Electronic music - pickups: Difference between revisions

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A piezo element (often in disc form, sometimes in others like a guitar pickup's rectangular pellets) responds to bending/stress on its surface with voltage.
A piezo element (often in disc form, sometimes in others like a guitar pickup's rectangular pellets) responds to bending/stress on its surface with voltage.


This makes them useful to sense vibration, impact (they are common in electronic drumkits), and in theory bending.
This makes them useful to sense  
vibration (including sound),  
impact (they are common in electronic drumkits),  
and in theory sense something bending, though there are more robust ways to do that.
 
There are piezo-based kinetic switches - e.g. battery-less RF buttons that operate from the energy you put in.




You can also use them as actuators, but only for ''very'' small movement - small sounds, small actuators in microscopy, maybe some haptic feedback.
You can also use them as actuators, but only for ''very'' small movement - small sounds, small actuators in microscopy, maybe some haptic feedback.


{{comment|(They are seen in some vandal proof buttons, because there can be a serious amount of hard material in between button and piezo. But they are not the only or often even best way to do that.)}}
{{comment|(They are seen in some vandal proof buttons, because there can be a serious amount of hard material in between button and piezo. Yet they are not the only or often even best way to do that.)}}




There are also piezo based kinetic switches - e.g. battery-less RF buttons that operate from the energy you put in.




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Piezo elements put out what you could consider AC.
Piezo elements are polarized in the sense that bending it the same direction way will always put a voltage out the same direction.  
They are polarized only in the sense that bending it the same direction way will always put a voltage out the same direction.
Reversing it will put the waveform the other way.


If you have a single-ended circuit, one way will be into nothing.




If you have a single-ended circuit and want it to work connected either direction {{comment|(e.g. simple ADCs, such as some in microcontrollers)}}, consider a diode rectifier.
When sensing vibration they put out what you could consider AC, and you would still get half of the waves,
This ''will'' mean half the waveform is rectified away, and you lose some sensitivity, so some op amp trickery is sometimes preferred.
and you might not even notice having connected it backwards.
 
 
If you're e.g. measuring impulses, this might not matter much, because unless it dampens ''extremely'' quickly,
you will see either the first or second half of the first oscillation.
Yes, the first part would be a little stronger, and may come it a few milliseconds earlier (their own physical resonance tends to be hundreds of Hz).


For low latency velocity-sensitive drumkits, choosing to care helps a little.  In general, not so much.


If you're measuring impulses, then it matters ''somewhat'', because if a vibration dampens quickly, it ''can'' now matter that you see ''either'' the first part of the firth wave or the second, in that the first part is probably a little stronger, and comes in maybe ~1ms{{verify}} before the second.
For low latency velocity-sensitive drumkits, choosing to care helps a little.


If you have a single-ended circuit and want it to work connected either direction {{comment|(e.g. simple ADCs, such as some in microcontrollers)}}, consider a diode rectifier.
This ''will'' mean half the waveform is rectified away, and you lose some sensitivity, so some biasing and/or op amp trickery is sometimes preferred.


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http://music-electronics-forum.com/t960/
http://music-electronics-forum.com/t960/


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==Electromagnetic pickups==
==Electromagnetic pickups==
{{stub}}
{{stub}}


'''Electromagnetic pickups''', a.k.a. '''magnetic pickups''', means  
'''Electromagnetic pickups''', a.k.a. '''magnetic pickups''', means  
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In the case of a guitar, the vibrations of the string becomes the signal on the coil, pretty directly.
For context: When you move a magnet near a wire, current flows.
This is e.g. how an [https://en.wikipedia.org/wiki/Electric_generator electric generator] works, turning movement into electricity.
 
A guitar does something similar, but instead of moving the magnet near a wire, it moves the wire near a magnet.
 
It's not that the strings are magnetic (that would work, but be hard to make),
it's that that is done by the pickup as well.
The pickup has two distinct parts: magnets, and a coil.
The magnet is there only to set up a field strong enough for the coils to then notice the variation in.  


This is why such guitar pickups only work with metal strings,
A variation caused by the movement of a conductor - the strings.
and do not pick up anything acoustic ''at all'' so the rest of the guitar's design barely matters to the sound.


The vibrations of the string becomes the signal on the coil, ''fairly'' directly.




'''Single coil or humbucker'''
This is also why such guitar pickups only work with metal strings,
and do not pick up anything acoustic, so the rest of the guitar's design barely matters to the sound - except perhaps to
things like
: hitting the body (impacts end up soft vibration of the strings),
: [https://en.wikipedia.org/wiki/Sympathetic_resonance sympathetic vibration] of strings
: shaking a guitar




Coils are by nature an antenna, so are good at picking up any electromagnetism happening nearby,
<!--
the strongest of which is usually the 50Hz / 60Hz power hum.


And this hum can be made worse by certain effects, including distortion, fuzz, compressors <!--(often when they effectively reduce the dynamic range)-->.
Note that there is a difference between
* vibrato while holding a string
:: basically just bending
 
* bending the neck to change the tension
 
* shaking it in a direction that does ''not'' do the last
 
 
 
It should be pointed out that
shaking
and
neck bending
have overlap but also un
 
Shaking the guitar works out as [[vibrato]], because you are bending the neck slightly in a regular pattern
: it's a subtler variant of using a whammy bar, useful if you don't have one.
 
Even vertically shaking an electric guitar seems to work,
so even without bending the neck it seems to also be something sympathetic with the string vibration.
 
 
This works similarly on acoustic,
though note not all necks are equally stiff.
 
On acoustic you may also just get more noticeable change from just pointing the sound box elsewhere
 
 
On damage
 
Remember that there is always a good amount of tension on the neck, from the strings.
 
Varying that slightly should not
 
That's not to say that all bending is the same, and
 
 
 
-->
 
 
===Single coil or humbucker===
 
Coils are by nature an antenna.
 
That makes them good at picking up any electromagnetism happening nearby, the strongest of which is usually the 50Hz / 60Hz power hum.
 
And this hum can be made more noticeable by certain audio effects, including distortion, fuzz, compressors <!--(often when they effectively reduce the dynamic range)-->.
 
<!--
It will pick up anything that produces lower frequencies.
You largest saving grace is distance - an [[inverse square]] thing.
 
Say, put an electric screwdriver/drill next to it and you'll hear its motor,
but move it away and it easily falls below other noise.
 
Actually anything digital. even if the communication is at a much higher frequency,
particularly digital transmission tends to be low -- and that 'sending or not'
 
E.g. the The [[elektrosluch]] lets you record baseband EM as sound -- and is nothing more than a coil and an amplifier.
 
-->




The simplest pickup is a '''single-coil''' pickup, which don't address this at all.
The simplest pickup is a '''single-coil''' pickup, which don't address this at all.
There are some ways to reduce hum (e.g. don't be near a powered object), but not by a lot.




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* and one with its magnets flipped.
* and one with its magnets flipped.


You can work this out on paper if you want, but practically, due to being hooked up opposite,
This is a clever trick, but it involves two parts, so if you want to actually understand them, you probably want to work this out on paper.
anything that both parts of the pickup pick up the same amount ends up being subtracted from that other near-copy.
 


It's far from perfect, not least because of the varying position, but it's pretty decent for things that further away and low frequency - and mains hum is that.
Due to being hooked up opposite, anything that both coils in the pickup receive the same amount ends up being subtracted.


The movement from the nearby string, on the other end, will end up being picked up opposite (due to the flipped magnetics in the pickup) so that subtraction ends up being addition again.
So why doesn't that happen to the strings as well?
That's where the other part comes in: due to one coil having the magnets flipped, the signal from these coils are idential but one of them is flipped - and subtracting a wave from it's flipped form works out as addition again.
 
 
And yeah, that subtraction is far from perfect for a few reasons (e.g. the fact that the coils cannot be in ''entirely'' the same place),
but it's pretty decent for lower frequencies, and sources that are further away.
Mains hum is both of those, so it works pretty well.




{{comment|Technically, you can connect humbuckers either in series or in parallel,  
{{comment|Technically, you can connect humbuckers either in series or in parallel,  
but series is more typical due to the output signal (and the effect{{verify}}) being a little stronger.}}
but series is more typical due to the output signal (and the hum-reducing effect{{verify}}) being a little stronger.}}




Single coils tend to be brighter (and used in surf, guitar, sixties sounds), humbuckers tend to be bassier.
Single coils tend to work out a little brighter (and used in surf, sixties sounds), humbuckers tend to be bassier.


And then there are distinct designs of each.
And then there are distinct designs of each.


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Is there merit to the "more magnet means less natural" ?
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===Individual pole or rail===
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This isn't a difference in the coils (usually), it's a difference in the magnets{{verify}}
Most pickups have little circuits. Those are effectively the ends of magnets.
Why give each string its own pole?


It's not actually necessary - as long as there's a strong enough magnetic field near all strings,
it'll work fine. 
I've seen plenty of basses that just throw two pickups under apparently purely because one wasn't wide enough (they are still wired as single coil).
In a way, rail pickups do that same thing but are a little more honest about it: they have one long conductor getting that magnetic field out there.




'''Individual pole or rail'''
<!--


There is a distinction between
Is there a difference? Sure.  
* having individual poles under the strings
: closer poles mean you have more control of focusing the magnetics on the string, meaning somewhat stronger output
: and when poles are screws, you can position it closer, per string
:: ...and you may care to do that to change the relative volume of each string)


* rail pickups, which have one long conductor do the same thing
Individual poles under the strings may (or may not) be screws that let you extend these to put them closer to the strings,
focusing the magetic field and making for somewhat stronger output - or lower noise if you dial down the volume.
And the ability to do that per string lets you alter the relative volume of each string a bit, e.g. if you feel the lowest string is


Rail pickups doesn't do as much focusing, probably a little lower signal to noise, but also don't go quieter when bending
From that explanation, you can expect rail pickups to maybe be a little lower signal to noise.
:: but can be made as small as a single coil, meaning you can install in guitars designed for one-coil witout modifying them
That said, they run less risk of becoming quieter when bending a string (further up the neck).
:: and allow bending strings without volume loss


And as a footnote, you might get humbucking rail pickups as small as a single coil,
meaning you can install in guitars designed for one-coil witout modifying them
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'''Passive or active?'''
===Passive or active===
<!--
<!--
Active pickups (a.k.a. hot pickups?) are any that are powered, whatever the style {{verify}}
Active pickups (a.k.a. hot pickups?) are any that are powered, whatever the style {{verify}}


Pickups give enough signal that they do not need to be powered,
Pickups give enough signal that they do not need to be powered  
yet amplifying that signal closer to the source avoids some loss and noise issues,
for circuits to receive what they do -- yet placing the amplification (and more importantly, impedance change)
close to the signal generation avoids some loss and noise issues,
and that motivation is also why active pickups are usually humbuckers.
and that motivation is also why active pickups are usually humbuckers.


-->
-->




 
===Coil tap or split coil===
<!--
 
'''Coil tap or split coil?'''
<!--
<!--


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===The circuit behind the dials===
<!--
The volume dial is typically just a pot that wipes between ground on one side, and the coil output on the other.
Log-scale, because that makes more sense for volume.
The tone pot is more interesting.
One basic construction is, basically independent of the volume dial,
to have the coil output on one side of another pot, with the wiper going to ground via a capacitor, the other will be unconnected.


'''Does that make all electric guitars sound the same?'''
This is a basic RC lowpass circuit, with the pot on the unconnected side introducing so much resistance that this part has no effect.
 
With a ~200kOhm pot, a ~dozen-nF capacitor works.{{verify}}
 
 
Wire to potmeter case is trying to lessen hum a little by shielding it.
 
 
 
https://www.youtube.com/watch?v=6OcmKU5rblA
 
-->
 
===Multiple pickups, position, and switches===
<!--
 
The idea is that
putting a pickup near the neck makes for a sharper tone, and
putting it near the fretboard ('bridge pickup') make fir a more mellow and warm sound.
[https://youtu.be/Iy9jEy6nLek?t=95 This is one of the nicest demonstrations I've found]
 
 
'''Assuming you have both (or three)'''
 
{{imagesearch|resonant string|A vibrating string physically moves more near the center of the string}},
so putting a pickup there will also be ''louder'' than putting that same pickup further away.
 
That said, in guitars with both neck and bridge pickup, one may well be more sensitive than the other,
so you can combine them with more tone than volume difference.
 
As a side effect, the neck pickup being hotter works out as lower-noise.
 
 
There is not necessarily an EQ difference {{verify}}, but
 
 
 
The classical switch is engages one at a time, but guitarists found use in moving it to engage two at once,
so on 2-pickup you may have 2-way or 3-way{{verify}}, and on 3-pickup you may have 3-way and 5-way.
 
 
-->
 
 
<!--
===Are you saying all electric guitars sound the same?===


Given that a magnetic pickup only picks up the string and nothing acoustic,
Given that a magnetic pickup only picks up the string and nothing acoustic,
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-->


 
===DIY pickups===
'''DIY pickups'''
<!--
 
You ''can'' wind your own pickups.  
You ''can'' wind your own pickups.  
There's a bunch of math involved,  
There's a bunch of math involved,  
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===Single coil hum===
===More on single coil hum===


<!--
<!--


Single coil is a decent antenna, and pretty good at picking up environmental EM, which is often mostly mains hum 50 or 60Hz).
Single coil is a decent antenna, and pretty good at picking up environmental EM, which is often mostly mains hum 50 or 60Hz).




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That doesn't mean all guitars are equally noisy, or that you can't so anything about it.
That doesn't mean all guitars are equally noisy, or that you can't so anything about it.
Turn off mains devices, or stay some distance away from them
You can shield the pickups. This probably affects the sound, though.
You can get a 'hum eliminator pedal', which is mainly just a notch filter
"noise reduction pickups"
All metal parts are connected together - bridge (and thereby strings), and possibly the pick outside,
probablty the the potmeters - and all connected to the




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: at some point it's so close that fretting a string and/or vibration of a fretted string will hit it
: at some point it's so close that fretting a string and/or vibration of a fretted string will hit it
: this doesn't reduce the hum, it just means the signal is a bit stronger so when you turn it to the same volume, the noise is a little lower.
: this doesn't reduce the hum, it just means the signal is a bit stronger so when you turn it to the same volume, the noise is a little lower.
'''If you have multiple pickups and a switch, and only some pickups have hum''', it's probably damaged




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It is.
It is.
Y'all don't like the solution, though.
Y'all don't like the solution, though.


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-->
-->


===Sustainers===
===Sustainers===
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The {{imagesearch|E-bow sustainer|E-bow}} is one brand of hand-held sustainer, aimed to work on one string, to add expressiveness to phrasing.  
The {{imagesearch|E-bow sustainer|E-bow}} is one brand of hand-held sustainer, aimed to work on one string, to add expressiveness to phrasing.  
It has a groove to rest on one string (that you're not playing) to help align and pivot is to modulate the effect, the other to indicate where it picks up and excites.
It has grooves to the side to rest on other strings you're not playing, and indicates where it most picks up and excites.


Its designer found that if you reverse the driver coil, it dampens the fundamental frequency and amplifies overtones/harmonics a bit more. This is presumably all that the harmonics switch does.
Its designer found that if you reverse the driver coil, it dampens the fundamental frequency and amplifies overtones/harmonics a bit more. This is presumably all that the harmonics switch does.
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Sustainiac
Sustainiac


-->
==="Magnetic picks"===
<!--
At one point there was a product called a magnetic pick.
If they called it a modulating pick or ducking pick it would have been fine,
but because they weren't clear about it did,
and because of what the demonstration videos showed,
this got lots of people assuming you could play without touching.
And that does not work.
Knowing the physics of guitars, this makes little sense.
Yes, the entire thing involves magnetic fields, but the magnetic field is just there to have the other part of the pick something to notice.
It is not the magnetic field that vibrates to produce a signal, it is the strings.
If the pick cannot make the strings move, why does it seem to work?
Because it does the opposite of playing:
it effectively deafens the pickup when the magnet is close (a saturation that works out as compression?{{verify}}).
That ''does'' let you add a sort of tremolo effect after you have already physically picked a string,
and that is what all the demonstrations are doing.
Some of them hide this by effectively doing hammer-ons on the neck, others are just having fun.
It's a potentially useful effect, but it's not picking.
https://www.youtube.com/watch?v=x9MF60ZO8rI
-->
-->


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Circuit-wise, piezos can be seen as vibration sensors in parallel with a reasonable capacitor.
Circuit-wise, piezos can be seen as vibration sensors in parallel with a reasonable capacitor.
While they produce reasonable voltage, but their current is low and their output impedance high,
 
and it's part of their design so unavoidable.
While they produce reasonable voltage,  
their current is low and their output impedance high,
which are properties of their physical design,
so largely unavoidable.




This means you want a buffer, and possibly to amplify, or tame, the signal level.
This means you want a [[buffer amplifier|buffer]], and possibly to amplify, or tame, the signal level.


Without such amplification, the level is not very predictable but may work for a particular case - but the  capacitance will almost certainly eat the bass range (it works out as a lowpass filter).
Without such amplification, the level is not very predictable but may work for a particular case - but the  capacitance will almost certainly eat the bass range (it works out as a lowpass filter).




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Many circuits you'll find out there are for guitars, meaning they use a 9V battery they divide.
Many circuits you'll find out there are for guitars, meaning they use a 9V battery they divide.
That circuit consists mostly of
That circuit consists mostly of
* capacitor (for AC coupling, and the bias)
* capacitor (for [[AC coupling] and bias)
* division of the power rails (to bias positive)
* division of the power rails (to bias positive)
* transistor, or op amp
* transistor, or op amp

Latest revision as of 23:24, 8 September 2023

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Piezo elements

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

A piezo element (often in disc form, sometimes in others like a guitar pickup's rectangular pellets) responds to bending/stress on its surface with voltage.

This makes them useful to sense vibration (including sound), impact (they are common in electronic drumkits), and in theory sense something bending, though there are more robust ways to do that.

There are piezo-based kinetic switches - e.g. battery-less RF buttons that operate from the energy you put in.


You can also use them as actuators, but only for very small movement - small sounds, small actuators in microscopy, maybe some haptic feedback.

(They are seen in some vandal proof buttons, because there can be a serious amount of hard material in between button and piezo. Yet they are not the only or often even best way to do that.)



On piezo polarisation

Electromagnetic pickups

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.


Electromagnetic pickups, a.k.a. magnetic pickups, means

  • a coil,
  • close to a permanent magnet (practically often around, it's useful positioning),
  • with both oriented and positioned so that a nearby conductor moving in that field affects the field in a way that makes it into the coils


For context: When you move a magnet near a wire, current flows. This is e.g. how an electric generator works, turning movement into electricity.

A guitar does something similar, but instead of moving the magnet near a wire, it moves the wire near a magnet.

It's not that the strings are magnetic (that would work, but be hard to make), it's that that is done by the pickup as well. The pickup has two distinct parts: magnets, and a coil. The magnet is there only to set up a field strong enough for the coils to then notice the variation in.

A variation caused by the movement of a conductor - the strings.

The vibrations of the string becomes the signal on the coil, fairly directly.


This is also why such guitar pickups only work with metal strings, and do not pick up anything acoustic, so the rest of the guitar's design barely matters to the sound - except perhaps to things like

hitting the body (impacts end up soft vibration of the strings),
sympathetic vibration of strings
shaking a guitar



Single coil or humbucker

Coils are by nature an antenna.

That makes them good at picking up any electromagnetism happening nearby, the strongest of which is usually the 50Hz / 60Hz power hum.

And this hum can be made more noticeable by certain audio effects, including distortion, fuzz, compressors .


The simplest pickup is a single-coil pickup, which don't address this at all. There are some ways to reduce hum (e.g. don't be near a powered object), but not by a lot.


People then thought up humbuckers, a setup that takes

  • two such coils,
  • hooked up in opposite polarity,
  • and one with its magnets flipped.

This is a clever trick, but it involves two parts, so if you want to actually understand them, you probably want to work this out on paper.


Due to being hooked up opposite, anything that both coils in the pickup receive the same amount ends up being subtracted.

So why doesn't that happen to the strings as well? That's where the other part comes in: due to one coil having the magnets flipped, the signal from these coils are idential but one of them is flipped - and subtracting a wave from it's flipped form works out as addition again.


And yeah, that subtraction is far from perfect for a few reasons (e.g. the fact that the coils cannot be in entirely the same place), but it's pretty decent for lower frequencies, and sources that are further away. Mains hum is both of those, so it works pretty well.


Technically, you can connect humbuckers either in series or in parallel, but series is more typical due to the output signal (and the hum-reducing effect(verify)) being a little stronger.


Single coils tend to work out a little brighter (and used in surf, sixties sounds), humbuckers tend to be bassier.

And then there are distinct designs of each.


Individual pole or rail

Passive or active

Coil tap or split coil

Multiple pickups, position, and switches

DIY pickups

More on single coil hum

Sustainers

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.


A guitar sustainer is an electromagnetic pickup coil, plus amplifier and driver coil.


It sends out what it receives (due to typical design largely focuses on lower frequencies), which on a guitar amounts to forcedly resonating the tone currently being played.


Sustainers are often sold as separate products.

Some guitars have sustainers built in (this is often custom), which will often look like regular pickups, and could even be used as a pickup when not active, should you want to.


Sustainers are often used for spacey sounds or other genre-specific things, because while it's good at controlling slow volume swells, tremolo, and some other expressiveness that you otherwise cannot easily do on guitars (and are more commonly associated with other instruments, like violins - which is e.g. where the e-bow gets its name), the same long sustains don't combine too well with strumming or fast playing.


The E-bow is one brand of hand-held sustainer, aimed to work on one string, to add expressiveness to phrasing. It has grooves to the side to rest on other strings you're not playing, and indicates where it most picks up and excites.

Its designer found that if you reverse the driver coil, it dampens the fundamental frequency and amplifies overtones/harmonics a bit more. This is presumably all that the harmonics switch does.





"Magnetic picks"

Noise

Preamps

Piezo pickup amps

Magnetic pickup amps

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