Piezo pickups and distortion

Post by philicorda
On two separate occasions recently I have recorded ukuleles, and taken
their little piezo pickups as well as a mic.
With my behringer DI they both sounded a bit noisy and lacking in
brightness, but clean. So I plugged them into the DI on my focusrite
ISA200 and there was much less noise, more top end, but they sounded
distorted.

You may have been hearing the pickup rattling around. The better
resolution of the Focusrite allowed you to hear what the Behringer
didn't. Cheap pickups are often like that.

If you upload your test file to a site that doesn't require installing
a program in order to access it (and the ensuing advertising) I'd take
a listen to it. Rapidshare or Sendspace at the obvious web sites.

philicorda

2008-01-06 01:57:35 UTC

You may have been hearing the pickup rattling around. The better
resolution of the Focusrite allowed you to hear what the Behringer
didn't. Cheap pickups are often like that.

Possible I guess. They were real cheap pickups too. It sounds more fuzzy
to me though.

Post by Mike Rivers
If you upload your test file to a site that doesn't require installing a
program in order to access it (and the ensuing advertising) I'd take a
listen to it. Rapidshare or Sendspace at the obvious web sites.

I don't think you need a program for that site. Anyway, here's another
link:
http://rapidshare.com/files/81602008/uke.wav.html

Mike Rivers

2008-01-06 04:22:27 UTC

Post by philicorda
I don't think you need a program for that site. Anyway, here's another
link:http://rapidshare.com/files/81602008/uke.wav.html

When you click on the Fast Files link you posted, a window comes up
with the following statement:

"By clicking "Continue," I represent that I (1) am at least 18, (2)
agree to the EULA and Privacy Policy terms and (3) consent to install
Zango and access www.fast-files.com."

Anyway, I listened to the one at Rapidshare on the Minimus 7 speakers
that I have connected to the computer. It sounds just like a uke to
me. I'll give it a more careful listen when I move the file someplace
with better gear, but I don't hear anything worrysome yet.

geezer

2008-01-06 12:29:31 UTC

Post by philicorda
I don't think you need a program for that site. Anyway, here's another

Mike,

you have minimus 7s??? If they're the made-in-japan version, you are
my hero! Those little speakers were one of the great audio bargains
of all time.

-glenn

Post by philicorda
link:http://rapidshare.com/files/81602008/uke.wav.html

When you click on the Fast Files link you posted, a window comes up
"By clicking "Continue," I represent that I (1) am at least 18, (2)
agree to the EULA and Privacy Policy terms and (3) consent to install
Zango and accesswww.fast-files.com."
Anyway, I listened to the one at Rapidshare on the Minimus 7 speakers
that I have connected to the computer. It sounds just like a uke to
me. I'll give it a more careful listen when I move the file someplace
with better gear, but I don't hear anything worrysome yet.

Mike Rivers

2008-01-06 12:37:18 UTC

Post by geezer
you have minimus 7s??? If they're the made-in-japan version, you are
my hero! Those little speakers were one of the great audio bargains
of all time.

In the interest of getting off topic within 12 hours, I'll answer.

Mine say "Custom made in Malasia" so I guess I'm not your hero any
more. They're sort of mongrels, though. One blew a tweeter after Radio
Shack stopped selling replacements. I posted a "does anyone have...?"
message here and a kind soul sent me a pair. I replaced one tweeter
and it sounded enough different from the other speaker that I replaced
the tweeter in the other speaker, and I think I may have replaced a
woofer as well. I've had these for at least 20 years.

I used to take them out on remotes but now they're just hooked up to a
cheap Technics receiver in my home office and mostly they get used for
listening to "the radio" when I'm working at the computer.

philicorda

2008-01-06 15:23:43 UTC

Post by philicorda
I don't think you need a program for that site. Anyway, here's another
link:http://rapidshare.com/files/81602008/uke.wav.html

When you click on the Fast Files link you posted, a window comes up with
"By clicking "Continue," I represent that I (1) am at least 18, (2)
agree to the EULA and Privacy Policy terms and (3) consent to install
Zango and access www.fast-files.com."

The bastards.
I could not work out what was going on there for a bit.
I then switched the user agent of my browser from Mozilla-Linux to IE7-
Vista and I get the window you are talking about.
There is absolutely no reason for it, as with browser identifier Mozilla-
Linux you go straight to the download page.

Anyway, I listened to the one at Rapidshare on the Minimus 7 speakers
that I have connected to the computer. It sounds just like a uke to me.
I'll give it a more careful listen when I move the file someplace with
better gear, but I don't hear anything worrysome yet.

Try this one too (855KB 44.1KHz 24 bit):
http://rapidshare.com/files/81725223/uke2.wav.html
Different uke, different crap piezo pickup, to my ears the same problem.

Don Pearce

2008-01-06 10:22:46 UTC

Post by philicorda

You may have been hearing the pickup rattling around. The better
resolution of the Focusrite allowed you to hear what the Behringer
didn't. Cheap pickups are often like that.

Possible I guess. They were real cheap pickups too. It sounds more fuzzy
to me though.

I don't think you need a program for that site. Anyway, here's another
http://rapidshare.com/files/81602008/uke.wav.html

OK, a few things. First there is a bit of 50Hz hum that needs getting
rid of. You can deal with it pretty effectively with a highpass filter
set a bit below 200Hz.

For the rest, this uke sound is very amenable to eq. About a 4dB lift
at 330Hz puts some meat into it, and 6dB at 10kHz makes it ring more
brightly. There is a sort of "tizz" to the recording that may be
something loose and rattling, but I couldn't identify it.

But whatever it is you have here, it makes a very good uke sound -
just needs refining.

d

--
Pearce Consulting
http://www.pearce.uk.com

philicorda

2008-01-06 15:40:51 UTC

On Sun, 06 Jan 2008 10:22:46 +0000, Don Pearce wrote:

<snip>

Post by Don Pearce
OK, a few things. First there is a bit of 50Hz hum that needs getting
rid of. You can deal with it pretty effectively with a highpass filter
set a bit below 200Hz.
For the rest, this uke sound is very amenable to eq. About a 4dB lift at
330Hz puts some meat into it, and 6dB at 10kHz makes it ring more
brightly. There is a sort of "tizz" to the recording that may be
something loose and rattling, but I couldn't identify it.

I'll give that a go. Most tracks I can use the mic, but the ukulele is so
quiet that the spill from the rest of the band is annoying.

Post by Don Pearce
But whatever it is you have here, it makes a very good uke sound - just
needs refining.
d

Don Pearce

2008-01-06 18:56:43 UTC

Post by philicorda

Post by Don Pearce
For the rest, this uke sound is very amenable to eq. About a 4dB lift at
330Hz puts some meat into it, and 6dB at 10kHz makes it ring more
brightly. There is a sort of "tizz" to the recording that may be
something loose and rattling, but I couldn't identify it.

I'll give that a go. Most tracks I can use the mic, but the ukulele is so
quiet that the spill from the rest of the band is annoying.

Here's what I have in mind:

http://81.174.169.10/odds/uke.wav

d

--
Pearce Consulting
http://www.pearce.uk.com

Scott Dorsey

2008-01-06 13:54:57 UTC

Post by philicorda
So I guess the different impedance had something to do with it, but why
distortion? Do piezo pickups get non linear depending on the load they
are plugged into?

They are incredibly nonlinear under the best of circumstances, and any
load you add to them makes them much worse. Figure 1M minimum, 10M better.
And yes, you can often tell the difference in sound between a 10M and 100M
source with those damn things. They are evil.

The plastic piezo materials are better in this regard than the old ceramics
but they still aren't great.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

philicorda

2008-01-06 15:37:55 UTC

Post by philicorda
So I guess the different impedance had something to do with it, but why
distortion? Do piezo pickups get non linear depending on the load they
are plugged into?

They are incredibly nonlinear under the best of circumstances, and any
load you add to them makes them much worse. Figure 1M minimum, 10M
better. And yes, you can often tell the difference in sound between a
10M and 100M source with those damn things. They are evil.

Ok, so higher impedance the better. Are there any really high impedance
DI boxes out there? Or something easy I can build. Using the focusrite
means pulling it from the rack and taking it to the live room, which is a
pain.

The weird thing is that I'm still sure the behringer one was less
distorted, though noisier and duller. It seems unlikely now, as looking
at the specs, the ISA220 input is 1M and the behringer says "Input
resistance >250K".

Post by Scott Dorsey
The plastic piezo materials are better in this regard than the old
ceramics but they still aren't great.
--scott

Scott Dorsey

2008-01-06 16:01:47 UTC

Post by philicorda
Ok, so higher impedance the better. Are there any really high impedance
DI boxes out there? Or something easy I can build. Using the focusrite
means pulling it from the rack and taking it to the live room, which is a
pain.

The Countryman is the normal one that most folks use. I did a DIY DI project
for Recording magazine once... two transistors and a couple resistors, 10M
input impedance. No transformer isolation, but it's designed for just the
kind of thing you're doing.

Post by philicorda
The weird thing is that I'm still sure the behringer one was less
distorted, though noisier and duller. It seems unlikely now, as looking
at the specs, the ISA220 input is 1M and the behringer says "Input
resistance >250K".

This would make me think that the problem is something vibrating around
in the insturment. Either the pickup itself, or part of the instrument
body. With the lower-Z load on the thing, you lose all your high end
and consequently you can no longer hear the problem. You can do a more
effective job with a high-Z DI and a parametric EQ to kill the buzz.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

philicorda

2008-01-16 01:20:17 UTC

The Countryman is the normal one that most folks use. I did a DIY DI
project for Recording magazine once... two transistors and a couple
resistors, 10M input impedance. No transformer isolation, but it's
designed for just the kind of thing you're doing.

The March 1998 Recording magazine seems to be out of back issues, sadly.
That Countryman one looks good.

It's possible both ukuleles were making acoustic buzzing noises, though I
seem to hear it more like low level electrical distortion.

Next time I have a chance I'll compare a low and high impedance DI, and
see if the distortion is audible when I boost the top end on the low
impedance one.
I still have the crazy idea that some piezo pickups might be more linear
into a low impedance load.

Post by Scott Dorsey
--scott

Scott Dorsey

2008-01-16 01:47:53 UTC

Post by philicorda

The Countryman is the normal one that most folks use. I did a DIY DI
project for Recording magazine once... two transistors and a couple
resistors, 10M input impedance. No transformer isolation, but it's
designed for just the kind of thing you're doing.

The March 1998 Recording magazine seems to be out of back issues, sadly.

Folks can still call 1-303-516-9118 and get a reprint sent to them either
on paper or .pdf format for a couple bucks.

Post by philicorda
That Countryman one looks good.

It is, and not only goes the Countryman have a high input impedance, it
also has transformer isolation. So you get the best of both worlds (although
if you want to break grounds you have to use an internal battery).

Post by philicorda
It's possible both ukuleles were making acoustic buzzing noises, though I
seem to hear it more like low level electrical distortion.

If you like ukulele lady, ukulele lady like-a you.

Post by philicorda
Next time I have a chance I'll compare a low and high impedance DI, and
see if the distortion is audible when I boost the top end on the low
impedance one.
I still have the crazy idea that some piezo pickups might be more linear
into a low impedance load.

Try it and see. The worst that can happen is it'll sound bad. Take a
high-Z DI and add a shunt resistor across it, so you can reduce the
impedance without changing anything else. If you add a 100K shunt across
it, does it sound better or worse? I'm guessing it'll sound worse, but
if it sounds better, that would be exciting.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Peter Larsen

2008-01-12 13:18:35 UTC

A piezo appears in a circuit as a capacitor. Toss in a cable with a bit of
reactance or a transformer loading and you have an electrical resonator.

Post by philicorda
Not in a clipped way, but quite the opposite as though it was just the
low level stuff that was getting distorted.
Here's a clip of the focusrite DI. (1MB 44.1Khz 24bit PCM Wav).
http://www.fast-files.com/getfile.aspx?file=5367

and on http://rapidshare.com/files/81602008/uke.wav.html

which is where I got it and listened briefly on the laptops speakers. On
those it is excellent.

Post by philicorda
I didn't keep a recording the cleaner noisier behringer DI
unfortunately.
So I guess the different impedance had something to do with it, but
why distortion? Do piezo pickups get non linear depending on the load
they are plugged into?

They ARE non linear by definition. The example is too short to reliably
extract a best guess of its frequency response, but it has a problem at 8117
Hz, try to dip the closest slider on a fairly narrow eq 6 to 12 dB or de-ess
at that exact center frequency, assuming the de-ess frequency of whatever
contraption you have avaiable is adjustable.

And do something about that 50 Hz hum .... possibly indicative of the piezo
needing a buffer amp within inches of wiring instead of furlongs. Seems to
me that it would unavoidably need one anyway to be certain of having the
optimum load.

That Behringer DI, was it active or passive? ... I have a recording of
singer with a grand and then with an electric piano (two consecutive
concerts) coming up, and thinking about getting a couple of their ULTRA-DI
400P, seems to me that it will offer transformer coupling, and I like that
concept when interfacing with unknown musicians equipment. Or should I
simply mic the unknown piano loudspeaker ... if it was known good that would
be my choice, but with it being undefined I prefer to keep my options open.

Kind regards

Peter Larsen

Jay Ts

2008-01-12 18:19:19 UTC

Post by Peter Larsen
A piezo appears in a circuit as a capacitor.

It is more than a capacitor, but I think you're trying
to say that it acts a lot like one. Typical piezo transducers
have small capacitances and very high DC resistance, on
the order of several megaohms. (A sample I tested just now
is about .01 uF at 40 Mohms.)

They put out a very weak signal, that is susceptible
to picking up EMF and other noise. It's important to
have good shielding around the wires leading to the
transducer, and if possible, the transducer itself.
The wires should be short, and connect to a preamp
with a high-impedance (e.g, FET) input.

Post by Peter Larsen

Post by philicorda
So I guess the different impedance had something to do with it, but why
distortion?

The way piezo transducers function is not all that unlike the
elements in capacitor microphones do. They're different in that they
pick up the vibration from solid objects, rather than from air.
That means you'll get a different kind of sound from them.

I wasn't able to get the .wav file from Rapidshare, so
I can't comment on it. So I'm guessing that maybe at
least part of what you're calling "distortion" may
simply be a different sound that you hear when listening
to the uke with your ears, or through a microphone.

Don't expect the piezo transducer to sound exactly that
way. The transducer will give you a sound that is _like_
acoustic, but not the same.

Aside from that, any really obvious "distortion" might
be due to the transducer not being stuck on the instrument,
and it could be resonating (buzzing). Or maybe it's just
broken - the quartz wafer in the transducer is fragile
and cracks very easily when the transducer is bent. If
that has happened many times, it may affect the sound.

Piezo transducers also have a resonance that is often
in audio frequencies (1.5 KHz for a big one, and a few
KHz for smaller sizes) and you may want to try a parametric
equalizer to find the resonant frequency and put a narrow,
band-reject filter on it at say, -4 dB. Play with it and
find the best settings.

Jay Ts

--
To contact me, use this web page:
http://www.jayts.com/contact.php

Jenn

2008-01-12 19:04:38 UTC

Post by Jay Ts

Post by Peter Larsen
A piezo appears in a circuit as a capacitor.

It is more than a capacitor, but I think you're trying
to say that it acts a lot like one. Typical piezo transducers
have small capacitances and very high DC resistance, on
the order of several megaohms. (A sample I tested just now
is about .01 uF at 40 Mohms.)
They put out a very weak signal, that is susceptible
to picking up EMF and other noise. It's important to
have good shielding around the wires leading to the
transducer, and if possible, the transducer itself.
The wires should be short, and connect to a preamp
with a high-impedance (e.g, FET) input.

Post by Peter Larsen

Post by philicorda
So I guess the different impedance had something to do with it, but why
distortion?

In the acoustic guitar world, the piezo under-the-saddle pickup is
mostly considered to be a necessary evil. The positives are that it is
consistent from string to string as to volume and tone, because the
string pressure through the saddle to the piezo element is fairly
consistent from string to string. The problems include a tendency
toward a mid-range bump commonly call "the piezo quack". Most annoying.
Many of us use the a piezo in conjunction with a soundboard transducer,
which calms the quack, though it can be prone to feedback. I commonly
use a blend of about 80% soundboard transducer and 20% piezo. Some also
use an in-the-guitar mic as part of the blend. Other of us use a piezo
in conjunction with an effect pedal, such as the Fishman Aura.

Jay Ts

2008-01-12 19:40:08 UTC

Post by Jenn

Don't expect the piezo transducer to sound exactly that way. The
transducer will give you a sound that is _like_ acoustic, but not the
same.

Oops, instead of "like acoustic", I meant "like a microphone". (I'm
used to using piezos on electric guitar. ;-)

Post by Jenn
In the acoustic guitar world, the piezo under-the-saddle pickup is
mostly considered to be a necessary evil. [..] The problems
include a tendency
toward a mid-range bump commonly call "the piezo quack".

That's probably due to the piezo's resonance. Have you tried using
a parametric equalizer to tame that? Using a good equalizer with
just the right settings might work better and more simply than
adding more transducers, mics and other effects.

I'm a proponent of fixing problems at the source, before
adding more complexity.

Jay Ts

--
To contact me, use this web page:
http://www.jayts.com/contact.php

hank alrich

2008-01-12 20:13:13 UTC

Post by Jay Ts
That's probably due to the piezo's resonance. Have you tried using
a parametric equalizer to tame that? Using a good equalizer with
just the right settings might work better and more simply than
adding more transducers, mics and other effects.

The piezo quack is not fixable by EQ. EQ can help, but it won't
eliminate that particular aspect of the sound

Post by Jay Ts
I'm a proponent of fixing problems at the source, before
adding more complexity.

Which, to me, means using a K&K pickup.

http://www.kksound.com/

This makes a world of difference, IME.

--
ha
Iraq is Arabic for Vietnam

Jenn

2008-01-12 23:23:59 UTC

Post by Jay Ts

Post by Jenn

Don't expect the piezo transducer to sound exactly that way. The
transducer will give you a sound that is _like_ acoustic, but not the
same.

Oops, instead of "like acoustic", I meant "like a microphone". (I'm
used to using piezos on electric guitar. ;-)

I've never heard the quack tamed by EQ alone, sadly.

Post by Jay Ts
I'm a proponent of fixing problems at the source, before
adding more complexity.

As am I, when possible ;-)

Post by Jay Ts
Jay Ts

hank alrich

2008-01-12 20:13:12 UTC

Post by Jenn
In the acoustic guitar world, the piezo under-the-saddle pickup is
mostly considered to be a necessary evil.

And IMO is rendererd obsolete byt the pickups from K&K.

--
ha
Iraq is Arabic for Vietnam

Jenn

2008-01-12 23:22:29 UTC

Post by hank alrich

Post by Jenn
In the acoustic guitar world, the piezo under-the-saddle pickup is
mostly considered to be a necessary evil.

And IMO is rendererd obsolete byt the pickups from K&K.

I'm not a member of the K&K fan club, but they and other sound board
transducers are indeed my favorites, which is why I blend mine in at
about 80%. I'm not ANTI K&K, by the way, I think they sound great, but
no better than other SBTs.

In the piezo arena, B-Band's is quite better than any others I've heard
due, they say, to their use of a unique crystal. (disclosure: I'm an
endorser for them).

Mike Rivers

2008-01-12 23:37:19 UTC

Post by Jenn
In the piezo arena, B-Band's is quite better than any others I've heard
due, they say, to their use of a unique crystal. (disclosure: I'm an
endorser for them).

I heard those at the NAMM show a couple of years back and thought that
they sounded good enough for just about any live sound use. I figured
that they had some equalization built in.

Unique crystal, eh?

Jenn

2008-01-12 23:46:50 UTC

In article

Post by Jenn
In the piezo arena, B-Band's is quite better than any others I've heard
due, they say, to their use of a unique crystal. (disclosure: I'm an
endorser for them).

That's what they say; I don't really know anything more than that. I
just play ;-)

Mike Rivers

2008-01-13 01:36:32 UTC

Post by Jenn
That's what they say; I don't really know anything more than that. I
just play ;-)

What they say on the web site is: "Note! B-Band UST and AST pickups
use a unique sensor technology and will only work with B-Band
preamps."

It's not a piezoelectric pickup, it's a variable capacitance sensor,
kind of like a condenser mic, sort of. [ooohhh! ahhhhhh!]

Jay Ts

2008-01-13 20:14:24 UTC

Post by Jenn
In the piezo arena, B-Band's is quite better than any others I've heard
due, they say, to their use of a unique crystal. (disclosure: I'm an
endorser for them).

I made a quick visit to their website, and they say:

| All B-Band pickups use our proprietary patented electret film
| technology! B-Band pickups do not use common piezo material

I think this is the plastic film that IIRC was introduced
around the late 1980s. Or at least that's when I first
remember seeing it (in the electronics industry, not yet
in the music and audio fields).

I got a sample from the company, and regretably, did not
at the time have a way of putting it to use. (I suppose I
missed a nice business opportunity there.)

I remember that the technology (in concept) seemed
clearly superior to using piezo (quartz) crystals.
Like piezo transducers, it generates an electric signal
when the material vibrates or is deformed. Other than that,
it has very different physical properties, and as a result,
doesn't suffer from the same limitations of quartz wafers.

It might be worth a try on that ukelele. (?)

Jay Ts

--
To contact me, use this web page:
http://www.jayts.com/contact.php

Paul Stamler

2008-01-13 06:44:48 UTC

One thing some folks do is to mount both a piezo (w. high-Z preamp) and a
microphone in the guitar. The mic goes to the house, the piezo goes to the
monitors. Less trouble with feedback (not none, but less) and the audience
doesn't have to listen to the piezo. Problem is, you do.

Peace,
Paul

Mike Rivers

2008-01-12 20:59:40 UTC

Post by Jay Ts
They put out a very weak signal, that is susceptible
to picking up EMF and other noise. It's important to
have good shielding around the wires leading to the
transducer

Actually, they put out quite a high voltage - piezo transducers are
used to make a the spark in cigarette and fireplace lighters, and
they're used to replace the traditional inductor/autotransformer
"spark coil" for the spark plugs of a small engine like a chain saw or
lawn mower. Because their source impedance is so high, however, you
need a very high impedance input amplifier for a piezo pickup.
Otherwise, most of the voltage will be dropped across the transducer
itself and not the amplifier input. Because of the high impedance at
the end of the wire, it does tend to make a pretty good antenna,
though unlike a magnetic pickup, the piezo pickup itself is
insensitive to magnetic fields.

Post by Jay Ts
The way piezo transducers function is not all that unlike the
elements in capacitor microphones do.

Not really. A piezoelecttric transducer generates a voltage when it's
deformed. A condenser mic changes capacitance, which results in a
change in the voltage between two electrically charged plates. A
condenser microphone depends on a source of charge to generate a
change in voltage. The piezoelectric element IS the source of the
voltage.

Post by Jay Ts
Don't expect the piezo transducer to sound exactly that
way. The transducer will give you a sound that is _like_
acoustic, but not the same.

Jenn gave a good description of "quack" for the characteristic of a
piezo guitar pickup, but they actually work fairly well on instruments
that don't have a lot of low end, like the ukulele.

Jay Ts

2008-01-13 19:43:53 UTC

Actually, they put out quite a high voltage - piezo transducers are used
to make a the spark in cigarette and fireplace lighters,

They *can* put out high voltages.

In lighters, the piezo elements are hit by a tiny spring-loaded
hammer. The force on the crystal is huge, and very sudden.

I think my previous comments need to be clarified (really: corrected).
Years ago I experimented with using piezo transducers in my electric
guitars. I had really good results with that.

But that was on electric, not acoustic, which is what this
thread is supposed to be about. I failed to take into account
that acoustic guitar bodies vibrate a _lot_ more than those
in solid-body electrics. So I assume the problem with 'quack'
is magnified, along with output voltage. My bad.

unlike a magnetic
pickup, the piezo pickup itself is insensitive to magnetic fields.

Yes, exactly. One of the things I liked about using piezo
transducers is that with shielding, they can be very insensitive
to EMF.

The way piezo transducers function is not all that unlike the elements
in capacitor microphones do.

Not really. A piezoelecttric transducer generates a voltage when it's
deformed. A condenser mic changes capacitance, which results in a change
in the voltage between two electrically charged plates.

That change in voltage is also caused by a deformation. A
different sort, not using quartz. ;-)

A condenser
microphone depends on a source of charge to generate a change in
voltage. The piezoelectric element IS the source of the voltage.

Yes, that is it. In my mind, the two are a lot more similar
than different, but it depends on how you choose to look at it.

Jenn gave a good description of "quack" for the characteristic of a
piezo guitar pickup, but they actually work fairly well on instruments
that don't have a lot of low end, like the ukulele.

Well, take my above comments into consideration before following
up on this -- when I was experimenting with my electric
guitars, I found I generally got better sound by using smaller
piezo transducers. It might be that the smaller ones pick up
less low frequencies.

Jay Ts

--
To contact me, use this web page:
http://www.jayts.com/contact.php

Mike Rivers

2008-01-13 19:55:05 UTC

Post by Jay Ts

Post by Mike Rivers
Not really. A piezoelecttric transducer generates a voltage when it's
deformed. A condenser mic changes capacitance, which results in a change
in the voltage between two electrically charged plates.

That change in voltage is also caused by a deformation. A
different sort, not using quartz. ;-)

I was trying to be picky here. A condenser mic needs a source of
electrical charge on the plates. The difference in charge between the
plates creates a voltage difference between them. When the capacitance
changes as a result of diaphragm movement, the voltage between the
plates changes.

The charge can be provided by putting a voltage across the plates
through a very high resistance ("externally polarized") or the charge
can be stored in an electret that's part of the capsule construction.
An electret is the the electrostatic equivalent of a permanent magnet.
You don't need an external voltage source to have an electrical
charge.

So a condenser mic always has a voltage across it, and that voltage
changes with motion. A piezoelectric element has no voltage across it
until it's deformed.

Post by Jay Ts
Yes, that is it. In my mind, the two are a lot more similar
than different, but it depends on how you choose to look at it.

I choose to look at it the way it really is. <g>
deration before following

Post by Jay Ts
when I was experimenting with my electric
guitars, I found I generally got better sound by using smaller
piezo transducers. It might be that the smaller ones pick up
less low frequencies.

I've heard of people putting a microphone near the strings of an
electric guitar and adding that to the output of the amplifier or
pickup. So I suppose your experiments with a piezo pickup aren't too
far off that. Leslore has it that Les Paul's first electric guitar was
his acoustic guitar with a phono cartridge attached to it by the
needle. There's a good chance that it was a piezoelectric phono
cartridge.

philicorda

2008-01-16 01:09:16 UTC

On Sat, 12 Jan 2008 14:18:35 +0100, Peter Larsen wrote:

<snip>

Post by Peter Larsen
They ARE non linear by definition. The example is too short to reliably
extract a best guess of its frequency response, but it has a problem at
8117 Hz, try to dip the closest slider on a fairly narrow eq 6 to 12 dB
or de-ess at that exact center frequency, assuming the de-ess frequency
of whatever contraption you have avaiable is adjustable.

More stuff to try. Cheers.

Post by Peter Larsen
And do something about that 50 Hz hum .... possibly indicative of the
piezo needing a buffer amp within inches of wiring instead of furlongs.
Seems to me that it would unavoidably need one anyway to be certain of
having the optimum load.

It would be good to build one Scott Dorsey's DIs into a tiny box that
could be plugged into the socket mounted on the instrument.

Post by Peter Larsen
That Behringer DI, was it active or passive? ... I have a recording of
singer with a grand and then with an electric piano (two consecutive
concerts) coming up, and thinking about getting a couple of their
ULTRA-DI 400P, seems to me that it will offer transformer coupling, and
I like that concept when interfacing with unknown musicians equipment.
Or should I simply mic the unknown piano loudspeaker ... if it was known
good that would be my choice, but with it being undefined I prefer to
keep my options open.

The Behringer DI was the active Ultra-DI D120.
It's fine with line inputs, but I have not got good results with pickups,
whether magnetic or piezo.

Scott Dorsey

2008-01-16 01:44:33 UTC

Post by philicorda
It would be good to build one Scott Dorsey's DIs into a tiny box that
could be plugged into the socket mounted on the instrument.

I built a couple of them dead-bug style, with the parts all mounted
directly on a ceramic piezo element, so the pickup itself was the DI.
It worked pretty well. It's only a small handful of parts.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

John Bennett

2008-01-12 13:20:03 UTC

Post by philicorda
On two separate occasions recently I have recorded ukuleles, and taken
their little piezo pickups as well as a mic.
Both times I had something a bit weird happen.
With my behringer DI they both sounded a bit noisy and lacking in
brightness, but clean. So I plugged them into the DI on my focusrite
ISA200 and there was much less noise, more top end, but they sounded
distorted.
Not in a clipped way, but quite the opposite as though it was just the
low level stuff that was getting distorted.
Here's a clip of the focusrite DI. (1MB 44.1Khz 24bit PCM Wav).
http://www.fast-files.com/getfile.aspx?file=5367
I didn't keep a recording the cleaner noisier behringer DI unfortunately.
So I guess the different impedance had something to do with it, but why
distortion? Do piezo pickups get non linear depending on the load they
are plugged into?

ElectroniX make several neat little buffer/preamp devices to match high
impedance (up to 4.7MegOhm) piezo outputs to lower (10K Ohm) impedance
inputs. (eg: ElectroniX Fm-100 JET Ukulele & Mandolin Buffer Preamp
$29.99.) Using a device like this should make a piezo pickup sound the
same whatever you plug it into (in theory).

They only seem to sell on ebay so check out
http://stores.ebay.com/Music-ElectroniX_W0QQcolZ4QQdirZ1QQfsubZ0QQftidZ2
QQpZ2QQtZkm

Cheers John

--
John Bennett
johna(dot)bennett(at)virgin(dot)net

Jay Ts

2008-01-12 18:30:59 UTC