Questions

Harry Bissell harrybissell at prodigy.net
Sun Nov 7 23:14:52 CET 1999


Comments included::

Christian Baumann wrote:

> Hello to all,
>
> thank you very much for your information!! :-)
>
> I looked around in the websides you recommended and it´s quite a flood
> of information for me and I don´t know where to start.
>
> I try to "repeat" about the necessary itmes of an analog synth, so far
> as I understood ( please correct me if I am wrong.....and I thing there
> is something wrong ).
>
> First I need the VCO´s for creating the waveform´s , like sine, triangle
> and propably rectangle and pulse.

VCO are SOURCES
Sawtooth is #1 has all harmonics possible (Brassy)
Fundamental + 1/2 second harmonic + 1/3 third harmonic + 1/4 fourth
harmonic....

Square has only odd harmonics (Reedy)
Fundamental + 1/3 third harmonic + 1/5 fifth harmonic... (fractions may not
be quite right)

Triangle (Flutey ???) Same as square... odd only but falls at 2X the rate
Fundamental + 1/6 third harmonic + 1/10 fifth harmonic (fraction might be
off a little...)

Sine (pure) (not too useful except as mod source... filters don't work on
sine waves)
Fundamental only...

Pulse... is missing harmonics related to pulse width...
25% pulse is missing fourth, eighth etc...
75% is the same as 25%

Noise is a source too (think between radio station Hiss...)
Good for Drums, cymbals, wind, surf etc...

Modulating the pulse width (PWM) gives a flange like sound...

>
> Then  VCF´s to filter them and finally a VCA to amplify them.

VCF and VCA Are MODIFIERS they change the harmonic content and the
loudness...

>

LFO and ASDR are Controllers (as is the keyboard...)

LFO gives Vibrato (freq mod) Tremelo (amplitude mod) and other control
functions
ASDR sets filter and amplitude shapes...
Keyboard tells which note... and whan to start and stop
Sequencers play pre-programmed control  patterns.

>
> Somewhere there must be the LFO´s for a kind of  bass for example, but I
> don´t know where to put them in. Then there are the ADSR-Controlsliders.

Yes the power supply must be good... but better designs of synth modules are
not too sensitive to voltage change... (thats what makes them good designs)
Buy a power supply... you will not be sorry. Get a Linear supply...
switching supplies can induce noise into the synth circuits and screw them
up in subtle and hard to find ways...

>
> Finally a good power supply, it must be very good, I think, because if
> the voltage drops around some milivolts, the note will be out of tune,
> or ??
>
> Then, I´ve got still some questions:
>
> Are the sine, triangle rectangle basic waveformes, where it is poosible
> to mix all thinkable sounds like a strings or piano ??
> I compared it to the primary colours red, yellow and blue, where you can
> mix all thinkable colours.

The basic VCO waveforms DONT sound like piano etc. They exist because they
1) Have Harmonics so the filters can work on them...
2) They are easy to generate with simple circuits...

There are VCO's that have actual waves from Piano etc SAMPLED (digitally
recorded) into them... They sound much more like the real thing... They
might be DCO (digital controlled oscillator...) or if they record the actual
shape of the wave (attack, decay...) then the instrument becomes a Sampler
(think tape recorder) and not a Synthesizer...

>
> Thus you may need three VCO´s, for creating the waveforms, VCF to soften
> a particular waveform and then the VCA to get a stronger signal. Could
> be that a structure of an anlog synthesizer ??

One VCO is necessary (Like the TB-303 bass line)... Two is better in most
cases (now the VCOs can be set to "beat" giving a nice "swooshy" sound, or
at octaves or fifths for more fat sound... Three (like Minimoog) could be
Two oscillators for pitch + 1 LFO, or all three VCO for extra -fat sound...

>
>
> What happened if I would take more VCO´s ??

The sound gets more and more complex... and harder to keep in tune and
control... Basically more is BETTER. You don't have to use all at once...

>
>
> The most personally synth´s which I have found in the internet are a
> kind of "box" and controlled by a midi-keyboard. Is it possible to build
> a synthi or has somebody in the list built a synthi which has it´s own
> keyboard ??

Yes... TomG cookbook has some DIY keyboard circuits... but beware!!! They
are for the 1V/oct type VCO. The "Fatman" will not work with this
standard...

>
>
> I looked at www.paia.com for the Fatman, and it sounds good. But if I
> would build this synthi, is it possible to upgrade it, like adding some
> more VCO´s ?

> There are many sites for Fatman Mods !!! Scott Gravenhorst (sp?) comes to
> mind.
>
> I read about the different types of synthesizer and I liked very much
> the modular synthesizer, because of the inifnte possibillities of
> creating sounds. Is this also possible with an analog one ?
> Has somebody build such a modular type ?

Probably most people on the list have modular synths... They are easy to
build and modify because they are (duh!) Modular. The down side is the
cables and plugs etc. can get expensive... and you need a few yards of
spaghetti (wire) just to get the most basic sound...

The non-modulars assume you want to make "conventional" music sounds... so
they are easier to play but much less flexible, and less expensive... If you
just want a "Bass" sound the TB-303 (see TB-3030 clone on list) is the
easiest way to get it... But if you want a sound that is entirely new... use
the Modular...

(I'm building a new modular myself... but if I play live I use a
"normallized" synth like a Minimoog. You can't tell the audience... "wait
for a half hour while I get the next sound ready...)

Any More Questions
(yeah... LOTS ???)

:^) Harry

>
>
> Sorry that I ask you so much, but I´m very curiouse about this.
>
> Christian




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