Understanding 1V/Oct

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ipassenger
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Understanding 1V/Oct

Post by ipassenger »

So something that has spinning around my brain is this 1V/oct business.

If a module has a 1V/Oct input, is it expecting a signal that swings from 0V - 7V (so therefore 8 octaves) or -5V to 5V (so like 11 octaves) ?

When I control my osc in my modular from my waldorf pulse they seem to be limited to around 8 octaves, so is that the module cutting off its control range (clipping the control range) at the 1V/Oct input or is it my pulse? or both? Just trying to better understand what is happening. What do 1V/Oct inputs normally expect in terms of actual voltage range? Furthermore is C1 the standard minimum midi note when converted to a control voltage?

Also my pulse does something odd, I think the swing of the CV2 voltage ranges from -2.5V to +2.5V, so if this is set up to be controlled from say a modwheel, the CV goes negative at 0 CC value.

I take it this is not normal for Midi to CV conversion of control voltage, they usually go 0v-5v with an incoming range of 0-127 midi CC value?
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Entrainer
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Re: Understanding 1V/Oct

Post by Entrainer »

ipassenger wrote: If a module has a 1V/Oct input, is it expecting a signal that swings from 0V - 7V (so therefore 8 octaves)
0V-7V is 7 octaves.

Modules with a 1V/OCT input are not "expecting" anything really (except
voltage). You can feed them DC or AC, even audio-rate waveshapes like
sines or squares.

Control really depends on your midi-CV convertor AND the range an
oscillator can accurately track. If your midi-CV convertor outputs a 10V
swing but your oscillator can only track 5Vs, that's one issue. The other
is if your oscillator tracks 10V and your midi-CV convertor only allows for
a 5V swing.

-2.5V to +2.5V is a good pitchbend control where 0V is the current pitch
of the oscillator. Then you'd pitch down 2.5 octaves and up 2.5 octaves.

The trick is knowing the range so you can tune your oscillators. I first
patch the Midi-CV convertor in, then play a keyboard searching for top
and bottom range in response.

When you tune, you'll often have to make offsets in your mind due to
available Midi-CV range (ie, tune middle C an octave or two down for bass, etc)
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Post by Ranxerox »

A typical sequencer might output -5v - +5v, i.e. covering a ten octave range. So if you calibrate an oscillator to be at middle C with 0 volts on the 1v/oct input, then your sequencer would give you 5 octaves either side of that (depending on how well your oscillator tracks ofc).
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Post by rockwoofstone »

A simpler way to look at 1V/Oct is simply that no matter the voltage source you're feeding into the module, if you increase it by 1V, the output "note" of the oscillator will increase by 1 octave, irrespective of where it started from. If it's a very fast source (such as another oscillator), then this will just happen really quickly. From there, you get into FM synthesis, as the rapid changing of the frequency starts to create extra harmonics, and a whole world of fun opens up. Anyway, in summary...

Increase source by 1V = raises the note 1 octave = doubles the frequency
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Post by daverj »

There is no standard for the full range on a 1v/oct input. Some devices might work with +/-5v, some +/-2.5v, some 0-5v, and maybe even 0-10v. The only "standard" is that a 1v change causes a 1 octave change.
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Post by Dr. Sketch-n-Etch »

I can only speak for the modules I've designed personally with 1V/octave inputs (Dixie, Rubicon, Doc Oc, Korgasmatron, uVCF, a few others) and those designs that I've investigated as part of my learning curve...

1V/octave inputs are (virtually) always current inputs to opamps set up as inverting amplifiers. Hence, there really is no limit to the voltage that you could feed in, since it is simply converted to a current through a resistor. The standard resistor size for CV inputs is 100k, so even large voltages (i.e., the 15V rail) will be converted to very modest currents (150 microamperes in that case).

So, how do 1V/octave inputs work? Well, their currents are almost always summed with another current from a panel potentiometer (the tuning knob on a VCO, the cutoff knob on a filter, etc). Hence, given a certain knob setting, then a CV of 0V into the 1V/octave input will do nothing, since it will be converted to zero current across the input resistor -- in other words, there is nothing to add to the current from the panel pot. Any positive voltage will convert to a positive current, and any negative voltage to a negative current. These will add to or subtract from the current from the panel pot to move the pitch accordingly.

Hence, in most systems, CV into a 1V/octave input should be able to move the output up OR down 12 (euro) or 15 (5U) octaves from the panel setting. Of course, most oscillator and filter circuits are not sensitive to that much change. The frequency of most oscillator circuits simply stops increasing above a certain frequency, for example. Also, the entire audio range is really only about 10 octaves, so +/-5V is about all that is required for most purposes.

That's about all I can think of to say for now.
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Re: Understanding 1V/Oct

Post by ipassenger »

Thanks all, I think what I am getting from this is my Pulse is limited to 8 Octaves on its CV out.. I think.

I am going to test it out and see if I can work out its swing based on the offset from a centre point, should be easy enough to work out.

The lack of standards is both fun and confusing. :)
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Post by ipassenger »

Well that is weird it looks like the pulse goes from 0v - 5v on its CV Out 1, pitch out, which makes sense but the CV Out 2, the controller out is set from -1v - +6v! Odd combination. Used the 1v input on an osc and measuring the extreme changes it causes gave me these figures. 8_)
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Post by flashheart »

Nothing unusual about those figures. Pitch CV is normally sent as a positive only voltage, as it's derived from note values. Modulation CVs are usually bipolar as the CV source is more likely to be an LFO / envelope.
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Post by orangehexagon »

Dr. Sketch-n-Etch wrote:I can only speak for the modules I've designed personally with 1V/octave inputs (Dixie, Rubicon, Doc Oc, Korgasmatron, uVCF, a few others) and those designs that I've investigated as part of my learning curve...

1V/octave inputs are (virtually) always current inputs to opamps set up as inverting amplifiers. Hence, there really is no limit to the voltage that you could feed in, since it is simply converted to a current through a resistor. The standard resistor size for CV inputs is 100k, so even large voltages (i.e., the 15V rail) will be converted to very modest currents (150 microamperes in that case).

So, how do 1V/octave inputs work? Well, their currents are almost always summed with another current from a panel potentiometer (the tuning knob on a VCO, the cutoff knob on a filter, etc). Hence, given a certain knob setting, then a CV of 0V into the 1V/octave input will do nothing, since it will be converted to zero current across the input resistor -- in other words, there is nothing to add to the current from the panel pot. Any positive voltage will convert to a positive current, and any negative voltage to a negative current. These will add to or subtract from the current from the panel pot to move the pitch accordingly.

Hence, in most systems, CV into a 1V/octave input should be able to move the output up OR down 12 (euro) or 15 (5U) octaves from the panel setting. Of course, most oscillator and filter circuits are not sensitive to that much change. The frequency of most oscillator circuits simply stops increasing above a certain frequency, for example. Also, the entire audio range is really only about 10 octaves, so +/-5V is about all that is required for most purposes.

That's about all I can think of to say for now.
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Post by BOETTKE »

Does anyone know what the standard voltage range of say a doepfer LFO is, in relation to this question
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Post by flashheart »

Most modules are +/-5v
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Post by rockwoofstone »

The original "standard" for Eurorack voltages is specified here...

http://www.doepfer.de/a100_man/a100t_e.htm

...which provides info on things like LFO ranges, although these values are only guidelines, and as Dieter says later on that page...

"It's just about true to say that anything can be modulated by anything else".
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Post by boombipbass »

So how would you change the note lenght when using a Beatstep with an E350?
Is that only possible on the beatstep or are there more options?

Also an LFO for example the Doepfer 146 or 145 or Peaks are CV LFOs right?
And the SynTech E350 would be Audio LFO?

Just to get this clear for me :)
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Post by paterursus »

BOETTKE wrote:Does anyone know what the standard voltage range of say a doepfer LFO is, in relation to this question
Doepfer's LFOs are all over the map in terms of output ranges. There is even variation within a single module depending on the waveform.
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Post by mirth23 »

boombipbass wrote:So how would you change the note lenght when using a Beatstep with an E350?
Is that only possible on the beatstep or are there more options?
Your question is a little confusing from my perspective. The E350 doesn't have a "note length", per se.

In subtractive synthesis, the note length is typically controlled by an envelope going into the VCA that the audio from your oscillator is going through. The BSP's gate should trigger this envelope (with the pitch going into 1v/oct on the E350). Some envelopes will sustain if the gate stays open, some just do their own thing. You could also just use the gate out from the BSP into your VCA, but it won't sound very smooth.
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Post by mskala »

Dr. Sketch-n-Etch wrote:1V/octave inputs are (virtually) always current inputs to opamps set up as inverting amplifiers. Hence, there really is no limit to the voltage that you could feed in, since it is simply converted to a current through a resistor.
It's worth remembering that that's true of analog oscillators where the current coming from the op amp goes to control the exponential converter. If a digital oscillator uses an ADC to measure the input voltage, that's another story, and there'll probably be a hard limit on the voltages it can usefully accept. For instance, the Hikari Sine seems to stop at 0V input, with negative voltages not lowering the frequency any further.
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Post by boombipbass »

mirth23 wrote:
boombipbass wrote:So how would you change the note lenght when using a Beatstep with an E350?
Is that only possible on the beatstep or are there more options?
Your question is a little confusing from my perspective. The E350 doesn't have a "note length", per se.

In subtractive synthesis, the note length is typically controlled by an envelope going into the VCA that the audio from your oscillator is going through. The BSP's gate should trigger this envelope (with the pitch going into 1v/oct on the E350). Some envelopes will sustain if the gate stays open, some just do their own thing. You could also just use the gate out from the BSP into your VCA, but it won't sound very smooth.
Indeed that is what I wanted to know, thanks :) I have no pro just the beatstep. I can change the gate from 50 to 100 meaning 100 is is a lot of ms of signal and 100 is not so much signal when a pad is made blue(=turned on) on a sequence running.

If I put the beatstep into an envelope and then into the vca(also with the E350 I'd get what I require I guess right? :) That I didn't think of this earlier.. :cloud:
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Post by dComposer »

Just wanted to add this link to Learning Modular's "Matching Octaves" article. It was the Rosetta Stone that helped me wrap my head around all this!
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Post by boombipbass »

mirth23 wrote:
boombipbass wrote:So how would you change the note lenght when using a Beatstep with an E350?
Is that only possible on the beatstep or are there more options?
Your question is a little confusing from my perspective. The E350 doesn't have a "note length", per se.

In subtractive synthesis, the note length is typically controlled by an envelope going into the VCA that the audio from your oscillator is going through. The BSP's gate should trigger this envelope (with the pitch going into 1v/oct on the E350). Some envelopes will sustain if the gate stays open, some just do their own thing. You could also just use the gate out from the BSP into your VCA, but it won't sound very smooth.
Somehow this isn't working. I am using a beatstep cv/out to the mutable peaks trig1 in with enveloppe attack 0 decay 3 sustain 4 release 0 to a intellijel uVCA II cv A input and the Z out of the e350 to the In A input of the uVCA II and the output of the uVCA II to my soundcard but I dont hear anything?

Am I doing something wrong? tried turning all the knobs on the VCA but no succes :(

EDIT: Ah now I understand I have to do that trick with the Gate/out and the CV/Out still going into the 1v/oct.

Sorry my bad, I should read better :hail:
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Post by Sandrine »

I find 5 Octaves ample (thus use primarily + side) for the dynamics of the sound where beyond that the filtering/envelope starts sounding too alternate, i.e. a nice 404 buzz bass line 4 octaves up sounds, well, just like any old square wave type of thing :)
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