[sdiy] An Elementary Question: Synths vs Organs

[Bob Weigel]

Matthew Smith wrote:

> Hi Folks
>
> Where do organs start and synths end, and vice-versa?
>
> I would like to exclude modern, all-digital gear from this discussion 
> as such things probably muddy the waters in this context.
>
> The impression that I get is that an organ generates all the tones at 
> once via a top-octave generator, divides them down and then adds them 
> to a mix as notes are activated.

Some Organs (both home, and combo as well as some early piano type 
keyboards like Roland EP10) don't use a TOS or TOG if you prefer.  Some 
use individual tuning coils for the 12 tones of a high register.  Then 
divide those down.  The TOS greatly simplified the whole scheme of 
things and they're all dealing with square waves anyway so the only 
advantage of this is that you can do various tunings which is nice.  If 
everything is in repair these coil oscillators are usually pretty stable.

> Then, with a synth, we have one or a number of tone generators* of 
> definable pitch with no fixed note assignment - this being dynamic 
> when notes are activated.


Many of the early monosynths actually also use divide down.   The 
advantage in a monosynth is it gives a pallette of frequencies that can 
be added in various amounts to create approximations of different 
waveforms that cant hen be filtered to simulating other waveforms like 
sawtooth.  Eg. the synths with presets would do this and each sound  is 
constructed by selecting a different fraction of each footage and 
routing it through different filters or like that.

But what makes something a synthesizer is..whether it has significant 
facilities to control the type of sound that is made.  Many of them like 
those with a lot of presets also have basic controls for filter opening 
and resonance as well as some envelope controls  etc.  The minimoog and 
other more purist analogs generate the waveform in an analog process 
rather than adding square waves.  And this opens the design up to a lot 
of potential imperfections but..like any well crafted instrument....this 
reality became the strength of the minimoog and others of that type.  
The Korg Sigma is an interesting melding of a 2VCO monosynth with a lot 
of preset tabs.  But it's a synthesizer because every tab has it's own 
little tweak knob.  Some for attack/release combination.  Some for 
filter opening.  And because you can actually mix ALL of the waveforms 
(though you can't set their intensities, unfortunately.  I'd love to mod 
one so you can some day) that combined with the tweaks on each one make 
it a very different kind of machine.  Along with the fact it has an xy 
joystick for both bend/modulation (AT mods also with a switch to select 
how) AND for controlling the High and low pass filter simultaneously! 

Anyway there are also many full poly synths using TOS and divider 
technology which are considered synthesizers because they have 
facilities to control aspects of the sound worth mentioning.  The Moog 
Polymoog has a front end similar to many organs.  But each note has it's 
own VCF/VCA chip and these are programmed via resistor packs which could 
theoretically be exchaged for digitally controlled resistances I suppose 
:-)  I've thought of doing this to mine too and having a s/w editor for 
it maybe.  But anyway it's a fully polyphonic preset synth since 
changing resistors on the fly is hard.  But it also can go into a manual 
mode where you can vary the parameters of the one Moog filter that is on 
board and envelope and dynamics and so on.  Plus there are resonators in 
a separate mix and 'mode cards' which are filters set up to create 
brass, string etc. voicings that are in a separate mix...and then the 
straight mix fight off the square/saw ranks.  And the ranks can be 
modulated from the front panel also.  And even when not in the manual 
mode you can opt to edit the LFO's that modulate the ranks manually and 
so on.   Organs, especially combos, often have vibrato amounts but we 
don't call them synths because it's just so rudimentary and doesn't lend 
to creating sounds that are very out of the ordinary.  Three separate 
LFO's starts to become a formidable area to consider at least on a 
machine in this case.  And footages/wave types can also be selected 
manually of course and the dynamic settings and resonator setups.  So 
that's quite a bit of sound tweaking ability even when the full poly 
mode is selected.  But then if you select the moog filter option you 
have a paraphonic synth we call it. Multiple notes sharing the same 
synthesis facilities.  Paraphonics give the player an initial 
challenge.  They have to learn to play something that either triggers 
the filter when all fingers are lifted, or retriggers the filter every 
time a note is hit (single or multiple trigger they call it on the Korg 
Delta which can actually switch this for both the synth and string 
section).  And these different types of paraphonic behavior can be used 
to create various kinds of grooves actually that a truly full polysynth 
can't do.  The releasing of all notes in the single mode particularly 
because another emphasis point in the music where continuing to hold 
notes cause the impact of successive notes to diminish in the case of a 
decaying filter envelope for instance.

So anyway check out the sounddoctorin.com global synth link.  I do a lot 
of jabbering about different architectures on there. -Bob

>
> Is my thinking correct?  If so, here's a bonus question: what do you 
> call an instrument where each note has its own dedicated tone 
> generator - other than a pain to build and even more of a one to get 
> in tune ;-)
>
> Cheers
>
> M
>
> * I'm using the term 'tone generator' to apply to oscillator(s), 
> filters, VCA, all in one lump.
>