[sdiy] Thoughts on a Polyphonic Synth

[phillip m gallo]

So far i agree with all posts, just not exclusively.

I would argue that you have to conceptualize the synth beyond just being
"polyphonic".   The decision to gang or individualize the timbre and
envelope control has a dependency on the way it's activated.  When a
keyboard, 1 or more approaches or algorithms emerge as how to assign keys to
voices.

If assignment is a "roll-over" (i.e. my JX3P) where next key/next voice
assigns; then the unified timbre control can be quite natural.  This is also
true for key switched TOG/Divider schemes.

If you differentiate and "track" key activations (Highest Sounding/Next
Highest Sounding/.../Lowest Sounding Voice) then individual voicing can be a
more natural assignment. Two voice analog and digital keyboards have long
implemented with hi/lo key differencing.

"Next Key/Next Voice" gets interesting when voices Do Not have unified
voicing.   Each new voice punctuates a melodic figure or a chordal movement
giving it accent and pattern related to the assignment not the figure or
movement. If you roll odd # of voices across a figure of even activations,
rotating accents travels the  line. If you gang control of these voices;
then a melodic movement travels nearly exact timbres so accents and rhythm
attribute more to the figure and the activation.

Using "organish" synths (Lancaster poly/string ensemble/Yamaha DCO
Chips/JX3P/Computer Wavetable) i've integrated in some fashion to analog
gear (from MIDI/micro to shared Keyboard via multiple contacts (Vox
Continental).

Providing "Organish" synths a "descant" and "bass" voicing (Highest and
Lowest sounding notes) using independent mono synths works real well,
especially as a performance synth.  Commonly, either voice only assigns
across the middle of the key manual if the distance (in semitones) less than
it's opposing voice. Each synth is provided  MCV/Gate/Trig.

An alternate assignment is to bind Hi/Lo voices to 12 to 15 key ranges,
translating a key value to sounding within this 8ve or so range.  Either
techniques work well between melodic and chordal playing.  Independence for
voicing is pretty natural for these approaches.

The most voices i've ever dictated the assignment to was 12.  And this was a
cheat (9 Yamaha DCO's  + 3 independent analog synths).  The DCO's Envelopes
only required specification and logical "trigger".    While all where
capable of individual timbral control, most commonly i would assign the
DCO's similarly as a full group or as 2/7 (and again the "2" where outer
voices sounding).  The analog voices assigned as Descant, Middle and Bass
voice.

My latest synth work (if ever finished) implements all control LFO (2)
Envelopes (10) and MCV (4) electronically (DACs).  The envelopes aren't hard
to keep track of and if MIDI, velocity is a great help. You have to spec the
micro in regards to execution rate and the DACs for speed of loading, the
update rate is a great arena for philosophical debate, as is the word width.

regards,
p





-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Antti Huovilainen
Sent: Friday, March 24, 2006 11:41 AM
To: Tom Arnold
Cc: Synth DIY List
Subject: Re: [sdiy] Thoughts on a Polyphonic Synth


On Fri, 24 Mar 2006, Tom Arnold wrote:

> How could you autotune/autoscale a standard sawtooth core VCO?  I suppose

If you're talking about digitally controlled VCO, it's fairly simple.
Typically the error is fairly smooth, so it is enough to measure the
required CV at say, octave, intervals, store those to table and then
interpolate the table to find the real CV output corresponding to virtual
CV.

You can improve it by measuring the table on say startup, then removing
any constant offset and gain. Now you can retune on the fly by measuring
only three notes and then calculating the offset & gain adjustment from
those. The key is that any nonlinear warping is probably not very
temperature dependent so it can be assumed more or less constant.

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
   -- Lt. Cmdr. Ivanova
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