Cgs synth

I am still getting my flippers wet with the diy thing.I have a
question.

If I calculate frequencies and vary the resistors of the inputs will
I be able to mix (add and subtract)different frequencies of the
inputs?I don't know what kind of effect this will have but I figure
it could be interesting.

Or is this a stupid idea.

Thanks for bearing with a newbie

Phil

Mixers are concerned with amplitudes (voltage) only, not frequencies.
Whatever frequencies go into the mixer will come out. You may be
thinking of the treble, mid, and bass controls on some commercial
mixers. These are actually filters added to mixer. The CGS megamixer
does not have this type of filtering feature.

-Richard Brewster

Phil wrote:

In the audio world, a "mixer" is a voltage adder. It has no real affect other than to combine
two or more signals into one signal path.
In the world of radio, a "mixer" is a voltage multiplier, which has the effect you describe.

In a synthesizer, we have the 4 quadrant multiplier
(balanced modulator, or ring modulator), whose output is the sum and difference of the
frequencies fed into it. They are very similar to the "mixer" used in fm radio.

The effect is often used to get bell or gong like sounds.

Jeff

----- Original Message -----

Okay I understand amplitude is affected
but in a 1 volt/oct synth by varying the ressistors will I affect
frequency?


I appreciate your help I am just trying to get a handle of the
concept.

Thanks,
Phil

Phil,

Certainly, any attenuator used with CV will result in a different
change rate in frequency of an oscillator that is controlled by thet
CV (inside or outside of a mixer).

For example, if you have a CV signal that you are using to control an
oscillator and you want that CV signal to have less imnpact on the
oscillator frequency, an attenuator (like that in a mixer) will do
that for you.

Are we getting close to the answer you are looking for?

Larry Hendry

Yes I am understanding, any mixer will just control amplitude of
whatever signal or CV sent to it.

With the megaMixer using noninverted and inverted ins can I actually
get an adding and subracting of frequencies? Similar effect as the
cancellation frequencies by sending the same signal to inverted and
noninverted?
and what will the offset get me?

Phil

Phil,
The megaMixer can process 2 types of signals: 1, audio; 2, control votages
(CVs). There is a *big* difference between them. So, which are you asking
about?

When using the megaMixer to process of audio signals, the answer is "No, you
can't really do what you want." (Unless you are also using a filter. See ***
below)

When using the megaMixer to process CVs... wait, first let me explain
something: A standard VCO responds to the pitch CV at a 1 volt per octave
ratio. The pitch CV coming from your keyboard or your MIDI-to-CV converter
is going to meet that same 1V/oct specification. We agree on that, right?
Okay. Now, you can use a mixer to adjust the levels of multiple CVs; the
mixer will then add (or "sum") those CVs together, so that you have one CV
at the mixer's output. You can then drive your VCOs with that CV.

Examples:
1) Suppose that your VCO has only one CV input. You can mix the standard
1V/octave pitch CV with the output of an LFO to cause vibrato. You will need
to attenuate the level of the LFO using the mixer's controls. You would
*not* want to adjust the 1V/octave CV, in most cases.
2) Say that you'd like to play with quarter tones, that's where there are 24
notes per octave instaed of 12. How? As above, you patch the pitch CV into
the mixer. This time, however, you adjust the mixer's level control so that
you get half the voltage coming out. 1V in produces 0.5V out; 3V in produces
1.5V out; etc. Some people like to use a voltmeter for this kind of thing.
(By the way, a simple attenuator can do this -- you really don't need a
mixer for this.)

I hope you get the idea, which is that you can make VCOs produce different
frequencies by messing with the CVs that control them. Each VCO will only
produce one frequency at a time, though.

*** I mentioned filters, so here's more on that. In fact, people were
recently discussing this on some other list (probably Analogue Heaven). Run
an audio signal through a lowpass filter or VCF. If you add the original
signal and the lowpass output you will get what you would expect at the
output. But if you invert the lowpass output and add it to the original
signal you will get a highpass output, because the inverted lowpass signal
cancels out the low frequencies. This works perfectly in theory, but may not
work so perfectly in practice! :-) It depends on your equipment.

I hope this helps a little.
--
john

----- Original Message -----

--- Phil <pditullio@...> wrote:

> With the megaMixer using noninverted and inverted ins can I
> actually get an adding and subracting of frequencies? Similar
> effect as the cancellation frequencies by sending the same signal
> to inverted and noninverted?

Phil, if you send identical signals to both an inverted and non
inverted input, the effect should be near cancellation. But, what
does that buy you? The signlas need to be exactly 180 degrees out of
phase, so you cannot really use a cancellatiion effect except with
identical signals. and if 1-1=0 how is that any better than 0+0=0

> and what will the offset get me?

That mixes DC to the processed signal. Perhaps you have a signal
that is 0-10 volts and you want it to be +/- 5 volts The offset
allows you to do that.

Larry




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Larry,

> Phil, if you send identical signals to both an inverted and non
> inverted input, the effect should be near cancellation. But, what
> does that buy you? The signlas need to be exactly 180 degrees out

of

> phase, so you cannot really use a cancellatiion effect except with
> identical signals. and if 1-1=0 how is that any better than 0+0=0

As I get close to 180 degrees won't,an identical or signal with
similar freq., get a kind of filtering(subtracting) of freq?If so I
am wondering if this might be a pleasing or useful effect.

> That mixes DC to the processed signal. Perhaps you have a signal
> that is 0-10 volts and you want it to be +/- 5 volts The offset
> allows you to do that.

Thank you that was helpful

Phil

John,


Thank you that really helped me with getting a handle on the theory
of this mixer.Your examples were very clear.

Phil

--- Phil <pditullio@...> wrote:

> As I get close to 180 degrees won't an identical or signal with
> similar freq., get a kind of filtering(subtracting) of freq?If so I
> am wondering if this might be a pleasing or useful effect.

Not really. The other signal would have to be exactly equal and
opposite. If you tried to say mix in 500 Hz inverted signal thinking
you might cancel out the 500Hz component of a composite signal, you
will be disappointed.

The relation ship between the inverted and non inverted signal is 180
degrees. A reversing attenuator varies from full amplitude at
non-inverted phase to full amplitude at 180 degrees reversed passing
through zero and only changing the phase entirely at the zero cross
point. It is not a sweep around a 180 degree radius with phase
angle.

Larry





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Thanks Larry,

Sounded good in theory.That was the essence of my original
question.You have been very helpful.

Phil