Doepfer A-110-4 Thru Zero: pitch shift problem

Cwejman, Doepfer, Erica, MakeNoise, Mutable instruments, TipTop Audio, Analogue Solutions, and much more! The world’s most popular format.
Be sure to look into MANUFACTURER SUB-FORA as well..
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Doepfer A-110-4 Thru Zero: pitch shift problem

Post by windchill »

I'm still getting to grips with this module but I'm hoping someone can give me an idea what to expect regarding pitch shift.
I understand that to get TZFM the LFrq knob needs to be in the middle, and this is certainly working, but when I change the frequency of the modulator the pitch of the carrier changes too, not just the timbre. This is very pronounced if the LFM attenuator is wide open.
I'm using a second A110-4 as a modulator, sometimes direct with no intervening modules, so I don't think there's a DC offset involved.
Should the pitch of the carrier hold steady?
slow_riot
Super Deluxe Wiggler
Posts: 4002
Joined: Tue Jun 30, 2009 8:58 pm
Location: uk

Post by slow_riot »

What are you using as a modulation source? It's typical to see 500mV of offset in the modulator. This can be mostly removed through AC coupling of the linear modulation input but that doesn't always work properly, certainly not when used dynamically.

The A110-4 design is not configured especially well with regard to internal offsets, for best performance each of the 4 gain controls need to be individually trimmed but this would probably double the cost as trimming an offset from an oscillating loop is absolutely not trivial.

The LM13700 parts used vary hugely in their offset ranges, maybe you got a bad 1 or 2. The LM13700A is specced for minimum offset, although it is no longer commercially available. I can supply some although I can't guarantee you will see a marked improvement.

Offset, unfortunately is the way it goes with analogue. Digital FM if you can get around the aliasing can be modulated almost too infinity without offset problems but that level of performance is rare in analogue.

In the first instance I would look at your modulation source.

I've given Schippmann a hard time about his VCO but if he's done well in this area I might have to eat my words!
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

I'm modulating with another A110-4. I also swapped them so that I could see if they behaved the same way as carriers - and they do. So if there's a fault it's in both units.
I don't really mind because I understand that analogue fm, and thru zero especially, is going to be a compromise and something of a balancing act.
I guess I'm just trying to find out how much pitch shift to expect, if any.

It's not a static pitch-shift either - it's linked to the pitch of the modulator - to an extent I can control the pitch of the carrier by changing the pitch of the modulator, and much more than I expected.
User avatar
mbartkow
Veteran Wiggler
Posts: 741
Joined: Wed Jul 31, 2013 7:31 am
Location: Moonbase Alpha

Post by mbartkow »

I have exactly the same problem and made best efforts to ensure it is not the matter of the modulator signal having a non-zero DC, because I have a precision digital source with DC component trimmed down to a fraction of mV.

Also, I don't believe it is correct to state the linear frequency knob should be set to zero in order to get the proper FM sound (without pitch shifting). Setting it to zero means that the carier frequency becomes zero, and it's contradictory to what I know about FM synthesis. I want to get certain spectral pattern resulting from a non-zero Fc:Fm relationship. I don't want Fc=0

Also, I have noticed that the apparent pitch does not change proportionally to the amplitude of the modulator. As long as the modulation depth does not exceed the Fc, the pitch is stable. Increasing the depth suddenly makes the pitch changing, as soon as TZ point is reached. I have serious doubts if A-110-4 is indeed a TZFM oscillator. :despair:
slow_riot
Super Deluxe Wiggler
Posts: 4002
Joined: Tue Jun 30, 2009 8:58 pm
Location: uk

Post by slow_riot »

mbartkow wrote: Increasing the depth suddenly makes the pitch changing, as soon as TZ point is reached. I have serious doubts if A-110-4 is indeed a TZFM oscillator. :despair:
The A110-4 core is made up of 2 state variable oscillators that are switched between when changing polarity, each one will have an inherent and different offset, as well as different capacitor values. It's a very inefficient way to do TZFM.

(edit... that's not entirely true, it's a single SV oscillator with 2 different feedback networks that are alternated between for positive or negative output signals, as for claims about inefficiency it's likely as good as you can do in analogue)
Last edited by slow_riot on Sun Apr 16, 2017 8:28 am, edited 1 time in total.
User avatar
Risc_Terilia
Wiggling with Experience
Posts: 396
Joined: Sun Mar 20, 2016 11:50 am
Location: UK

Post by Risc_Terilia »

slow_riot wrote:
mbartkow wrote: Increasing the depth suddenly makes the pitch changing, as soon as TZ point is reached. I have serious doubts if A-110-4 is indeed a TZFM oscillator. :despair:
The A110-4 core is made up of 2 state variable oscillators that are switched between when changing polarity, each one will have an inherent and different offset, as well as different capacitor values. It's a very inefficient way to do TZFM.
Is the A110-6 the same?
User avatar
BLogic12
Super Deluxe Wiggler
Posts: 4230
Joined: Tue Jan 27, 2015 9:17 am
Location: Milwaukee WI

Post by BLogic12 »

i feel like i get the least amount of pitch shifting around -1 or +1.
try the calibration procedure very carefully. it may help.
even if there is some amount of pitch shifting, the a110-4 one of my favorite analog fm sounds.
18sekunder
Learning to Wiggle
Posts: 3
Joined: Mon Jul 11, 2016 7:02 pm

Post by 18sekunder »

If i do what you do, set LFrq in the middle, i change pitch with modulator Xtune and timbre with carrier Xtune (LFM must be turned up on carrier). I have no idea why or how this works, but it sounds pretty nice and you can play tonal stuff. Just be really carefull when you try to find he sweet spot on the carrier LFreq, it's gotta be just right, otherwise you just get noise when you turn up the carrier Xtune too much.

I would really appreciate an explanation from someone regarding this. Is it FM i'm doing? Sounds like it to me, but i'm not sure to tell you the truth.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

brandonlogic wrote:i feel like i get the least amount of pitch shifting around -1 or +1.
try the calibration procedure very carefully. it may help.
even if there is some amount of pitch shifting, the a110-4 one of my favorite analog fm sounds.
By calibration do you mean adjusting the trimming pots (which Doepfer warns is for experienced users only) or something else?
User avatar
BLogic12
Super Deluxe Wiggler
Posts: 4230
Joined: Tue Jan 27, 2015 9:17 am
Location: Milwaukee WI

Post by BLogic12 »

windchill wrote:
brandonlogic wrote:i feel like i get the least amount of pitch shifting around -1 or +1.
try the calibration procedure very carefully. it may help.
even if there is some amount of pitch shifting, the a110-4 one of my favorite analog fm sounds.
By calibration do you mean adjusting the trimming pots (which Doepfer warns is for experienced users only) or something else?
yes. dont do it if your not comfortable or fully understand the directions
.
The document A110_4_trimming_potentiometers.pdf explains the functions of the trimming potentiometers. The document is planned only for experienced users ! Please do not change the settings of the trimming potentiometers unless you are sure that you want to change certain settings. Modules which are returned with (mis-)adjusted trimming potentiometers cannot be treated as case of warranty !
also do so at your own risk
Do not change the factory adjustments unless you want to change the character of the module by intention !
Modules with modified adjustments are not taken back for money refund !
• For modules that are returned with modified adjustments during the warranty period the working time for the
re-adjustment and the shipping costs will be charged !
i do feel like my fm was a little more stable after calibration. but it took some time to do, and requires very small adjustments, careful measurements and patients.

might not be totally with it, as it only made a slight difference for me at least.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

18sekunder wrote:If i do what you do, set LFrq in the middle, i change pitch with modulator Xtune and timbre with carrier Xtune (LFM must be turned up on carrier). I have no idea why or how this works, but it sounds pretty nice and you can play tonal stuff. Just be really carefull when you try to find he sweet spot on the carrier LFreq, it's gotta be just right, otherwise you just get noise when you turn up the carrier Xtune too much.

I would really appreciate an explanation from someone regarding this. Is it FM i'm doing? Sounds like it to me, but i'm not sure to tell you the truth.
I'm getting the same behaviour when the LFreq is near the middle. The modulator freq and the LFM attenuator (or a vca on the modulator output) change the carrier pitch, but the XFM tuning on the carrier only changes the timbre. It's sort of backwards. In fact, to get a burst of stronger FM at the start, without pitch change I need to apply an envelope to the carrier XFM input instead of using a VCA on the modulator output. Odd.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

After lots of experimentation (and a conversation or two) I've worked out the issue:

Tune the carrier and modulator the same, or in a whole integer ratio, and track them together, and the tuning is stable and controllable in the expected way. The FM tones are very nice.

You can of course tune the VCOs any way you like, which will lead to some lovely, wild FM tones... just don't expect the pitch or tracking to be very easy to control.
Last edited by windchill on Sat Apr 01, 2017 11:35 am, edited 1 time in total.
User avatar
mbartkow
Veteran Wiggler
Posts: 741
Joined: Wed Jul 31, 2013 7:31 am
Location: Moonbase Alpha

Post by mbartkow »

windchill wrote: Tune the carrier and modulator the same, or in a whole integer ratio, and track them together, and the tuning is stable and controllable in the expected way. The FM tones are very nice.
The whole beauty of FM synthesis is the Fc:Fm doesn't need to be a ratio of integers, not to mention 1:1. Other implementations of TZFM do not impose such a constraint and it is never mentioned by Doepfer's docs. This would mean you can't synthesize those lovely bell sounds which require inharmonic relationships :sadbanana:
You can of course tune the VCOs any way you like, which will lead to some lovely, wild FM tones... just don't expect the pitch or tracking to be very easy to control.
Other TZFM oscillators (esp those precision digital ones) do not introduce pitch shift when the ratio is non-integer. I don't believe there should be such a limitation in 110-4, this would render the oscillator pretty useless. :waah:
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

mbartkow wrote:
windchill wrote: Tune the carrier and modulator the same, or in a whole integer ratio, and track them together, and the tuning is stable and controllable in the expected way. The FM tones are very nice.
The whole beauty of FM synthesis is the Fc:Fm doesn't need to be a ratio of integers, not to mention 1:1. Other implementations of TZFM do not impose such a constraint and it is never mentioned by Doepfer's docs. This would mean you can't synthesize those lovely bell sounds which require inharmonic relationships :sadbanana:
You can of course tune the VCOs any way you like, which will lead to some lovely, wild FM tones... just don't expect the pitch or tracking to be very easy to control.
Other TZFM oscillators (esp those precision digital ones) do not introduce pitch shift when the ratio is non-integer. I don't believe there should be such a limitation in 110-4, this would render the oscillator pretty useless. :waah:
I agree entirely. Personally I think something is up with the A-110-4 design. I'm reporting my findings and a conversation I had with the distributor, Emis. I'd really like to hear from other users of the A-110-4 because I'm confused. :despair:
User avatar
Dcramer
Super Deluxe Wiggler
Posts: 5991
Joined: Fri Mar 29, 2013 12:11 pm
Location: Canada

Post by Dcramer »

I've got one coming next week,I'll see if mine behaves the same way? :hmm:
User avatar
BLogic12
Super Deluxe Wiggler
Posts: 4230
Joined: Tue Jan 27, 2015 9:17 am
Location: Milwaukee WI

Post by BLogic12 »

I think analog through zero FM synths in modular is a tricky, touchy thing for using for very pitch sensitive uses, it requires very careful tuning.
I've even heard people having a hard time with the Rubicon, reporting similar issues. its all about finding radios that sound good, both attenuation of fm and fm frequency. There is always some amount of pitch shifting of the apparent frequency going on when you change the attenuation or the frequency, but certain ratios and settings are less apparent than others, its just about exploring. In fixed digital synths its much easier, the ratios are programmed and calibrated to work flawlessly, but that takes the fun out of it! its just not that easy in analog/modular!

check out this demo i made and read the description on the track.
some pitch shifting as the envelope closes with certain frequencies but its minimal considering im just changing the modulaion frequency to a random frequency. i think i just found the right lfm and lfrq settings for it to be a little more tolerant.
https://soundcloud.com/brandon-logic/do ... dule-demos

when i really want heavy fm sounds and accurate tracking, i use phase modulation instead (the wmd pdo). it sounds very similar to through zero modulation but it is much more stable, and its a bit easier to work with. of course i prefer the sound of analog so there's always a trade off there!

i do use the 110-4 often and dont plan on selling it ever! i love how the fm sounds but i must admit it is not my always first choice when pith is very important in a quick patch because it does require a lot of fiddling around, i use it more often for percussion/abstract sounds, although i have used it for pitch, and with careful patients of tuning and finding sweet spots it can sound great.
User avatar
nectarios
Super Deluxe Wiggler
Posts: 3020
Joined: Wed Jan 22, 2014 5:44 am

Post by nectarios »

brandonlogic wrote:I think analog through zero FM synths in modular is a tricky, touchy thing for using for very pitch sensitive uses, it requires very careful tuning.
I've even heard people having a hard time with the Rubicon, reporting similar issues. its all about finding radios that sound good, both attenuation of fm and fm frequency. There is always some amount of pitch shifting of the apparent frequency going on when you change the attenuation or the frequency, but certain ratios and settings are less apparent than others, its just about exploring. In fixed digital synths its much easier, the ratios are programmed and calibrated to work flawlessly, but that takes the fun out of it! its just not that easy in analog/modular!

check out this demo i made and read the description on the track.
some pitch shifting as the envelope closes with certain frequencies but its minimal considering im just changing the modulaion frequency to a random frequency. i think i just found the right lfm and lfrq settings for it to be a little more tolerant.
https://soundcloud.com/brandon-logic/do ... dule-demos

when i really want heavy fm sounds and accurate tracking, i use phase modulation instead (the wmd pdo). it sounds very similar to through zero modulation but it is much more stable, and its a bit easier to work with. of course i prefer the sound of analog so there's always a trade off there!

i do use the 110-4 often and dont plan on selling it ever! i love how the fm sounds but i must admit it is not my always first choice when pith is very important in a quick patch because it does require a lot of fiddling around, i use it more often for percussion/abstract sounds, although i have used it for pitch, and with careful patients of tuning and finding sweet spots it can sound great.
Awesome sound, best A-110-4 demo.
I love this VCO. There's just something about its tone, goes very well with the TWF for some wavefolding in FM patches.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

I'm certainly not going to complain about the sound. Last night, after more failed attempts to keep the pitch shift under control, I pulled the cable from the sequencer out of the 1V/oct input and was instantly rewarded with the most beautiful deep sound, which I was able to craft into a wonderful drone.
User avatar
Dcramer
Super Deluxe Wiggler
Posts: 5991
Joined: Fri Mar 29, 2013 12:11 pm
Location: Canada

Post by Dcramer »

Still awaiting mine :hyper:
User avatar
Jehos
Wiggling with Experience
Posts: 357
Joined: Tue Feb 28, 2017 8:19 am
Location: DFW, TX

Post by Jehos »

I'm really confused what you guys were expecting.

Of course you mess with the pitch of your carrier when you do FM, you're modulating its frequency. That's what FM *is*.

The pitch you perceive coming out becomes related to the harmonics at some levels of FM, not just the carrier wave. Your carrier is probably still tracking 1V/oct properly, but if the relationship between the carrier and the modulator are varying because you're not tracking the modulator at the same 1V/oct (with a buffered mult!) you're going to get different harmonics depending on what note the carrier is playing.

Run your VCO through an oscilloscope and it becomes obvious what's going on.

Digital FM seems to track better because it can force an exact relationship between the carrier and the modulator, make them both track perfectly, and even keep them in phase. All that contributes to musical-sounding FM, especially when you're getting more radical harmonics to get those bell sounds. You can do it with analog, but you have to tune very, very carefully and both your carrier and modulator need to track 1V/oct as close to perfect as possible.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

Jehos wrote:I'm really confused what you guys were expecting.

Of course you mess with the pitch of your carrier when you do FM, you're modulating its frequency. That's what FM *is*.

The pitch you perceive coming out becomes related to the harmonics at some levels of FM, not just the carrier wave. Your carrier is probably still tracking 1V/oct properly, but if the relationship between the carrier and the modulator are varying because you're not tracking the modulator at the same 1V/oct (with a buffered mult!) you're going to get different harmonics depending on what note the carrier is playing.

Run your VCO through an oscilloscope and it becomes obvious what's going on.
No, we're not talking about an effect related to our perception of harmonics. There IS a noticeable change in the fundamental. Nor is this an issue with tracking stability, it's the actual pitch-stability of the VCO when FM is applied that is under discussion. Even with analogue VCO's linear fm from a symmetric-waveform modulator with zero DC offset should not introduce a pitch change in the carrier oscillator. With analogue, it will of course to some extent, but it should not do so at a lower modulation index.
I've compared the A110-4 behaviour against a Dixie and an STO and a Disting in Thru Zero FM Vco mode and the A110-4 is most definitely way less pitch-stable under low to moderate FM.
User avatar
Jehos
Wiggling with Experience
Posts: 357
Joined: Tue Feb 28, 2017 8:19 am
Location: DFW, TX

Post by Jehos »

windchill wrote:
Jehos wrote:I'm really confused what you guys were expecting.

Of course you mess with the pitch of your carrier when you do FM, you're modulating its frequency. That's what FM *is*.

The pitch you perceive coming out becomes related to the harmonics at some levels of FM, not just the carrier wave. Your carrier is probably still tracking 1V/oct properly, but if the relationship between the carrier and the modulator are varying because you're not tracking the modulator at the same 1V/oct (with a buffered mult!) you're going to get different harmonics depending on what note the carrier is playing.

Run your VCO through an oscilloscope and it becomes obvious what's going on.
No, we're not talking about an effect related to our perception of harmonics. There IS a noticeable change in the fundamental. Nor is this an issue with tracking stability, it's the actual pitch-stability of the VCO when FM is applied that is under discussion. Even with analogue VCO's linear fm from a symmetric-waveform modulator with zero DC offset should not introduce a pitch change in the carrier oscillator. With analogue, it will of course to some extent, but it should not do so at a lower modulation index.
I've compared the A110-4 behaviour against a Dixie and an STO and a Disting in Thru Zero FM Vco mode and the A110-4 is most definitely way less pitch-stable under low to moderate FM.
How did you do a comparison with a STO and a Dixie? Those don't do TZFM.

Edit: I'm also confused because in your OP you said you're starting with the LFrq knob centered. That makes your carrier 0Hz, so everything you're hearing should come from the modulator--the A110-4 oscillator should be effectively stopped without any FM input.

Take a look here: http://electro-music.com/forum/topic-29149.html

Look at the oscilloscope picture--that's a saw wave from a Rubicon, but the concept is the same.
Last edited by Jehos on Thu Apr 06, 2017 10:01 am, edited 1 time in total.
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

Jehos wrote:
How did you do a comparison with a STO and a Dixie? Those don't do TZFM.
The STO and Dixie are indeed not capable of TZFM but they both do Linear FM.
I compared these with my A-110-4 for two reasons, firstly to check how pitch-stable analogue Linear FM can be, and secondly because my A-110-4s are not pitch-stable even when the LFrq is fully clockwise (and therefore in theory not operating in TZ mode at all).

I quite understand that analogue TZFM is probably going to be a lot less stable than standard Linear FM but I am surprised at the extent of the problem with the A-110-4.
User avatar
Jehos
Wiggling with Experience
Posts: 357
Joined: Tue Feb 28, 2017 8:19 am
Location: DFW, TX

Post by Jehos »

Right, but linear FM and TZFM are two very different beasts. You get weird lumps in your waveform when your modulator wave approaches and crosses the 0V threshold. Those make the relationship between your modulator and carrier waves matter a lot for tuning because you *are* perceiving those harmonics as pitch.

I realized one of the other things that was confusing me is you talked about doing "mild" modulation. If you're stopping your TZFM VCO by setting the LFrq to center, there's no real "mild" modulation. Attenuating the FM input just means you aren't swinging as far through the VCO's frequency range, but you're still swinging through it at audio rate (unless you're feeding it a LFO, which it sounds like you're not).
User avatar
windchill
Veteran Wiggler
Posts: 555
Joined: Thu Jan 26, 2017 6:48 am

Post by windchill »

Jehos wrote:Right, but linear FM and TZFM are two very different beasts. You get weird lumps in your waveform when your modulator wave approaches and crosses the 0V threshold. Those make the relationship between your modulator and carrier waves matter a lot for tuning because you *are* perceiving those harmonics as pitch.

I realized one of the other things that was confusing me is you talked about doing "mild" modulation. If you're stopping your TZFM VCO by setting the LFrq to center, there's no real "mild" modulation. Attenuating the FM input just means you aren't swinging as far through the VCO's frequency range, but you're still swinging through it at audio rate (unless you're feeding it a LFO, which it sounds like you're not).
Thanks for that, that's helping to clear some things up. Put simply, as I've mentioned in this thread, I'm confused. I'm, not sure what to expect from TZFM and more specifically from the A-110-4. Some veteran wigglers have said that they think the A-110-4 is not as pitch-stable as it should be. Basically, as I said earlier, I am hoping that some owners of the A-110-4 can give me an idea what to expect and how to best approach tuning stability. Clearly, I also have something to learn about TZFM. i am surprised though that the A-110-4 is still not pitch-stable even when the LFrq is fully clockwise. it doesn't help that, unusually for Doepfer, the documentation on this module is quite minimal.
Post Reply

Return to “1U & 3U Eurorack Modules”