[sdiy] Additive Synthesis

[Fernando de Izuzquiza]

Looong time ago there was a good soft for Mac (sorry Jobs alergics) 
that did AS quite well. Only 32 oartials but full control.
There you meet with the control problem. But it was not hard to draw 32 
envelopes.

Anyhow there is a very good software for AS as well as granular etc 
called MetaSynth. You can use color images to define the partials. You 
can get good results. Also with the granular introducing a sound from 
wich it will take the audio pieces and build the new sounds based on a 
picture. It has many other features of course.
I had a great time painting and then synthesizing. You can get very 
expresive music out of it, both micro and macro time.

Another way is to use a synth library like csound and use a program 
like CommonMusic to read algorithms and produce the score file. You 
define a "behaviour" and CommonMusic calculates all the little events 
for your "instrument" (additive in this case) for csound to produce the 
final sound
You can build whatever high level control interface this way (not GUI, 
but interface after all)

I did this kind of music work for some years.
Now I don't like using computers for music making, so I try to build an 
analog synth (hehe, back to topic)

Best regards

Fernando


 > De: "Batz Goodfortune" <batzman-nr at all-electric.com>
 > Fecha: Wed, 23 Mar 2005 12:28:13 +1030
 > Para: synth-diy at dropmix.xs4all.nl
 > Asunto: Re: [sdiy] Additive Synthesis - Wendy would say it works...
 >
 > Y-ellow All.
 >
 > At 07:09 AM 3/22/05 -0600, Bill Felton wrote:
 >> I'm a bit surprised no one has mentioned Kyma yet -- it can do live
 >> analysis/resynthesis, with real-time spectral modification.  Pretty
 >> rich set of additive and quasi-additive approaches and some 
interesting
 >> presentations of controls.
 >
 > Actually I did in passing as it happens.
 >
 > Ed asked (off list) why the K5K is close but no banana. And while I'm
 > addressing that, it also sieges nicely with the GUI vs complexity 
thing. So
 > I'll kill them both with a tiny drop of vitriol. Strong stuff that 
vitriol
 > by all accounts.
 >
 > You'll have to forgive my lack of intimate knowledge of the K5K for 
the
 > sake of argument. It's been a hell of a long time since I used one so 
I may
 > have numbers and names wrong. Feel free to nit pick if you wish.
 >
 > Kawai actually released a small bit of software which tried to do 
Fourier
 > re-synthesis but it wasn't very good. Actually useful but way short 
of the
 > mark. Mainly because of the lack of control over the partials. There 
are
 > something like 100 oscillators per voice. Each one has it's own 
envelope
 > generator but they are way to simple. Being only ADSR types. Each 
partial
 > has a fixed relationship to each other which means that if harmonic 
content
 > doesn't fall neatly into this relationship then bad luck. And from 
memory,
 > there is no control over individual partials from LFO sources or 
other more
 > universal EGs etc. Although, I think there's some kind of grouping 
which is
 > mildly useful.
 >
 > At best, the Kawai editor lets you grab some characteristics of the 
sound
 > you're trying to translate but a great deal of post work is needed to 
make
 > it sound anything but "THIN" I'm not saying this isn't useful because
 > within this complex structure you wouldn't dream of starting a patch 
from
 > scratch. (I know, I spent all day once trying to program a few 
patches into
 > the thing.) But however useful it is, re-synthesis it aint.
 >
 > There are lots of ways to break down sound into useful byte-sized 
chunks.
 > MP3 for example, uses a psycho-acoustic method. Obviously the goal of 
MP3
 > is quite different and doesn't lend it self to synthesis. Although 
I've
 > often wondered why could be done with that kind of psycho-acoustic 
modeling
 > synthesis wise. I'll leave that for another day however.
 >
 > MP4 uses a whole bag of tricks to get massive reduction in audio size 
and
 > one of the main tricks is re-synthesis. And here, it's aim isn't all 
that
 > different except that it's designed for streaming. The language of MP4
 > audio is called SAOLC. (pronounced sale sea) It's based on a cross 
between
 > CSOUND and a MOD/TRACKER player. I'm too tired to go into this and I 
don't
 > want to sound like I'm big-noting myself but some 5 years before 
SAOLC was
 > even embryonic, I worked for a sound card company and we were 
developing
 > something remarkably similar. The point being that a MOD/TRACKER 
system is
 > yet another way to break down audio into partials and resynthesisze it
 > later. And you get remarkable quality for a comparatively tiny amount 
of
 > stored data. The reason I'm covering this background is that it 
should be
 > noted that rather high quality playback can be achieved from layers of
 > rather low quality stored data.
 >
 > To effectively use additive re-synthesis, there needs to be lots of
 > partials. Each one needs more than you're average ADSR but less than 
a full
 > 16 bit wave form. However the EG needs to resemble something like a 
wave
 > form. It would be unipolar however and could be quite low in word 
size. Say
 > 8 bit. And maybe as few as 256 samples. You could perhaps draw the 
envelope
 > on-screen with a light pen like the old Fairlite.
 >
 > Using the K5K as a model, that would require about 25K of amplitude 
data
 > per patch. It would be derived initially at least, by a fourier 
transform
 > from an original sound. I also suspect that you could do with having 
some
 > pitch variation of the individual oscillators in a voice as well. So 
that
 > the harmonic relationships are not static. Just how un-static they 
need to
 > be I'm not sure at this point. It would also depend on how frugal you 
have
 > to be with your "Computational resources." It would be nice to have a
 > similar EG arrangement for the pitch relationship of each partial 
similar
 > to the amplitude relationship. However it may turn out that you can 
get
 > away with much less.
 >
 > So at the base of the system you have a resynthesis engine that can 
take
 > any recorded sound and resynthesize it with a high degree of 
faithfulness.
 > You could then mess with each of the 100 odd partial envelopes and 
tweak
 > them painstakingly but there's another way.
 >
 > You take a layered approach. And this is something Kawai did get 
right at a
 > fundamental level with the K5K. You could start with one big, 
throbbing red
 > knob on the front panel. With "Phat" at one end and "Suck" at the 
other. if
 > you like. Like an Equalizer reduced to a single knob, you could have 
it max
 > out all the odd harmonics at the "Phat" end and kill them off at the 
"Suck"
 > end. Underneath that you might have other knobs assigned to groupings 
of
 > parials that could shift them in amplitude or pitch. Underneath that 
you
 > could have a series of universal EGs that do much the same thing but 
with a
 > transient. Underneath that you might have a bunch of LFOs which can be
 > assigned to groups of partials. All the way down to control of each
 > partial's envelope it self. And of course, a bunch of universal EGs to
 > control the over-all transient of the voice etc.
 >
 > The degree of control you use depends on how much tweaking you think 
the
 > sound needs to achieve what you're after. You may find that making it 
suck
 > a bit more gives you what you want. That dulcet BBD tone for example? 
On
 > the other hand, you may be trying to introduce the bowing effect of a
 > violin sound. In which case you might have to adjust a universal 
pitch EG
 > to give you the proper pitch transient. You may find that the upper
 > harmonics of the sound need squashing over time so you could apply a
 > tweezing envelope to partials 50 thru 100. Perhaps a parameter that 
allows
 > you to increase the effectiveness of this tweezing EG to progressively
 > higher partials. All without ever having to have touched the original 
sets
 > of EG data.
 >
 > Since it's mainly all about the control of the amplitude of a harmonic
 > series, your GUI can simply be innovative ways to tweeze the original 
EG
 > data. From the very simple to the very complex. The point being that 
if
 > you're re-synthesis engine does the business in the first place, then 
it's
 > up to you as to how complex or simple you tweeze it.
 >
 > In fact, what the hell, you could make that whole process modular.
 >
 > Anyway, I'm too fried to do a summery right now but I think I've 
addressed
 > the issues asked of me. Except to say that. yes, Re-synthesis is too
 > complex at a stick and rudder level perhaps but we're way beyond that 
these
 > days. I would hope anyway.
 >
 > Hope this helps.
 > Be absolutely Icebox.
 >
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 >
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