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Author Some beginners questions on waveforms and voltage
sine language
 Hi all, Im hoping to get clarification or confirmation on a couple of assumptions in my head: 1. Audio output from VCO and VCA is AC voltage 2. The "shape" eg sine wave, square wave of a waveform can be viewed on an oscilliscope app or software from the mic input of a phone or computer because it is an AC signal 3. Control voltage is DC voltage and can be measured with a multimeter 4. Control voltages can be negative or positive (like an LFO) but audio level voltage is positive. 5. A full wave rectifier (like is the ES Disting module) can convert an AC audio signal to DC to use as a control voltage so that I could use an audio signal to control pitch of an oscillator. Thanks
diode_destroyer
 I'm a newbie so take this all with a grain of salt but... 1. Audio output from VCO and VCA is AC voltage Sure. But doesn't have to be. For example, you can feed most VCAs a CV (low frequency) signal into its input and therefore have control over the output attenuation/amplification using the CV signal you feed the VCA. 2. The "shape" eg sine wave, square wave of a waveform can be viewed on an oscilliscope app or software from the mic input of a phone or computer because it is an AC signal Sure. 3. Control voltage is DC voltage and can be measured with a multimeter Kind of. Control voltages can be LFO signals (low frequency AC waves). They can also be audio rate AC waves. I prefer to use a scope to look at control voltages because they are usually changing (though slowly, e.g. sample and hold signals, LFOs, etc.). 4. Control voltages can be negative or positive (like an LFO) but audio level voltage is positive. Audio signals are generally also symmetric about 0, so they are just like LFO signals, the swing is both positive and negative. Unless you go out of your way to shift it up by adding a positive DC voltage or something. 5. A full wave rectifier (like is the ES Disting module) can convert an AC audio signal to DC to use as a control voltage so that I could use an audio signal to control pitch of an oscillator. Sure, but of course not required. You can feed oscillators LFO signals (or even audio rate signals) directly in to the CV inputs to change their pitch, but you have an interesting idea here that probably everyone but me already thought about. If, after rectification, you average (or integrate over some period and then divide by the period), then it sounds like an RMS / envolope follower scheme, or envolope detector: https://en.wikipedia.org/wiki/Envelope_detector.
sine language
 Thanks Diode destroyer Actually I just realised, isnt DC voltage stable and AC swings between positive and negative? An LFO is DC but must have a circuit that causes it to do the same? I think im getting confused between voltage and waveforms... Also, are you saying that an AC signal can be fed into CV in of an oscillator to modulate pitch? Thanks Sasha
Risc_Terilia
 I think (for most systems) it's more helpful to think of things as a continuum of signals from pure DC (which can be seen a 0hz [stopped!]) up through your normal LFO type frequencies all the way to audio rate signals. They're all the same thing though really. That being the case yes you can send AC (ie audio signal type frequencies) to a VCA to get audio rate AM (amplitude modulation).
cptnal
 The straight ones are DC and don't sound very interesting on their own, but you can add them to other things. The wobbly ones are AC and you can hear them if they're going really fast. Other than that it's just a matter of plugging one thing into another to see what happens. Such is my collected wisdom. Hope it helps
Navs
 They're all voltages. Some move faster than others, some don't move at all.
mskala
 Navs wrote: They're all voltages. Some move faster than others, some don't move at all.

Yes.

The original posting was phrased as if "DC" and "AC" are completely separate things, but it's really a question of where you draw the line. The physical world just contains voltages, all of which change at some rate. Synthesizer CVs, in particular, are often in a grey area where it makes sense to think of them both as slowly changing DC and as low-frequency AC.
Richie Witch
 Navs wrote: They're all voltages. Some move faster than others, some don't move at all.

Yeah, in engineering terms, this is more accurate. AC stands for "alternating current", not voltage. However, if voltage is changing, current will also change, given Ohm's Law.
Technically speaking, DC (i.e. direct current) would require a voltage that does not change--ever. Offset voltages are probably the closest thing we have to DC. And the voltages coming from our power supplies (hopefully). But here in modular land, we've gotten into the habit of calling just about any signal below audio frequencies DC, which technically is not accurate.

AC is a current that alternates, regardless of the speed of change. DC is a current that does not.

But hey, the point of language is to communicate. Critical thinking requires that we define our terms and agree on them collectively. So sure, slow moving voltages can be considered DC for the sake of our unique conversations.
sine language
 Thanks all. Its starting to make sense Is there a difference in the sound of an oscillator between positive and negtive voltage in 1v/oct input? Does 2v and -2v have the same pitch ? I ask because i have read that control voltages are usually positive voltages...
nigel
 sine language wrote: Is there a difference in the sound of an oscillator between positive and negtive voltage in 1v/oct input? Does 2v and -2v have the same pitch ?

A -2V control voltage will drop the pitch by 2 octaves, +2V will raise the pitch by 2 octaves.

This topic has been covered before - for example, read https://muffwiggler.com/forum/viewtopic.php?t=187212 and https://muffwiggler.com/forum/viewtopic.php?t=32133
cptnal
 sine language wrote: Thanks all. Its starting to make sense Is there a difference in the sound of an oscillator between positive and negtive voltage in 1v/oct input? Does 2v and -2v have the same pitch ? I ask because i have read that control voltages are usually positive voltages...

Think about it - "one volt per octave".
ranix
 I don't necessarily know what I'm talking about but I'm assuming someone will call me out on my BS if I get it wrong: 1. Audio output from VCO and VCA is AC signal (it has a voltage, but that's not what it is). 2. You are absolutely correct. 3. This is correct but remember it isn't just voltage, it's a DC signal. It has voltage, and it has current, and it has some other properties. Sometimes you might need to buffer a control voltage if it slumps or lags. 4. This is correct but you should know that not all modules respond to the same range of voltages. Some modules might not like negative voltage, or some might wig out if you go over +12 or something. There are tools like signal processors you can use to manipulate your signals if you have modules like this. 5. This is technically correct but I don't think it would sound very good.
sine language
 OK Thanks Im a bit confused about oscillator range and pitch control voltage Say I have an oscillator with a frequency range of 10hz to 20khz I would have expected that inputting a 0V voltage into the VCO CV input would play a 10Hz signal from the output provided the octave dial is fully turned anti-clockwise But what would happen if I then input a -15V voltage into the CV input? The oscillator can’t play lower than 10hz, so what would happen?
ranix
 Sometimes the module manufacturer puts a safeguard in to stop it from going below 10hz. Sometimes the circuit is just naturally incapable of going below that (these knobs don't turn past 0). Sometimes the module will produce something called "undefined behavior". That could mean unpredictable things happen or it could mean nobody has studied the behavior under those conditions so you're on your own.
Risc_Terilia
 sine language wrote: OK Thanks Im a bit confused about oscillator range and pitch control voltage Say I have an oscillator with a frequency range of 10hz to 20khz I would have expected that inputting a 0V voltage into the VCO CV input would play a 10Hz signal from the output provided the octave dial is fully turned anti-clockwise But what would happen if I then input a -15V voltage into the CV input? The oscillator can’t play lower than 10hz, so what would happen?

In this example it would play 10hz but most oscillators have a range that exceeds the range of the tuning knob.
cptnal
 It's worth investing a few bucks in a multi meter. Endless fun watching an LFO go +5v... -5v... +5v... I think so anyway. Then plug it into Maths and watch things go really crazy.
sine language
 Hmm so the range of the oscillator may be down to 10hz but the tuning knob may only take it down to 30hz for example? If I input 0v in this case would I only get it to play 30hz? Would I need negative voltage to play lower?
sine language
 cptnal wrote: It's worth investing a few bucks in a multi meter. Endless fun watching an LFO go +5v... -5v... +5v... I think so anyway. Then plug it into Maths and watch things go really crazy.

Will definitely try this! Im one of those people that must know everything about a thing before I can be confortable with using it
Navs
 sine language wrote: OK Thanks Im a bit confused about oscillator range and pitch control voltage Say I have an oscillator with a frequency range of 10hz to 20khz I would have expected that inputting a 0V voltage into the VCO CV input would play a 10Hz signal from the output provided the octave dial is fully turned anti-clockwise But what would happen if I then input a -15V voltage into the CV input? The oscillator can’t play lower than 10hz, so what would happen?

That sounds like you've understood it: yes, the oscillator would stop, or at least stop processing/reacting to the control voltage. There is an exception - so called thru zero VCOs - that slow down to 0Hz and then reverse direction, but let's ignore them for the moment

Control voltages can be positive and negative, like an LFO. Pitch CV tends to be positive, but it depends on the range and how you scale things.

Coming back to the idea that voltages are voltages, your VCO doesn't care if you control it with a static voltage (e.g. keyboard) or a moving one (LFO or even another VCO). If it can deal with the amount (amplitude) of voltage you give it (as per your example above) it will respond the same, albeit faster or slower.
sine language
 Thank you all for your patience but I may have to rephrase my question I have a Beatstep Pro that outputs Pitch CV starting at 0V; It doesn’t output negative voltage Now I turn the fine tune knob of the oscillator completely anti-clockwise to its lowest setting and press the C0 key to output 0v on from the BSP into the 1v/octave CV input of the oscillator What frequency will I hear from the oscillator audio output?
nigel
 sine language wrote: I have a Beatstep Pro that outputs Pitch CV starting at 0V; It doesn’t output negative voltage Now I turn the fine tune knob of the oscillator completely anti-clockwise to its lowest setting and press the C0 key to output 0v on from the BSP into the 1v/octave CV input of the oscillator What frequency will I hear from the oscillator audio output?

It depends on the oscillator.

There is no generally accepted "minimum frequency" for a modular oscillator. All of the control voltages (from knobs, input CV jacks, and probably some internal adjustment) are added together, and that controls the frequency. Depending on the circuit, for some range of voltages you will get a more or less accurate one octave increase or decrease for each volt up or down. Whatever frequency you get at 0V, you should get an octave higher at 1V.

(Outside that range, the pitch will go higher or lower, but not at an exact one volt per octave. Eventually, the oscillator will go no higher or lower.)
NMNMNMNMNMN
 It really depens on the oscilator. The Mother32 (and if I'm not mistaken all Moog oscilators) track from -5V to +5V. From the Mother manual: VCO 1V/OCT INPUT This is a 1V/Octave Exponential frequency modulation input that is summed internally with the VCO FREQUENCY control, the Keyboard CV and any VCO frequency modulation. With all internal control signals at 0V, a -5 to +5V control voltage at this input will sweep the VCO frequency from 8Hz to 8kHz (10 Octaves).
Squibs
 This is really helpful for beginners, cheers James
BananaPlug
 Anyone inquisitive enough to become a newbie and ask the kind of questions asked here would do well to lookup introductory instructional material for electronics. Start by skimming through vocabulary words and getting some sense of common building blocks for circuits. You don't need to struggle through the math, just get familiar with some general concepts and building blocks. It will help you guess what's going on in your modular. Things that happen acoustically are remarkably similar to what happens in the circuits. That's why it's called ANALOG (except it might be digital - life is complicated).
dumbledog
 Just dropping in to say "sine language" is a great pun, kudos
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