DIGITAL GUITAR AUTO-TUNER PROJECT

[Jim Thomas]

When you know how things work, the world is
one big sandbox.

Jerry

Ha! Another bit of usenet wisdom for my sig file!

 

[Jerry Avins]

Frnak McKenney wrote:
...

Is there a reason that "tuning instruments" (at least, the ones
I've seen and the ones discussed here) only analyze sounds and don't
attempt to apply controlled signal stimulation? Or is it that such
already exist and are simply too expensive for everyday use?

My guess: generating the sound is usually something that comes so easily
to a musician that it's not worth automating. Something was published on
a piano tuning device that both excited the string -- I forget how --
and turned the tuning peg with a geared servo motor. A human had to
place the string-isolating wedges and move the servo from peg to peg.

Jerry

P.S. Is your name really Frank?

 

[Rich Grise]

When the hammer strikes the strings, they are all in phase, going
up and down (presuming a grand piano with horizontal strings)
together, and passing a lot of energy to the bridge (which goes up and
down with the strings, and transferring this motion to the air),
resulting in much energy being taken from the strings and a high decay
rate. But due to the coupling at the bridge, one or two of the three
strings will eventually change phase until one is going up while the
other(s) are going down. At this point, much less energy (in relation
to the amplitude of each string vibration) is transferred to the
bridge (when one string goes up, its effect on the bridge is mostly
canceled by the other string(s) going down, so the bridge moves up and
down a lot less in relation to string motion), and since less energy
is being taken out of the strings at the bridge, their decay rate is
much longer.

You can demonstrate this energy transfer with a really fun demo:
Take three pieces of string, two weights (maybe a large hex nut, or
fishing weight) - suspend one string horizontally, like in a door
frame, or between two chairs. Make pendulums out of the other two
pieces of string and weights, both the same length, and tie them at
about 1/3 and 2/3 length on the horizontal string:

X---------+-----------+----------X X = support, + = knot
| |
| | - = horizontal string
| | | = vertical string
| |
O O O = pendulum bob

Start _just one_ of these pendulums (pendula?) swinging, and
watch what happens. See also
http://www.tki.org.nz/r/science/scienceschool/resources/physical/swingtime_e.htm
Activity 2.

Cheers!
Rich

 

[Jerry Avins]

Ha! Another bit of usenet wisdom for my sig file!

I wish I had thought of that! (You're welcome.)

Jerry

 

[Jerry Avins]

John Woodgate wrote:

...

If one or both of the outer strings shifts phase, in such a way that the
bridge can twist, the decay is different from the case where the middle
string shifts (relatively).

Can a piano bridge really twist? One is a long strip glued to the sound
board, the other is part of the cast-iron frame. It astonishes me that
twist has a significant affect.

Jerry

 

[John Woodgate]

Can a piano bridge really twist? One is a long strip glued to the sound
board, the other is part of the cast-iron frame. It astonishes me that
twist has a significant affect.

I don't know if it's significant. The sound board bends in all sorts of
ways, so the bridge might be moved by notes other than the one under
consideration.

 

[Jonathan Westhues]

My guess: generating the sound is usually something that comes so easily
to a musician that it's not worth automating. Something was published on
a piano tuning device that both excited the string -- I forget how --
and turned the tuning peg with a geared servo motor. A human had to
place the string-isolating wedges and move the servo from peg to peg.

I read something about a self-tuning piano. It used a magnetic pickup (as
for an electric guitar) to sense the frequency. Presumably they excite the
string the same way, by driving a current through the pickup coil.

I think that was the piano where all the strings were tuned sharp and to
tune a string a current was allowed to flow through the string, heating,
lengthening and flattening it. If they used a pickup instead of a microphone
then they could tune multiple strings at once without them bleeding into
each other. Very clever.

Jonathan
http://cq.cx/

 

[Jon Harris]

Frnak McKenney wrote:
...


My guess: generating the sound is usually something that comes so easily
to a musician that it's not worth automating. Something was published on
a piano tuning device that both excited the string -- I forget how --
and turned the tuning peg with a geared servo motor. A human had to
place the string-isolating wedges and move the servo from peg to peg.

Maybe it would make sense for something like piano, but consider that guitar
tuners cost about 20 bucks and can fit in a back pocket. Adding some for
stimulation is going to be pretty expensive compared to that, plus as Jerry
said, musicians are pretty good at plucking their own strings! Plus, I don't
many people that would trust a machine "banging on" their expensive instruments.

Jerry

P.S. Is your name really Frank?

I was wondering the same thing.

 

[Jerry Avins]

Maybe it would make sense for something like piano, but consider that guitar
tuners cost about 20 bucks and can fit in a back pocket. Adding some for
stimulation is going to be pretty expensive compared to that, plus as Jerry
said, musicians are pretty good at plucking their own strings! Plus, I don't
many people that would trust a machine "banging on" their expensive instruments.




I was wondering the same thing.

Somewhere in the attic, I have an oak box with a tuning fork mounted on
it. One tine of the fork is driven by a coil and the other drives the
button of a diaphragmless carbon microphone that modulates the coil
current. Coil voltage is available on binding posts. At one time, it was
General Radio's premier 1 KHz frequency standard. Feeding back to a
mechanical resonator has been done for a long time.

Jerry

 

[Tony]

Maybe it would make sense for something like piano, but consider that guitar
tuners cost about 20 bucks and can fit in a back pocket. Adding some for
stimulation is going to be pretty expensive compared to that, plus as Jerry
said, musicians are pretty good at plucking their own strings! Plus, I don't
many people that would trust a machine "banging on" their expensive instruments.


I was wondering the same thing.

A guitar already has a mag pickup, so it should be possible to just
plug it into a tuner (with vol and tone right up) and have the tuner
search for the slight narrow-band impedance resonances at each string
pitch, then use that to sustain continuous oscillation. Of course it
would probably also pick up harmonics of other strings if they weren't
damped (ideally need access to a hex pickup as well, I guess). A
practical design would be tricky, but still quite cheap.

Tony (remove the "_" to reply by email)

 

[David Tweed]

That is, why not have the "tuning instrument" induce the vibration
as well as analyze the resulting sound.

Because the whole point is to get the instrument in tune *as played*
by the performer. It is a good thing that the tuning analysis is as
passive as possible.

A surprising number of musicians, as well as nonmusicians don't seem
to get this: An instrument that's in "perfect tune" can be played
out of tune by a bad player (or deliberately by a good player), and
a badly-tuned instrument can be played in-tune by a good player. The
quality of the overall performance depends a lot more on the player
than on the instrument.

I happen to play trombone, which is an extreme example of this, but
it applies to all wind instruments and most stringed instruments.
A piano (and electronic synthesizer), which I also play, is at the
other extreme, being one of the instruments on which the performer
has almost no real-time control over the pitch.

-- Dave Tweed

 

[John Woodgate]

I happen to play trombone, which is an extreme example of this,

My colleague, John Bowsher (a physicist as well as a trombonist)
demonstrated this to an AES British Section meeting many years ago. Two
demos:

- producing a constant pitch note while collapsing the slide.

- producing a swept pitch note with the slide stationary.

I don't really believe it, and I was there!

 

[Bob Stephens]

On Fri, 29 Apr 2005 13:36:23 GMT, David Tweed wrote:

I happen to play trombone, which is an extreme example of this, but
it applies to all wind instruments and most stringed instruments.
A piano (and electronic synthesizer), which I also play, is at the
other extreme, being one of the instruments on which the performer
has almost no real-time control over the pitch.

-- Dave Tweed

I's have to disagree on the synthesizer. With pitch benders, modulation
wheels, breath controllers, etc... the performer has at least as much
control over pitch as a tromboner. Leads to some gawd-awful playing too.


Bob

 

[Frnak McKenney]

Frnak McKenney wrote:
...


My guess: generating the sound is usually something that comes so easily
to a musician that it's not worth automating. Something was published on
a piano tuning device that both excited the string -- I forget how --
and turned the tuning peg with a geared servo motor. A human had to
place the string-isolating wedges and move the servo from peg to peg.

Ah. Sounds reasonable. I wasn't thinking of making the entire
process automated, but you've given me another obstacle to consider

P.S. Is your name really Frank?

Yes, my fingers are just a little dylsexic. I'm in an odd industry
for someone who was finally permitted to drop Typing in the 7th
grade, and (aside from 026/029s) my first real computer keyboard
experience was with something called APL with a very "different"
keyboard layout. <grin>


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
Everything has to start with fantasy... Knowledge is what
you finish up with, if you're lucky, after you've done the
hard work -- but the hard work needs passion to drive it.
People need reasons to be interested, reasons to be committed,
reasons to do their damndest to find the truth.
-- Brian Stableford / Dark Ararat
--

 

[Frnak McKenney]

I was wondering the same thing.

I've typed it that way often enough for me to consider legally changing it,
but it's in the header mainly as one more obstacle in the way of address
harvesting programs.


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)

 

[Kelly Hall]

An instrument that's in "perfect tune" can be played
out of tune by a bad player (or deliberately by a good player), and
a badly-tuned instrument can be played in-tune by a good player.

A trombone will be played out-of-tune by a bad player and will not be
touched by a good player. Same thing for the soprano sax and oboe.

In all seriousness, I would much rather play trombone than trumpet (my
two main axes) in a large ensemble because it's so much easier for me to
adjust the pitch while I play.

Kely

 

[Frnak McKenney]

Because the whole point is to get the instrument in tune *as played*
by the performer. It is a good thing that the tuning analysis is as
passive as possible.

The nice thing about a microprocessor-controlled tuner is that it
can be configured to match multiple "good" settings... assuming
these can be defined in a way so they can be recognized.

A surprising number of musicians, as well as nonmusicians don't seem
to get this: An instrument that's in "perfect tune" can be played
out of tune by a bad player (or deliberately by a good player), and
a badly-tuned instrument can be played in-tune by a good player. The
quality of the overall performance depends a lot more on the player
than on the instrument.

I happen to play trombone, which is an extreme example of this, but
it applies to all wind instruments and most stringed instruments.
A piano (and electronic synthesizer), which I also play, is at the
other extreme, being one of the instruments on which the performer
has almost no real-time control over the pitch.

Fair enough, I can see how a violin's "tuning" can be tweaked by
minor adjustments of the fingers, and a trombone is also offers a
continuous frequency spectrum. Not sure if that makes a self-
stimulating tuner _useless_ -- it just says that it's probably not a
useful approach for some (perhaps many) instruments.

Ignoring the electronic synthesizer (I just ran across a couple of
hex-shafted ferrite-slug-coil tuning wands <grin>), which
instruments might benefit? Guitar&fretted, piano&friends... drums?
I have _no_ idea how (or if) one tunes a xylophone...

I admit that my interest is a combination of a life as a consultant
("Wait a minute! I can make that much MUCH better!") as well as
several frustrating years trying to tune a guitar to match a tin ear
(my own). So far, my picture of this thing is a slim wand with a
microphone, a string of LEDs (TooLow...TooHigh) and a pager motor
with a hard-rubber- coated cam, but I admit I'm probably not going
to build it _this_ week. <grin>


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)

 

[Jon Harris]

A guitar already has a mag pickup, so it should be possible to just
plug it into a tuner (with vol and tone right up) and have the tuner
search for the slight narrow-band impedance resonances at each string
pitch, then use that to sustain continuous oscillation. Of course it
would probably also pick up harmonics of other strings if they weren't
damped (ideally need access to a hex pickup as well, I guess). A
practical design would be tricky, but still quite cheap.

I assume you are talking about using the pickup in reverse, i.e. to drive the
strings to vibrate? Well, it's true that _some_ guitars have passive magnetic
pickups. But others have different types including active pickups. With active
pickups, you can't just reverse drive them from the 1/4" input--the output
buffer gets in the way.

 

[Rich Grise]

I've heard of those "self-tuning" pianos, and from what I've heard,
hearing it tune itself is almost a transcendental auditory experience. %-}

Somewhere in the attic, I have an oak box with a tuning fork mounted on
it. One tine of the fork is driven by a coil and the other drives the
button of a diaphragmless carbon microphone that modulates the coil
current. Coil voltage is available on binding posts. At one time, it was
General Radio's premier 1 KHz frequency standard. Feeding back to a
mechanical resonator has been done for a long time.

World's first "Accutron"!

Cheers!
Rich

 

[Rich Grise]

On Thu, 28 Apr 2005 14:58:04 -0700, "Jon Harris"

A guitar already has a mag pickup, so it should be possible to just plug
it into a tuner (with vol and tone right up) and have the tuner search
for the slight narrow-band impedance resonances at each string pitch,
then use that to sustain continuous oscillation. Of course it would
probably also pick up harmonics of other strings if they weren't damped
(ideally need access to a hex pickup as well, I guess). A practical
design would be tricky, but still quite cheap.

Electric guitarists have been doing this acoustically since they
discovered feedback. I guess there's a whole mystique (sp?) about
the process - I think they toss the term "sustain" about. (my brugly
other is a professional guitarist, on the side.)

Cheers!
Rich