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Tuning aid for a VCO
MUFF WIGGLER Forum Index -> Modular Synth General Discussion Goto page 1, 2  Next [all]
Author Tuning aid for a VCO
mskala
I use Tiptop Z3000 VCOs and often tune them to match my MIDI interface by playing an A above middle C through the MIDI, then tuning the VCO to bring its output shown by the built-in frequency counter to 440Hz. Occasionally I tune them to some other frequency, but it's usually some exact musical interval off from there, such as a fifth or some number of octaves. Easy to calculate the target frequency reading.

However, lots of other ways of tuning VCOs are possible. Some people go strictly by ear to whatever sounds good and don't care about matching the tuning of other instruments. Some people use different kinds of external tuning devices, for oscillators that don't have built-in frequency counters.

In principle, it's possible to imagine a VCO with a permanent tuning - 0V always some specific frequency, possibly shifted by an octave switch, without needing manual tuning to hit that frequency. There might or might not also be a knob for detuning it with a way of removing that effect (detent in the middle, turn it fully one way or the other, precise graduations on the knob/panel, etc.) when exact tuning is desired.

I did a trade show demo recently where it seemed like every third visitor to my table went straight for the "coarse tuning" knob and shifted my demo out of key. Then after they left I'd have to go disconnect the FM, stop the sequencer, go play an A, and retune the oscillator so the demo would sound right for the next visitor. I ended up feeling that there had to be a better way. Part of the solution that particular day turned out to be carefully tangling the cables over the oscillator to make the tuning knobs less visible, but that's another story.

What I'd be interested to know is, what do people prefer? I'm playing with a VCO design of my own, and at least for my own use, some easier way to keep the MIDI interface and the VCO in line with each other would be nice. The "fixed tuning, no adjustment needed" approach is what I'd probably find most convenient for myself. Basically, just have a trimmer on the board instead of or in addition to the front-panel tuning control. Set that and leave it. But it's not easy to get permanent tuning right in an analog oscillator because it means the thermal compensation has to be really good - thermal compensation is needed for offset, not just for tracking. I'm not sure I've ever seen a precisely-specified 0V frequency in an analog modular oscillator for that reason. It's more typical of digital oscillators. And even if fixed tuning worked perfectly, not all users would want the same 0V frequency, and even one user wouldn't want the same 0V frequency all the time.

I like having a digital frequency counter on the Z3000, but I know not everybody does. Tuning that way is very flexible - many different tuning targets possible - but it still requires a manual adjustment to get the counter to the desired reading. I've also thought about other kinds of tuning aids that might have a less obtrusive display - something like a guitar tuner's up/down indications built into the VCO.

Another idea might be to have a more active tuning device built in: tune near the desired note, press a button, and then a microcontroller detects the current frequency, identifies the nearest standard note, and creates an offset voltage to push the oscillator onto the note exactly; that offset is then held until next time the button is pressed. Very flexible for different notes, less manual tweaking needed, and when that feature isn't desired, one just doesn't press the button. There'd still be front-panel tuning controls that the user could adjust for free analog tuning when desired.

What do others think - how do you tune your VCOs, how do you want to tune your VCOs, and how important is it or isn't it?
Phil999
in the 90's I used a simple tuning fork. Not really because I wanted to be accurate, it was because I have 4 VCO's in the Formant modular system that I often used simultaneously, so I had to tune and re-scale them occasionally, especially when I moved my studio to a different place.

Today I don't do that anymore because I use the Formant VCO's in a different way (FM, AM, ringmod), and newer VCO's (Mannequins Mangrove, Endorphines Furtherrr) as main voices. What is important to me now are the intervals. With the help of the Tubbutec uTune module this has finally become possible in an easy way.
flo
I tune by turning the octave / coarse / fine tune controls until I reach the desired frequency hihi If help is needed, I use the Ableton tuner or a guitar tuner. I don't see an issue there? Maybe put a sticker saying "Please don't change the tuning!" or so on the coarse knob for demos. A locking poti could be nice if you design something yourself.

I don't think having a fixed frequency would be a particularly good idea for a main VCO, you want to be able to adjust it without using CV. A good VCO really needs trimmers on the rear anyways to calibrate the scaling and adjust the front panel controls. My favorite VCO design is with octave switches and a fine tune, ideally with a switchable range. I do have some without octave switches though and I highly recommend the Hinton PitchMaster (if your case is deep enough), it's amazing for tuning and all sorts of mixing and offset applications: http://hinton-instruments.co.uk/paprod/modular/pitchmaster/index.htm



Cheers Guinness ftw!
Dave Peck
I have to disagree with your phrasing here:

" Some people go strictly by ear to whatever sounds good and don't care about matching the tuning of other instruments. "

I tune by ear, and I do care about matching the tuning of other instruments. For me, it's actually easier to set the correct tuning by ear than any other way. Either an exact tuning match, or detuned from the reference osc with a specific 'beat frequency', or set to a specific interval like a perfect fifth.

I do the same a couple of times a year when I'm re-calibrating the 1V/OCT tracking on all of the oscs in the modular (eight of them). For me it's easier to do it by ear than watching a visual meter.

Also, you mentioned 'imagining a VCO with permanent tuning' and there have been such tuning reference oscs for quite a while. For example, the minimoog included an A-440 reference osc specifically for tuning purposes.
Parnelli
I had once thought about a tuner. perhaps a Peterson Strobe, but this instrument is different than any other that I've played in the past.

I tune by ear because I like my oscillators to be a few cents off from each other, especially if they're set to similar waveforms. This tends to give me an undulating wave with both frequencies beating against one another.

When I get a guitar I will tune the guitar and then tune the synth to the guitar by ear, provided I can still hear as well as I do.
Blairio
flo wrote:

...... A good VCO really needs trimmers on the rear anyways to calibrate the scaling and adjust the front panel controls.


I suggest a good VCO needs trimmers (or at least the octave scaling trimmer) accessible through the front panel. The reason is that analog VCO's are temperature sensitive, even ones with temp compensation. From the time you take an oscillator module out of its rack to tweak a trim pot on the PCB, you start to get a temperature reduction on the module itself, compared to the operating temperature within the rack enclosure.

Some VCO makers recognise this. My MakeNoise STO and SSF Spectrum both present the octave scaling trimmer through a small whole in the front panel, so you don't have to remove the module when adjusting its octave scaling.
Blairio
Dave Peck wrote:
I have to disagree with your phrasing here:

" Some people go strictly by ear to whatever sounds good and don't care about matching the tuning of other instruments. "

I tune by ear, and I do care about matching the tuning of other instruments. For me, it's actually easier to set the correct tuning by ear than any other way. Either an exact tuning match, or detuned from the reference osc with a specific 'beat frequency', or set to a specific interval like a perfect fifth.

I do the same a couple of times a year when I'm re-calibrating the 1V/OCT tracking on all of the oscs in the modular (eight of them). For me it's easier to do it by ear than watching a visual meter.

Also, you mentioned 'imagining a VCO with permanent tuning' and there have been such tuning reference oscs for quite a while. For example, the minimoog included an A-440 reference osc specifically for tuning purposes.


Perhaps ' permanent tuning' refers to an oscillator that doesn't need tuning (or self tunes), rather than one which does need tuning but also has a 440hz reference tone available onboard? I guess most DCO's have this capability, but I am not aware of many Eurorack DCO's (as opposed to straight digital oscillators). When it comes to modular synth oscillators, I reckon a middle C reference tone might be more useful than concert A, since most oscillators follow the 1volt/oct standard.
trentpmcd
Dave Peck wrote:
I have to disagree with your phrasing here:

" Some people go strictly by ear to whatever sounds good and don't care about matching the tuning of other instruments. "

I tune by ear, and I do care about matching the tuning of other instruments. For me, it's actually easier to set the correct tuning by ear than any other way. Either an exact tuning match, or detuned from the reference osc with a specific 'beat frequency', or set to a specific interval like a perfect fifth.

I do the same a couple of times a year when I'm re-calibrating the 1V/OCT tracking on all of the oscs in the modular (eight of them). For me it's easier to do it by ear than watching a visual meter.

Also, you mentioned 'imagining a VCO with permanent tuning' and there have been such tuning reference oscs for quite a while. For example, the minimoog included an A-440 reference osc specifically for tuning purposes.


I'm pretty much the same - it is easier for me to tune by ear. I used to use my digital piano, since it is hard to change pitch, but I found I was guesstimating at times. I now use the A-440 output on my Boog (cool they kept it this feature from the original). I can easily hear the beating for any oscillator that I want to tune. I can also very easily tune to whatever I want, super simple.
mskala
Blairio wrote:
Perhaps ' permanent tuning' refers to an oscillator that doesn't need tuning (or self tunes), rather than one which does need tuning but also has a 440hz reference tone available onboard?


When I wrote "permanent tuning" I meant that the frequency when the control voltage input is 0v, is permanently fixed, or at least there is a selectable mode where that is the case even if the oscillator can also operate in other modes. So that 2.75V is always 440Hz, or whatever, and you don't have to do something manual on a regular basis to tune the oscillator to match your CV generator. The tuning in such a case is permanent.

Including a reference oscillator, or some other aid to manual tuning (like the Z3000's frequency counter) is different from that because it still requires the user to tune the oscillator manually. Having some kind of feature that automatically tunes the oscillator, but still requiring the feature to be manually invoked periodically, is yet a third way to do things.

Blairio wrote:
When it comes to modular synth oscillators, I reckon a middle C reference tone might be more useful than concert A, since most oscillators follow the 1volt/oct standard.


I don't get what "the 1volt/oct standard" has to do with C being a more useful reference tone than A. Volt/octave specifies the scale of the voltages, not the frequency at 0V which is the subject here. Using A has the big advantage that it's an integer frequency in Hz.

Is your idea that 0V = C would be a preferred tuning to use, in which case the oscillator could be adjusted with no control voltage plugged into it? That makes some sense, but then it probably wouldn't be middle C but some lower C that would be preferable for the 0V frequency. Many things that generate control voltages are unable to generate negative ones, so you'd usually want 0V to be lower than the lowest notes you want to play.
Blairio
mskala wrote:
Blairio wrote:
Perhaps ' permanent tuning' refers to an oscillator that doesn't need tuning (or self tunes), rather than one which does need tuning but also has a 440hz reference tone available onboard?


When I wrote "permanent tuning" I meant that the frequency when the control voltage input is 0v, is permanently fixed, or at least there is a selectable mode where that is the case even if the oscillator can also operate in other modes. So that 2.75V is always 440Hz, or whatever, and you don't have to do something manual on a regular basis to tune the oscillator to match your CV generator. The tuning in such a case is permanent.


I take your point.

mskala wrote:

I don't get what "the 1volt/oct standard" has to do with C being a more useful reference tone than A. Volt/octave specifies the scale of the voltages, not the frequency at 0V which is the subject here. Using A has the big advantage that it's an integer frequency in Hz.


The reason I personally find C more useful than A for calibrating (not tuning) VCO's is because the standard octave scaling method involves moving between C2 and C4 (multiples of 1 volt) until you have achieved the best available accuracy at both points. I have an oscilloscope which puts out pretty precise multiples of 1 volt, so working in his way serves me well. In hindsight A2 and A4 would service just as well if you have accurate A2 and A4 reference tones, but I guess you stick with what you know.

Some VCO have better tracking than others. My two Doepfer A-110's track well over 6 1/2 octaves. My Bubblesound VCOb manages close to 7 octaves. My MakeNoise STO gets a bit wayward after 4 octaves.
flo
Blairio wrote:
flo wrote:

...... A good VCO really needs trimmers on the rear anyways to calibrate the scaling and adjust the front panel controls.


I suggest a good VCO needs trimmers (or at least the octave scaling trimmer) accessible through the front panel.


Sure, why not.

Blairio wrote:
The reason is that analog VCO's are temperature sensitive, even ones with temp compensation. From the time you take an oscillator module out of its rack to tweak a trim pot on the PCB, you start to get a temperature reduction on the module itself, compared to the operating temperature within the rack enclosure.


If your VCO drifts because you take it out of the case, it's either not a very good VCO or you seriously need to vent your case, or both thumbs up

Blairio wrote:
Some VCO makers recognise this. My MakeNoise STO and SSF Spectrum both present the octave scaling trimmer through a small whole in the front panel, so you don't have to remove the module when adjusting its octave scaling.


Interesting, I never noticed that on them. But that single trimmer is hardly enough to properly calibrate a VCO, are there further ones on the rear? If so, doesn't that mean that you need to take them out of the rack anyways for a proper calibration?

mskala wrote:
When I wrote "permanent tuning" I meant that the frequency when the control voltage input is 0v, is permanently fixed, or at least there is a selectable mode where that is the case even if the oscillator can also operate in other modes. So that 2.75V is always 440Hz, or whatever, and you don't have to do something manual on a regular basis to tune the oscillator to match your CV generator. The tuning in such a case is permanent.


And I think that wouldn't be very useful. There's a lot of reasons why you'd want to adjust the tuning. For example, I think tuning the VCOs to the root of your key is often sensible - e.g., if you don't want to change the scale on a quantizer or sequencer or if you want to "mute" the pitch CV and have just the root playing. So, IMO 0V should be the lowest octave of the root that you're going to use in most cases, not some fixed arbitrary frequency that you can only change via CV.

You did bring a fixed frequency oscillator to the market already... I don't want to be rude, but you seem a bit obsessed with the idea.

Cheers Guinness ftw!
Blairio
flo wrote:


Blairio wrote:
The reason is that analog VCO's are temperature sensitive, even ones with temp compensation. From the time you take an oscillator module out of its rack to tweak a trim pot on the PCB, you start to get a temperature reduction on the module itself, compared to the operating temperature within the rack enclosure.


If your VCO drifts because you take it out of the case, it's either not a very good VCO or you seriously need to vent your case, or both thumbs up


Its not the particular analog VCO, It is in the nature of analog VCO's. This is nothing new.

flo wrote:


Blairio wrote:
Some VCO makers recognise this. My MakeNoise STO and SSF Spectrum both present the octave scaling trimmer through a small whole in the front panel, so you don't have to remove the module when adjusting its octave scaling.


Interesting, I never noticed that on them. But that single trimmer is hardly enough to properly calibrate a VCO, are there further ones on the rear? If so, doesn't that mean that you need to take them out of the rack anyways for a proper calibration?
Cheers Guinness ftw!


There are generally 2 parameters which the average user may need to tweak ( I am excluding wave shapes here). One is Fine Tune, and the other is Octave Scaling. Pretty much every VCO has a fine tune control on the front panel. This leaves the octave quantising trimmer. With a VCO like the Spectrum or STO you don't need to take them out the rack to do the needful.
Synthbuilder
Blairio wrote:
I suggest a good VCO needs trimmers (or at least the octave scaling trimmer) accessible through the front panel.

The problem is that by making them accessible then users will feel the need to adjust them. While this does sound a good idea, there are a few things to bear in mind.

From my many years as a repair technician I can't remember just how many busted front panel trimmers I have seen because there are so many. Users would use inappropriate tools to adjust them, would apply too much force, or use them too often.

Secondly, most trimmers, even the expensive ones, are not designed to be moved that often. 200 adjustments is about the maximum, and while this may seem to be a lot, musicians do love a good fiddle in their search for ultimate tone, so you often end up with worn out trimmers.

Thirdly, you may be surprised just how many trimmer adjustments are carried out by users that make things worse.

Tony
flo
Blairio wrote:
flo wrote:


Blairio wrote:
The reason is that analog VCO's are temperature sensitive, even ones with temp compensation. From the time you take an oscillator module out of its rack to tweak a trim pot on the PCB, you start to get a temperature reduction on the module itself, compared to the operating temperature within the rack enclosure.


If your VCO drifts because you take it out of the case, it's either not a very good VCO or you seriously need to vent your case, or both thumbs up


Its not the particular analog VCO, It is in the nature of analog VCO's. This is nothing new.


Clearly there are differences between designs and makes with regard to temperature sensitivity. What I am suggesting is that a VCO that is so sensible to it isn't very good, or that you need some ventilation if there's such a large difference in temperature between your room and the inside of your case.

Blairio wrote:
There are generally 2 parameters which the average user may need to tweak ( I am excluding wave shapes here). One is Fine Tune, and the other is Octave Scaling. Pretty much every VCO has a fine tune control on the front panel. This leaves the octave quantising trimmer. With a VCO like the Spectrum or STO you don't need to take them out the rack to do the needful.


There's often a "high range tracking" trimmer as well, which is for the higher octaves as the name suggests. A "frequency" trimmer is needed to offset your front panel controls (you set the front panel controls how you want them and use the "frequency" trimmer to get the frequency you want with those front panel settings - after you've carefully calibrated the scaling).

Tony makes a good point, too. Just recently I've seen a Cwejman S1 with two broken rear trimmers. Looked like somebody was using way too much force and tried to turn them further than they would go.

Cheers Guinness ftw!
hamildad
M Geddes Gengras has 4x STO's with the main tuning knobs removed to keep everything in 'tune' or at least with the same pitch reference to 0V.

https://www.factmag.com/2015/10/09/against-the-clock-m-geddes-gengras/
mskala
Synthbuilder wrote:
The problem is that by making them accessible then users will feel the need to adjust them.


Indeed. And an adjustment that really shouldn't be changed is positively magnetic to users; it will be the first thing they try to change any time they try to "fix" a device that isn't broken.

Ultimately, the owner of the module gets to do whatever they want with with their property, and if they want to mess with the V/oct scaling until they wear out the trimmer, that's their business. The situation is also a little different with a DIY module where the builder does genuinely need to adjust the scaling once at build time. But I think informed users will not really want to change V/oct scaling very often. I also think that if a VCO is so temperature-sensitive that it needs frequent adjustments of the V/oct scaling due to temperature sensitivity, there is something really wrong. The more likely reason a properly temperature-compensated VCO might seem to need frequent changes to V/oct scaling would be to compensate for differences between different CV sources, which can have varying inaccuracies of their own - and that gets back to my original question about tuning to match a CV source.

The frequency of a VCO with an exponential control voltage (V/oct or 1.2V/oct or similar - not Hz/volt) is given by exp(ax+b) where x is the control voltage, a represents the V/oct scaling, and b represents the tuning. Standard practice is that a is set only by a trimmer and doesn't change in normal operation, while b is adjusted from the front panel and needs to be adjusted frequently. My own experience is that I usually use one specific value for b - the unique value needed to match my MIDI interface. The tuning knobs exist for a reason and yes, I sometimes want to tune my oscillators differently. But usually not. It would be nice if the tuning process, by which I mean adjusting b to the one value that I want most of the time, could be less of a chore. Finding the sweet spot could be easier and faster given that it's in the same place every time.

However, it's sounding to me like I have an answer to my question: other modular users posting here do not actually want a built-in VCO feature aimed at this use case after all. That's useful information.
flo
mskala wrote:
The more likely reason a properly temperature-compensated VCO might seem to need frequent changes to V/oct scaling would be to compensate for differences between different CV sources, which can have varying inaccuracies of their own - and that gets back to my original question about tuning to match a CV source.


CV sources should have trimmers as well to calibrate their scaling if they are off. If they don't, Hinton again has you covered with the Trimmer: http://www.hinton-instruments.co.uk/paprod/modular/trimmer/index.htm. You should only need to re-calibrate the VCOs if you change your system (i.e., if you exchange modules)...
Blairio
mskala wrote:

However, it's sounding to me like I have an answer to my question: other modular users posting here do not actually want a built-in VCO feature aimed at this use case after all. That's useful information.


I recently put a bunch of modules which reflected the functionality of an ARP Odyssey into a 3U 84HP case. I used MI Yarns to replicate the Odyssey's Duophony. Another Odyssey capability is to disable one VCO from keyboard tracking - in effect pedalling a single note.

Perhaps that constitutes a use case for your fixed frequency VCO?
mskala
Blairio wrote:
Perhaps that constitutes a use case for your fixed frequency VCO?


Not "my" fixed-frequency VCO. Fixed-frequency was flo's idea.

I'm interested in having a readily-accessible fixed tuning, that is, making it as easy as possible for the keys on the keyboard to play their standard concert-pitch frequencies when that is desired. Or, even, just a tuning aid making it as easy as possible to adjust the manual tuning knobs to that target.

We don't expect to routinely use tracking settings other that 1V/oct (or 1.2V/oct, etc., as appropriate to the format) - even those who want tracking to be trimmable from the front panel want that so as to be able to keep it on the standard setting in the face of temperature and other changes, not because they often want to switch between 1V/oct, 0.63V/oct, and 2.9V/oct. Someone who does want other scaling would usually use an exponential FM input instead of the one called "V/oct." We do often want the frequency at 0V to be different values... but I, at least, have one value of the 0V frequency that I most often want to use, more often than any others, and would value a feature for making it easy to hit that value consistently.

It surprises me that many people writing here who want V/oct to be consistent don't want the frequency at 0V to be consistent too - not even as a selectable mode that doesn't have to be active all the time - but that's why I asked.
flo
mskala wrote:
Blairio wrote:
Perhaps that constitutes a use case for your fixed frequency VCO?


Not "my" fixed-frequency VCO. Fixed-frequency was flo's idea.


Haha, my wording maybe (probably framed by the description of your fixed frequency LFO), but neither my idea nor my desire. I can think of hundreds of use cases for oscillators that you don't need to VC or even adjust - but I prefer having the option and not using it rather than not having the option. Especially in something as crucial as VCOs.

mskala wrote:
It surprises me that many people writing here who want V/oct to be consistent don't want the frequency at 0V to be consistent too - not even as a selectable mode that doesn't have to be active all the time - but that's why I asked.


Because the scale of V/Oct is absolute and needs to be precise and consistent (like the distance between guitar frets, for example). The 0V point in that scale is relative and there should be a way to adjust it (like a guitar capo).
mskala
flo wrote:
Because the scale of V/Oct is absolute and needs to be precise and consistent (like the distance between guitar frets, for example). The 0V point in that scale is relative and there should be a way to adjust it (like a guitar capo).


I think we are not really so far apart. I want there to be a way to adjust it, too, but I want it to be easy to adjust it to a specific reproducible target when desired.
flo
mskala wrote:
I think we are not really so far apart.


thumbs up

mskala wrote:
I want there to be a way to adjust it, too, but I want it to be easy to adjust it to a specific reproducible target when desired.


How long does it take you to repitch a Z3000 to A 440Hz or whatever you want? I find it easy enough to do that using the front panel controls on my VCOs.

Apart from that, I think a locking poti would be nice, if you can find a good one - as suggested further above. But that's also not exactly what you are describing, for any "auto-tuning" polysynth-style the respective front panel controls would need to be digitally controlled internally with VCAs everywhere, as far as I can see (I am of course assuming we are talking about analogue VCOs here). Besides the technical can of worms that opens, you get into UI issues such as controls not corresponding to the actual setting anymore (no "what you see is what you get"), like pretty much any programmable synth. Also, it really would need to be a preset system where you can set what that "reproducible target" should be as well. Next, you surely want to be able to have presets for the whole module, not just the frequency... And then a way to step through them with CV and triggers. Something like that would allow a lot of cool things, but it gets complicated quickly and I suppose it would be rather tricky to implement properly.

Another idea would be some sort of external (i.e., not integrated into the VCO) Expert Sleepers style "calibration" (but only for the tuning) module where you can set a desired target frequency and the module would listen to the VCO and at the same time spit out CV offsets to adjust it to the target.
Pelsea
If I had my druthers, turning the coarse and fine controls all the way left would put 0v on the pitch bus, and the oscillator would run at 16.35 Hz. This would simplify calibration and make the oscillator easy to use with MIDI convertors.

Since that's not the case, I routinely use a Korg tuner, which provides a pitch reference and displays tuning in cents.
cycad73
I would like a trimpot for making very precise tracking adjustments, so I can keep two oscillators in precise tuning (say with octave relationships) with zero audible beating over a 6-7 octave range. This is what is possible with the ARP 2600 (there’s a trimpot accessible on the panel, normally covered with a black plastic cap) and unfortunately nowhere else. Precise tuning here means probably less than 0.2 Hz, so there’s not even a perceptible animation in the sound, it’s like a suboscillator.

Usually, there’s hard or soft sync for this application, but it doesn’t have the same sound. Even soft sync with an octave relationship will add a certain buzz.

There’s also the corollary of exponential FM without any beating or change in timbre, also without resorting to sync. This I can do with a bit more difficulty on the 2600, but I’ve found it impossible elsewhere, where I have to resort to some kind of sync.
Phil999
as the title of the thread says tuning aid for VCO's, it might be worth mentioning the Endorphines Terminal extender module named 'gateway', and the 'autopilot' module.

http://endorphin.es/endorphin.es--modules.html
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