CV theory and effects

eric coleridge · Post by **eric coleridge** » Thu Jun 08, 2006 3:13 am

Wow, I can see I've really opened up a can of worms here. I'm going to have to read back through these responces when I'm sober... I just got home... this all seems quite complicated right now...

latigid on · Post by **latigid on** » Thu Jun 08, 2006 7:20 am

ikazlar wrote:+5 and -5 voltages do not have the same phase and opposite amplitudes. They have opposite phases and same amplitudes.

Sorry, you're quite right!

I completely contradicted myself. This is why I do chemistry and not physics! Of course amplitude is an absolute value, here peak to peak it's +5V

Sorry for any confusion.

eric coleridge · Post by **eric coleridge** » Thu Jun 08, 2006 3:21 pm

If I understand this correctly, direct currents which are straight lines and the kind of current that knobs output, as in a knob at "10" outputing a steady 5V voltage, is probably similar to Keyboard voltage output, which is like a quantized knob that outputs discrete voltage amounts, right? So, keyboard Voltage is DC also, right?

I know on an oscillator module, or filter module, you can input DC keyboard voltage or
AC LFO voltage (for instance). So, isn't it true that AC and DC currents are interchangeable on all synthesizers? Not just on the Serge? Or am I getting confused about things again.

I think I've got it now. I don't know of a situation where it would be neccesary for me to consider these principles or to distinguish between AC and DC when using the synthesizer. But I like to have a better idea of what's going behind the controls.

latigid on · Post by **latigid on** » Thu Jun 08, 2006 3:59 pm

Sounds correct to me. Think of an AC signal supplied to somewhere as a modulation source. If you apply a non-modulated voltage, you are giving the module or whatever a direct current, so the controller position is essentially static.

godzilla · Post by **godzilla** » Thu Jun 08, 2006 11:35 pm

I can't understand why the voyagers pan input would be - 2.5 to + 2.5

I you wanted to modulate the pan with an LFO then that would give a positive signal right? (unless inverted by the 251, but even then it would be negative not both)

from what i can tell pluggign an LFO into the pan control would only turn one channel up and down and not cross between them.

and if the lower part of an LFO cycle is what goes into the negative range then how can an LFO that goes between positive and negative, have an effect on a frequency input that only goes from 0 to +5 volts

no no i get it the negative voltage just takes away some of the positve voltage thus rendereing the freq lower by whatever the range of the lfo is set to.

is this right?

so do LFOs output signals from (- 2.5 to + 2.5) or (- 5 to +5)?
I assume that VCOs would have the same voltage range as LFOs

godzilla · Post by **godzilla** » Thu Jun 08, 2006 11:37 pm

Are there any books on control voltage that anyone knows of?

latigid on · Post by **latigid on** » Fri Jun 09, 2006 12:26 am

What if you added a DC offset of -2.5V to a normal LFO?

0 - 2.5V = -2.5V
+5 - 2.5V = 2.5V

That would convert from (0 to +5V) to (-2.5 to +2.5V)

asd · Post by **asd** » Fri Jun 09, 2006 9:21 am

here's an online resource/tutorial type of thing with some info: analog modular synthesis by voltage control

i've started to read through some of it, can't say how good it is overall, but coming from a guitar background it's been useful for me so far. synthesizers.com has some more resources listed on their links page too.

this thread is really informative for me, especially since i just got the cp in the past few days. it's helping me make a lot more sense out of it and think it all through.[/url]

eric coleridge · Post by **eric coleridge** » Fri Jun 09, 2006 1:32 pm

godzilla wrote:I can't understand why the voyagers pan input would be - 2.5 to + 2.5

I would assume that the negative portion is one side of the pan and the positive is the other.

godzilla wrote: and if the lower part of an LFO cycle is what goes into the negative range then how can an LFO that goes between positive and negative, have an effect on a frequency input that only goes from 0 to +5 volts

Only the positive voltage of the LFO will effect the pitch, I think.

godzilla wrote: no no i get it the negative voltage just takes away some of the positve voltage thus rendereing the freq lower by whatever the range of the lfo is set to.
is this right?

If an input only has positive range, it will only be effected in the positive range of LFO wave.

godzilla wrote: so do LFOs output signals from (- 2.5 to + 2.5) or (- 5 to +5)?

Different LFO waves will have different voltage ranges. A triangle wave can be -2.5 to +2.5, but a square wave may be 0 to +5.

latigid on · Post by **latigid on** » Fri Jun 09, 2006 7:11 pm

I read the voyager manual, the VX-351 outputs the triangle wave as +/- 2.5V. The squarewave is different. Other CV inputs take +/- 5V, (LFO rate I think) and some take 0 to +5V. All moogerfoogers take 0 to +5V, but as I said earlier, it may be possible to underclock them.

ikazlar · Post by **ikazlar** » Tue Jun 13, 2006 1:26 am

AC and DC are NOT interchangeable on all synthesizers.

If you apply a DC to an LFO you're basically applying an offset to that LFO. Again think of multiplying a constant number (i.e. a DC) with a signal that changes with regard to time. The result will be a signal shifted up (if DC is positive) or down (if DC is negative).

I am not sure if keyboard voltages (from analog keyboards that is...) are DC. In some synthesizers pressing a key means that a voltage is produced, then passed through a S&H for a short period of time, then passed thorugh an AD converter so it can modulate the oscillators or whatever. I am not sure though, maybe MC knows more.

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