" fixed filters I can put on a
single 160mm x 100mm PCB - and which filters are your favorites.

The Polymoog comes to mind.
All kinds of Formant filters in electronic organs.
A "manual" filter like the SH-5 BPF.
...
Anything that needs a minimum of front panel controls and has a lot of
character.

Let me know what filter you would like to see included.
And if you're interested in such a PCB at all.

The idea is to offer a board for 27.00 Euro with all the filters on it, and
then allow various configurations:

(1) Each filter may have its dedicated input and output jack.

(2) You have one general input and output, and a set of switches, or a
rotary switch, to choose your favorite fixed filter.

(3) You could also connect potentiometers to each filter output and mix them
all together.

(4) You could have normalized input and output jacks, to use certain filters
separately, and still mix some of the others together.

(5) You could feed different waveforms into dedicated filter inputs, and
then mix the outputs.

(6) or any other combination that comes to mind.

Let me know what you think about this idea.

Would you buy such a board?
What classic filters would you consider mandatory in such a collection?

Looking forward to hear from you!

JH.

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