least magnetic distortion?

[David Schwab]

David S you'll agree that an active sustainer can be phase flipped to become a string mute. So why not a passive mute effect? Granted most pickups will have less than 10k ohm of loading but I'm betting that at certain frequencies where cable capacitance is part of a tuned LRC circuit we could expect to see noticeable string damping. Again probably easier to check for than to try to calculate.

Oh it can, like with the Moog guitar. But the key word is active. If you had enough juice to do that with a passive pickup, then you should be able to run the bridge pickup into the neck pickup and get sustain, right?

It is easy to check. I have basses with no pickups in them I use for pickup testing. They don't sustain any more than when there is a pickup, and when that pickup is plugged into a load. If that were the case every guitar would be active by now because that would be a big problem!

I just think the amount of current running though the pickup isn't enough to change the permanent magnet's field enough to effect the strings.

[Joe Gwinn]

The output of a guitar pickup is a very small amount of power. It does not move the magnetic material along the B H curve very much, as happens in a motor or a speaker. I suspect that for a pickup there is no significant distortion generated this way.

Correct. There was a loud debate on this a few years ago (before you first posted, I think), and I made some tests, driving pickups so hard that they had 70 volts rms at the output. There was no significant harmonic distortion due to the magnetic materials. The results are posted in either the current forum, or in the predecessor AMPGE forum.

[uvacom]

Could we also assume that the magnetic window is only the width of a keeper or magnet, i.e. ignore the effects due to sampling window width?

Uvacom said:

"The magnetic field does introduce some distortion, since the mag field decreases with distance from the polepieces. That means that any movement of the string in the "Y" direction is not detected equally, so there will be some second-order harmonic distortion from the pickup itself."


I wonder about this. It seems to me that the lack of signal due to movement in directions that are not sensitive is not a distortion of the wave form, but the nature of sound percieved by a single sensor, like an eardrum. When we hear the string in the air we experience the same sort of effect of the vibration of the string moving toward us (normal to the ear drum) smothly varying to perpendicular and back, which evolves during the attack. In the air we hear that as a change of loudness, i.e. the same fundamental sine wave, but less excursion, not as the addition of the upper harmonics of second order distortion, which an asymetric wave form produces.

I'm trying to differentiate between the change in amplitude due to orientation and the 2nd order generated when the string moves through regions of different field strength or field orientation DURING ITS EXCURSION and the top and bottom of the wave vary in amplitude.

There is a distinct difference between a string vibrating in a magnet field, and a string's acoustic vibration as we sense it in our ears. For our ears, when the string is moving forward, it compresses the air above the local atmospheric pressure, ultimately pushing our eardrum inward from its resting state. But when it is traveling away from our ear it decompresses the air below atmospheric pressure, which pulls our eardrum outward from its resting state. Both of these happen equally.

But when the string is vibrating in the magnetic field, it is not a uniform field so when the string moves toward the pickup the current travels in one direction, and when it moves away, it travels in the opposite direction but since the field is weaker, the negative alternation of the string's cycle is not picked up as strongly. To our ears, it is. But not to the pickup.

[uvacom]

Correct. There was a loud debate on this a few years ago (before you first posted, I think), and I made some tests, driving pickups so hard that they had 70 volts rms at the output. There was no significant harmonic distortion due to the magnetic materials. The results are posted in either the current forum, or in the predecessor AMPGE forum.

Well there you go then. It was an interesting hypothesis anyway!

[Possum]

...

I was going to add that point, magnets don't distort audio signals, there isn't distortion coming from pickups. Pickups are just microphones with a limited frequency response. The distortion comes from the amps only. Darker pickups with powerful magnets or high windings push the preamp section of the amp so the distortion happens there or by the preamp pushing the power section into distortion, usually when the amp is turned way up. Vintage amps naturally distort when turned up, well at least the good ones do :-) Lower power pickups like some vintage strat pickups have low output and a higher frequency response than humbuckers so they don't make the amp work very hard so less distortion..

[JGundry]

I think there is a sort of magnet distortion that goes on with magnets like A2 and unoriented A5 that have a low coercive force. These magnet have a sort of trailing crunch from pick attack that you don't get as much of with a higher coercive force magnet like oriented A5.

Whether this is really magnet distortion I doubt. My completely non scientific take on it is that low coercive force magnets allow the string to vibrate more freely after the note is plucked. The lower coercive force allows just a bit more of the very short duration, percussive, string against fret rattle than you would get from a higher coercive force magnet like oriented A5. That very brief extended rattle we perceive as crunch. Not really magnet distortion but it is more or less due to the magnet.

I could be totally full of it with this explanation though.

[Possum]

...

I wouldn't call it distortion, in amps its called "sag" and is very desirable for blues.

[Steve Conner]

But when the string is vibrating in the magnetic field, it is not a uniform field so when the string moves toward the pickup the current travels in one direction, and when it moves away, it travels in the opposite direction but since the field is weaker, the negative alternation of the string's cycle is not picked up as strongly. To our ears, it is. But not to the pickup.

This is true. You can do the math and show that harmonics are generated by the non-uniform field. In general, for a string vibrating in both horizontal and vertical directions, they tend to distort the wave from a sine towards a sawtooth.

This is not distortion due to the magnetic materials, it's purely due to the geometry of things. (The vibrating arc of the string is not negligible compared to the distance from string to pickup.)

Since the string already has overtones of its own, it's a moot point whether it makes any noticeable difference.

[JGundry]

I wouldn't call it distortion, in amps its called "sag" and is very desirable for blues.

Not talking about sag. Well aware of sag.

[Possum]

...

I think you're getting into quantum physics. "Trailing crunch" sounds like breakfast cereal, I'm not even sure I understand what you mean there....

[JGundry]

I think you're getting into quantum physics. "Trailing crunch" sounds like breakfast cereal, I'm not even sure I understand what you mean there....

I'm pretty sure you have heard this and it is just a matter of putting it in words. A2 and unoriented A5 have a crunchy quality when a note is picked. Substitute a crunch that decays quickly after the note is picked for trailing crunch. Oriented A5 has a more focused tone when you pick the note, less of this crunch. We are talking about same pickup, same amp, just different magnets.

[Possum]

...

The only thing I've experienced like that and maybe its the same thing, is what I call "grainy" tone, and have only heard it in real PAFs and in some of my work with those. I hear it mostly in A5 magnets, with 11 gauge strings, the right combo of cherry picked steels, and its most noticeable in string bends on the unwound G string. That "Push Push" by Herbie Mann and Allman is a good example of that. I do hear some of it in bright alnico 2 I have also. Its the brighter magnets that bring it out. And only in vintage tube amps with larger power tubes like my Vibrolux and 6L6 tubes. I really think its coming from the steels not the magnets, the magnets just let you hear it better especially when they are brighter ones. Totally unquantifiable, unmeasurable voodoo, but its there....

[uvacom]

This is true. You can do the math and show that harmonics are generated by the non-uniform field. In general, for a string vibrating in both horizontal and vertical directions, they tend to distort the wave from a sine towards a sawtooth.

This is not distortion due to the magnetic materials, it's purely due to the geometry of things. (The vibrating arc of the string is not negligible compared to the distance from string to pickup.)

Since the string already has overtones of its own, it's a moot point whether it makes any noticeable difference.

Yes, it's not a distortion due to magnetic materials per se.

But I would think that this could create a significant distortion, because it's not just the fundamental of the string which will generate this distortion. Every harmonic is also contributing to the string's movement, and thus every every harmonic the string generates would then have it's own overtones generated which follows the fourier series for the sawtooth waveform.