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  #1  
Old 01-07-2020, 07:59 PM
lppier lppier is offline
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Default Why doesn’t tonedexter work on magnetic pickups?

I’m wondering what is the difference here between a piezo and magnetic such that devices like tonedexter don’t work on it?
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Old 01-07-2020, 08:46 PM
Gordon Currie Gordon Currie is offline
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James May Of Audio Sprockets posted some information about this here back in mid-2018. I wish I had a link to give you.

Essentially the gist was that there was something about the response of magnetic pickups that made it virtually impossible to know whether it would work or not. Clearly they could not ship a product that way, so they bailed on trying to also support mags.

However, a few people have gotten it to work (although many more have found it didn't work for their specific setup).

Piezos work by converting pressure/vibration into voltage. Mags work by converting movement of metal strings within a magnetic field to voltage. Something about that difference makes it difficult for ToneDexter.
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Last edited by Gordon Currie; 01-07-2020 at 08:51 PM.
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  #3  
Old 01-07-2020, 09:08 PM
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James May James May is offline
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Quote:
Originally Posted by lppier View Post
I’m wondering what is the difference here between a piezo and magnetic such that devices like tonedexter don’t work on it?
Magnetic pickups are quite non-linear transducers. To put that in laymen's terms, it means they introduce harmonic content that is not present in the motion they are sensing. Piezo transducers are, for all intents and purposes, perfectly linear representations of the motion they are sensing.

ToneDexter is designed around the concept of building a WaveMap (or impulse response). It can only do this when the pickup signal and mic signals are MOSTLY linear representations. MOSTLY is the key word, because our process still works with somewhat non-linear representations.

A number of users have gotten their magnetic pickups to give useful, pleasing results with ToneDexter. It works best if they playback with a mag pickup through a WaveMap that was created with a piezo. But, it is not as good using the piezo.

Another issue with mag pickups is that they don't give exactly the same response from moment to moment, as the string positions change slightly up and down and side to side with respect to the pole pieces. That makes it a bit of a moving target.
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Old 01-07-2020, 09:12 PM
jonfields45 jonfields45 is offline
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ToneDexter is ultimately a filter. It can only change the volume and phase of the frequency content that is in your pickup's output.

If a mic typically picks up frequency content that is totally missing from a magnetic pickup, then it can not properly train to fix that problem. It can not create something that does not exist in the pickup output, it can only make it louder or softer, and shift its phase. Some magnetic pickups might work fine. I had good results with an ES1 I tried.

Pickup systems like the Baggs Session that use distortion to make a better sounding output are also not compatible with ToneDexter. Distortion puts frequency content into the pickup output that will not be in the mic. There is no way for ToneDexter to train a fixed filter to make a distorted pickup signal sound like a mic as the distortion is a function of what note(s) you are playing, how hard you are hitting them (not linear), and will be constantly changing during training (not time invariant).
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Last edited by jonfields45; 01-07-2020 at 09:19 PM.
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Old 01-07-2020, 09:26 PM
guitaniac guitaniac is offline
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As per James May's comments, the Black Angel mag in my spruce/mahogany OM sounds very good with the WaveMap which I created using the UST in the same guitar. The Black Angel actually sounds much better with that WaveMap than with any of the guitar models in the Zoom A1 Four.
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Old 01-08-2020, 07:46 AM
varmonter varmonter is offline
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The term linear is not quite true.
sbt and ust piezos are more exponential
than mags. This response really has
nothing to do with tonedexter.
I think James May said it had to do
with the multiple string response.
where a mag has 6 pole pieces and
six independant responses. a piezo
only has one. and td likes that.
When i owned a TD. I made an Ir
with the kk in my guitar. Then played
it live using my baggs m80 mag.
This worked fine. You just cant
Create it with the mag.
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Old 01-13-2020, 02:41 PM
jonfields45 jonfields45 is offline
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In discussion with a friend we realized that as you play up the neck with a magnetic pickup, the sample point gets closer to the center of the vibrating string. That means the magnetic pickup signal will be increasingly dominated by the fundamental.

Roland's synth pickup attempts to get around this effect by placing the pickup right next to the bridge. Presumably a piezo SBT or UST is getting a consistent harmonic structure regardless of where you are fretting.

This is the essence of a system that is not time invariant or linear as the correction required to make a mag sound like a mic will depend on where on the neck you do the training and playing.

I think if you use a magnetic system for cowboy chords and only use cowboy chords for ToneDexter training, you've got a decent probability of being happy with the result.
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Last edited by jonfields45; 01-13-2020 at 05:54 PM.
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Old 01-13-2020, 07:48 PM
lppier lppier is offline
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Quote:
Originally Posted by jonfields45 View Post
In discussion with a friend we realized that as you play up the neck with a magnetic pickup, the sample point gets closer to the center of the vibrating string. That means the magnetic pickup signal will be increasingly dominated by the fundamental.

Roland's synth pickup attempts to get around this effect by placing the pickup right next to the bridge. Presumably a piezo SBT or UST is getting a consistent harmonic structure regardless of where you are fretting.

This is the essence of a system that is not time invariant or linear as the correction required to make a mag sound like a mic will depend on where on the neck you do the training and playing.

I think if you use a magnetic system for cowboy chords and only use cowboy chords for ToneDexter training, you've got a decent probability of being happy with the result.


I see .. that makes sense. I do hear the difference when playing up the neck, like what u mentioned with less overtones. Almost like the sine wave on a synthesizer.
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Old 01-13-2020, 11:36 PM
guitaniac guitaniac is offline
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Quote:
Originally Posted by jonfields45 View Post
In discussion with a friend we realized that as you play up the neck with a magnetic pickup, the sample point gets closer to the center of the vibrating string. That means the magnetic pickup signal will be increasingly dominated by the fundamental.

Roland's synth pickup attempts to get around this effect by placing the pickup right next to the bridge. Presumably a piezo SBT or UST is getting a consistent harmonic structure regardless of where you are fretting.

This is the essence of a system that is not time invariant or linear as the correction required to make a mag sound like a mic will depend on where on the neck you do the training and playing.

I think if you use a magnetic system for cowboy chords and only use cowboy chords for ToneDexter training, you've got a decent probability of being happy with the result.
Interesting. I had heard that synthesizers are triggered better by signals which are strong on fundamentals and weak on harmonics. I recall Godin making the claim that their synth-equipped Multiacs are intentionally built that way. I'm trying to get my head around how that apparent fact would relate to the placement of the Roland synth pickup.

In any event, the Baggs folks seem to be claiming that (unlike ToneDexter) their Soundscape will work with magnetic pickups. They are even using a photo of an M1-equipped guitar in their promo materials for the Soundscape. Part of the Soundscape training process is to play single pitches for the entire range of the fretboard, so that wouldn't be a case of only playing cowboy chords.

Last edited by guitaniac; 01-13-2020 at 11:44 PM.
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Old 01-13-2020, 11:48 PM
guitaniac guitaniac is offline
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Oops. Duplicate post.

Last edited by guitaniac; 01-14-2020 at 12:03 AM.
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  #11  
Old 01-14-2020, 12:05 AM
Cuki79 Cuki79 is offline
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If you are interested check out

http://www.till.com/articles/PickupResponse/index.html

http://www.till.com/articles/PickupResponseDemo/
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Old 01-14-2020, 08:15 AM
guitaniac guitaniac is offline
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Quote:
Originally Posted by Cuki79 View Post
Thanks for the links, Cuki.
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Old 01-14-2020, 08:31 AM
jonfields45 jonfields45 is offline
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Quote:
Originally Posted by guitaniac View Post
Interesting. I had heard that synthesizers are triggered better by signals which are strong on fundamentals and weak on harmonics.
The current Roland products can cover Variax like features and midi tracking.
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Last edited by jonfields45; 01-14-2020 at 08:40 AM.
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Old 01-14-2020, 08:35 AM
jonfields45 jonfields45 is offline
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Quote:
Originally Posted by guitaniac View Post
In any event, the Baggs folks seem to be claiming that (unlike ToneDexter) their Soundscape will work with magnetic pickups. They are even using a photo of an M1-equipped guitar in their promo materials for the Soundscape. Part of the Soundscape training process is to play single pitches for the entire range of the fretboard, so that wouldn't be a case of only playing cowboy chords.
Their training software might be smart enough to recognize this problem (inconsistent harmonic content up the neck) and discard data where the lowest frequency is out of the cowboy range or some other algorithmic compromise.

Maybe training your mag pup on ToneDexter with a capo at the 5th fret while playing open position chords will get you to the same place.

In my own exploration generating IRs, there is a lot to know that only trial and error can teach you. I think ToneDexter sets a very high bar for the Baggs team, in addition to a better microphone and the higher SNR it will deliver compared to a phone.

One of my first lessons in IR generation (from Cuki but not fully beaten into my head until I slammed up against it) was the various noise sources (mic, quantization real time, quantization frequency domain, window function) and how you gain them up (make them louder while not improving the signal) can ruin the IR I generate.

I am thinking the cell phone mic is not a bad choice because of its frequency response but rather its SNR.
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Last edited by jonfields45; 01-14-2020 at 08:43 AM.
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