Any way to calibrate the pitch bend wheel?

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Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

While working with my MODX today, I noticed it doing something new: it was constantly sending data to my DAW, even when nothing was happening.

Turning on my MIDI monitor, it appears that it is constantly sending pitch bend information when it is just sitting idle. It fluctuates between 54 and 58, many times a second - like jitter. Sometimes it will stop for a second or two, but then it starts right back up again.

Moving the pitch wheel has strange results as well. Moving it all the way down, the pitch bend MIDI value being transmitted goes to zero, as you would expect. However, moving it all the way up, the value only goes to 109, instead of 127.

The operation of the keyboard itself reflects this: Turning it on, so it loads the standard CFX + FM EP, the pitch wheel bends notes farther down than it does up. This is the same for every performance loaded.

I suspect something has gone wonky with the pitch wheel. Is there a calibration routine somewhere that can be run to reset the pitch wheel calibration?
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Re: Any way to calibrate the pitch bend wheel?

Unread post by parametric »

Hi ITFlyer - and welcome to the forums . . . .

That doesn't sound right. I don't own a MODX, but . . .

Is there any way you can connect by DIN midi? - and see if it's still the same?

(If you by chance have a USB Midi or Audio/Midi interface that connects to your computer?)

The DIN connectors on the MODX will be opto-isolated from any Audio/Midi Interface that connects to your computer.

I don't know how "clean" USB Midi is, in this respect. Your experience would suggest it isn't (very). :roll:

Pitchbend is SO fundamental . . . . . It should just work correctly. :naughty:

I've not heard this one on the Forum, but perhaps some other owners know different?

They'll be along in a while :wink:

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Re: Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

I don't think it has to do with the USB MIDI, for two reasons:

1. I have an optoisolator on my USB line already (USB ground loop isolator) to get rid of digital noise on the unbalanced audio out (works very well, if anyone is looking for this type of solution).

2. The pitch bend still does not register correctly even if USB MIDI is completely disconnected from the keyboard, as I mentioned - any performance selected, it bends farther down than it does up, I assume because the pitch wheel is only going up to ~109 instead of 127.

Ideally, if I could find out the sequence required to put the keyboard into service mode, I could find and run a calibration routine for the pitch wheel to see if that would fix it. For some reason, the service mode entry key sequence is a tightly-kept secret on the Internet, those who know it refuse to divulge it to others.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by parametric »

ITFlyer wrote: Fri Feb 14, 2020 3:03 pm I have an optoisolator on my USB line already (USB ground loop isolator) to get rid of digital noise on the unbalanced audio out (works very well, if anyone is looking for this type of solution).
THAT is good to know (Y)
ITFlyer wrote: Fri Feb 14, 2020 3:03 pmIdeally, if I could find out the sequence required to put the keyboard into service mode, I could find and run a calibration routine for the pitch wheel to see if that would fix it. For some reason, the service mode entry key sequence is a tightly-kept secret on the Internet, those who know it refuse to divulge it to others.
If you look here: viewtopic.php?t=12602#p75904

You could try and <PM> <Normhart> and ask if the key sequence is in the SM, and if so, what it is? :wink:

perhaps that helps?

Such strangnesses are not unknown with some Yamaha boards. IIRC, the SY85 had a quirk that no matter HOW HARD you hit the

keys - you could never get near 127 velocity . . . . (A DIY component hack eventually fixed it), although I wouldn't expect such

things of a board as new as the MODX . . . . .

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Re: Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

parametric wrote: Fri Feb 14, 2020 3:29 pm
ITFlyer wrote: Fri Feb 14, 2020 3:03 pm I have an optoisolator on my USB line already (USB ground loop isolator) to get rid of digital noise on the unbalanced audio out (works very well, if anyone is looking for this type of solution).
THAT is good to know (Y)
This is the unit I use: .....

hm, well I tried posting a link to it, but apparently this site doesn't allow it, so...

I actually have three of them, on three different synths that all have unbalanced outputs. It solved my ground loop noise in every case. My Hydrasynth (with balanced outs) doesn't have this problem. I like this solution because it fixes it on the digital side, without inserting anything into the audio chain, so the sound is not affected like it is with audio ground loop isolators.
parametric wrote: Fri Feb 14, 2020 3:29 pm If you look here: /forum/viewtopic.php?t=12602#p75904

You could try and <PM> <Normhart> and ask if the key sequence is in the SM, and if so, what it is? :wink:

perhaps that helps?
Thanks, I will do just that.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by parametric »

ITFlyer wrote: Fri Feb 14, 2020 3:39 pm hm, well I tried posting a link to it, but apparently this site doesn't allow it, so...
You CAN post the address. Just leave out the http:// bit - e.g. yamahmusicians.com

Yeah, the balanced audio thing IS annoying.

IMO, if a board is vaunted for "Pro" use, then OF COURSE it should have balanced everything . . . . . :roll:

My two Alesis Fusions' INs and OUTs are ALL balanced . . . . .

Recording Studios and Pro Concert Rigs are ALL balanced, 'cause they don't want to be chasing noise, interference and hum

problems where time is usually short . . . . :lol:

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Re: Any way to calibrate the pitch bend wheel?

Unread post by SysExJohn »

Only going from 0 to 109 is WAY out of line!

A "perfect" pitch bend wheel should go from 0 to 16,383 (or 4, I forget), mid point should be 8192 (or thereabouts), but many don't use all 14 bits allowed in the MIDI message.
The wheel in my cheapo MIDI Controller keyboard, Samson Graphite 49, puts out just 10 bit values, i.e. 0 to 1023, mid point being 512.
I would have thought the MODX would be at least that accurate.

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Re: Any way to calibrate the pitch bend wheel?

Unread post by Macke »

I have not seen any calibration instruction for this but it might be available in the service manual as has been stated before.

Othervise it might be some fault in the actual potentiometer (or whatever is) used.
SysExJohn wrote: Fri Feb 14, 2020 5:50 pm Only going from 0 to 109 is WAY out of line!

A "perfect" pitch bend wheel should go from 0 to 16,383 (or 4, I forget), mid point should be 8192 (or thereabouts), but many don't use all 14 bits allowed in the MIDI message.
The wheel in my cheapo MIDI Controller keyboard, Samson Graphite 49, puts out just 10 bit values, i.e. 0 to 1023, mid point being 512.
I would have thought the MODX would be at least that accurate.

JohnG.
I've seen threads (mainly on YamahaSynth forum) by with people complaining that the MODX pitchbend wheel only seem to have a resolution of 1-127 which of course give you noticable stepping when using it.

I believe the same thing has been noticed on Montage as well.

I'll edit and add some example threads if I'm able to find them when I'm by a computer.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

SysExJohn wrote: Fri Feb 14, 2020 5:50 pm Only going from 0 to 109 is WAY out of line!

A "perfect" pitch bend wheel should go from 0 to 16,383 (or 4, I forget), mid point should be 8192 (or thereabouts), but many don't use all 14 bits allowed in the MIDI message.
The wheel in my cheapo MIDI Controller keyboard, Samson Graphite 49, puts out just 10 bit values, i.e. 0 to 1023, mid point being 512.
I would have thought the MODX would be at least that accurate.

JohnG.
Notice the values in my screen shot - the first byte (LSB) is always zero. The second byte (MSB) is showing the pitch bend info being sent.

This tells me that the MODX is not sending LSB values, it's sending pitch bend values from 0-127 (MSB) only. Multiply this by 128 to get the actual pitch bend value. So 58 (x 128) is 7424. It's sending values of 0-16383, in jumps of 128 - so 0, 128, 256, 384, and so on.

This means the pitch bend MIDI information being sent functionally has only 7 bit resolution, not 14 bit.

Is this correct? Or is it an issue with just my MODX, which is already exhibiting problems with the pitch bend wheel? Someone else with a MODX and a MIDI monitor will have to answer that question. My guess would be that it's every MODX. I wonder if the Montage is the same?

Technically this means that the midpoint value (no pitch bend actuated) of 8192 should be sending (LSB, MSB) values of 0, 64. Mine is sending at or around 56-58, so it's low by 6-8. At full deflection my MODX is sending 109 instead of 127, which is low by 18 - close to double the offset at center pitch bend value. That's a fairly linear offset, which is what's making me think this is a calibration issue, and not a hardware issue.

Incidentally, I spoke with Yamaha today and ordered a service manual. Once I get that I'll try a recalibration of the pitch bend wheel and see if that resolves the issue.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

Macke wrote: Fri Feb 14, 2020 7:10 pm I have not seen any calibration instruction for this but it might be available in the service manual as has been stated before.

Othervise it might be some fault in the actual potentiometer (or whatever is) used.
SysExJohn wrote: Fri Feb 14, 2020 5:50 pm Only going from 0 to 109 is WAY out of line!

A "perfect" pitch bend wheel should go from 0 to 16,383 (or 4, I forget), mid point should be 8192 (or thereabouts), but many don't use all 14 bits allowed in the MIDI message.
The wheel in my cheapo MIDI Controller keyboard, Samson Graphite 49, puts out just 10 bit values, i.e. 0 to 1023, mid point being 512.
I would have thought the MODX would be at least that accurate.

JohnG.
I've seen threads (mainly on YamahaSynth forum) by with people complaining that the MODX pitchbend wheel only seem to have a resolution of 1-127 which of course give you noticable stepping when using it.

I believe the same thing has been noticed on Montage as well.

I'll edit and add some example threads if I'm able to find them when I'm by a computer.
Hi Macke,

Exactly what I just wrote in my previous post, and that jives with what I'm seeing in my MIDI monitor post. LSB is always zero, only the MSB is being changed, which means it's effectively only 7 bit resolution.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by Macke »

ITFlyer wrote: Fri Feb 14, 2020 7:16 pm
Macke wrote: Fri Feb 14, 2020 7:10 pm
I've seen threads (mainly on YamahaSynth forum) by with people complaining that the MODX pitchbend wheel only seem to have a resolution of 1-127 which of course give you noticable stepping when using it.

I believe the same thing has been noticed on Montage as well.

I'll edit and add some example threads if I'm able to find them when I'm by a computer.
Hi Macke,

Exactly what I just wrote in my previous post, and that jives with what I'm seeing in my MIDI monitor post. LSB is always zero, only the MSB is being changed, which means it's effectively only 7 bit resolution.
Yeah, I'm on mobile (slow typing) so I missed your post there.
But it seems many have made the same conclusion so you are not alone.


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Re: Any way to calibrate the pitch bend wheel?

Unread post by ITFlyer »

Before I start this post, let me qualify what I'm about to say here: I am a computer programmer by trade (for over 35 years) and I also know and have designed and built electronics for at least that long, including designing and building my own computer. So I have more than what you might consider average knowledge about this kind of stuff.

So while at work thinking about this problem today, I started thinking about what type of failure mode could cause this sort of behavior. Assuming the pitch bend wheel is a potentiometer, if one of the outside ends of the pot (the side controlling the pitch "up") had a poor connection or additional resistance of some kind, the behavior I would expect to see is exactly what I have been experiencing. The only other cause would be incorrect calibration or a hardware failure of an A/D chip somewhere. Being that the keyboard sits covered in my studio and was working fine the last time I used it, I doubt an ADC failed mysteriously while it was powered off. An analog/mechanical fault is far more likely. It could be an issue with the pot itself, or a connection.

So I decided to open it up and take a look. I discovered that yes, the pitch bend and mod wheels are in fact potentiometers.
2020-02-14 20.08.32.jpg
They both share the same positive bus feed and ground feeds, which are at either end of the resistor. Each of the wheels has a feed coming from the wiper terminal, which runs to the ADC that reads the pot value. This is important: because my mod wheel was working perfectly, that rules out the problem being resistance in either of the feed wires, because if this was the case, the mod wheel would have been affected as well.

This meant the only remaining possibilities are the pitch bend pot itself, a connector, or the ADC - and like I mentioned, I doubt it's the ADC.

I metered both pots. Both of them are identical: they are 5K linear taper pots.

I measured the pots while manipulating them. Measuring between the positive feed and the wiper, I moved the pitch bend to three positions and measured the resistance:

Pitched all the way down: 4.92 KΩ
Middle (normal position): 3.95 KΩ
Pitched all the way up: 14 Ω

Then I did the same measuring between the ground feed and the wiper:

Pitched all the way down: 8.4 Ω
Middle (normal position): 3.95 KΩ
Pitched all the way up: 4.91 KΩ

Very, very close. Close enough that it tells me that the pot is operating perfectly.

Just to be sure, I tested the mod wheel the same way and got pretty much identical results.

So not seeing any obvious smoking gun, I figured the only thing left was dirt or dust in the pot itself. I flushed both pots out with a plastic-safe no-residue contact cleaner while working the pots continually. For good measure, I also disconnected the pot/mod connector from the circuit board and cleaned it as well.

I then put the keyboard back together, plugged it all in, and the verdict: it's fixed!!! No more spurious pitch bend MIDI jitter, and the pitch bend range has been restored.

For those who might be curious, I'll post some pictures of the guts of the keyboard that I took while it was open.
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Re: Any way to calibrate the pitch bend wheel?

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Re: Any way to calibrate the pitch bend wheel?

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Re: Any way to calibrate the pitch bend wheel?

Unread post by YamahaUser »

ITFlyer wrote: Sat Feb 15, 2020 3:02 am[...]
They both share the same positive bus feed and ground feeds, which are at either end of the resistor. Each of the wheels has a feed coming from the wiper terminal, which runs to the ADC that reads the pot value. This is important: because my mod wheel was working perfectly, that rules out the problem being resistance in either of the feed wires, because if this was the case, the mod wheel would have been affected as well.

This meant the only remaining possibilities are the pitch bend pot itself, a connector, or the ADC - and like I mentioned, I doubt it's the ADC.

I metered both pots. Both of them are identical: they are 5K linear taper pots.

I measured the pots while manipulating them. Measuring between the positive feed and the wiper, I moved the pitch bend to three positions and measured the resistance:

Pitched all the way down: 4.92 KΩ
Middle (normal position): 3.95 KΩ
Pitched all the way up: 14 Ω

Then I did the same measuring between the ground feed and the wiper:

Pitched all the way down: 8.4 Ω
Middle (normal position): 3.95 KΩ
Pitched all the way up: 4.91 KΩ

Very, very close. Close enough that it tells me that the pot is operating perfectly.

Just to be sure, I tested the mod wheel the same way and got pretty much identical results.
[...]
Sorry, but not quite. What you've really got is a pair of nominally 10 KΩ pots with the end terminals wired in parallel. The giveaway is the 3.95 KΩ reading at center. An isolated 5 KΩ linear taper pot would measure about 2.5 KΩ at center, and when paralleled with another measure even lower.

I don't have the time to get my CAD program up, so a description will have to do. Let's presume the pots are ideal, so exactly 10 KΩ. When measuring from one end to the wiper with the pot centered, you're actually measuring half of that pot's resistance (5 KΩ) in parallel with the series connection of the other half plus that of the entire resistance of the other pot (10 KΩ). In other words, 5 KΩ in parallel with 15 KΩ. That calculates to 3.75 KΩ, close enough to the 3.95 KΩ you measured with the real pots.

I flushed both pots out with a plastic-safe no-residue contact cleaner while working the pots continually.
Most pots are manufactured with a small amount of lubricant on the resistance track. If that's removed with a "no-residue" contact cleaner, the pot's lifespan can be reduced. You might want to use a control cleaner that includes a small amount of lubricant.
Last edited by YamahaUser on Sat Feb 15, 2020 4:18 am, edited 1 time in total.


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