magnetic field

[H. Dziardziel]

On Wed, 27 Apr 2005 07:37:40 GMT, "CWatters"
<colin.watters@pandoraBOX.be> wrote:

deepaa@gmail.com> wrote in message
news:1114565054.117886.45800@g14g2000cwa.googlegroups.com...
Wondering if I need to buy a NiMH charger for NiMH rechargeable AA
batteries or a normal AA charger will work with the NiMH batteries. Can
anyone tell me if this is possible?

If it claims to be a fast charger for NiCad cells then it's not a good idea
to use it with NiMH cells. If it's designed to trickle charge cells
overnight then it might work ok.

If your house burns down it's your fault though.

Please note charging overnight isn't "trickle" charging.
Overnight is standard C/10 charging (for the original charger
design cell capacity) although sometimes it can be as high as C/5.

NiMh shouldn't be (true) trickle charged (<C/20) in any case.
They may be never be charged fully or conversely depending on
the charge and cells, overcharged and lose capacity.

 

[Ben Bradley]

On Mon, 25 Apr 2005 15:43:53 -0400, Jerry Avins <jya@ieee.org> wrote:

Robert Scott wrote:
On Mon, 25 Apr 2005 11:18:06 -0400, Jerry Avins <jya@ieee.org> wrote:

Re: inharmonicity in strings:


I know that you are right, but it puzzles me. It seems to me that the
common bridge should enforce harmonicity, just as it locks together the
slightly detuned piano doubles and triplets. (Exact tuning makes the
note loud ans it's decay rapid. Slight detuning softens the attack,
hoarding energy for better sustain. The same is true of a 12-string guitar.)

...

Yes, there is in fact a "lock-in" phenomenon that happens through the
interaction at the bridge. But typical amounts of inharmonicity, at
least in piano strings, exceeds the lock-in range. Inharmonicity is
easily measured by precisely measuring the pitch of individual
overtones and comparing them. Another way to verify inharmonicity is
to observe the signal on a scope. If the overtones were all locked to
the fundamental, the overall shape of the signal would be constant,
just decaying in amplitude. Perhaps the individual overtones would
decay at different rates. But it would be quite clear that the
overtones are frequency locked. But that is not in fact what you will
observe. If the scope is triggered by the fundamental, then the
overtones will appear as higher-frequency components that are "riding
to the left" as compared to the fundamental.

I agree. One point of quibble: even if the overtones were frequency
locked, the wave shape would still change with time. Different overtones
have different decay rates.

Lower harmonics may well be locked together through the bridge
interaction, though I believe that with increasing harmonic number
there is less coupling at the bridge, the most coupling being at the
fundamental.
But there's another phenomenon in the piano having nothing to do
with harmonics when several strings are sounded in unison, and this
causes tje result described above, "Exact tuning makes the note loud
ans it's [and its] decay rapid" and you would presumably see this in
the amplitude on the oscilloscope, especially if you were looking for
a perfect exponential decay of amplitude, and wonder what's going on.
The decay will be quite fast in the first few seconds, then much
slower in the seconds thereafter.
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.
This is a part of the piano's sound (fast decay at the start of the
note, slow decay after a few seconds) that cannot be made with a
single-string-per-course instrument. I intentionally ignored the
harmonics in the above description to simplify things, but the
harmonics might also change phase in the same or a similar way.
There have been three or four articles on the piano in Scientific
American over the past 30 or 40 years, and I recall reading the above
description of the string changing phase in one of them.

Jerry

-----
http://mindspring.com/~benbradley

 

[keith]

On Wed, 27 Apr 2005 15:28:27 +1200, Ken Taylor wrote:

"keith" <krw@att.bizzzz> wrote in message
newsan.2005.04.27.02.16.24.179681@att.bizzzz...
On Tue, 26 Apr 2005 11:47:24 -0500, Richard Owlett wrote:

John Woodgate wrote:

I read in sci.electronics.design that Jerry Avins <jya@ieee.org> wrote
(in <X6WdncXj2cQk__DfRVn-sA@rcn.net&gt about 'DIGITAL GUITAR AUTO-TUNER
PROJECT', on Mon, 25 Apr 2005:

So what if there were? Anyway, with all the cross posting, there bound
to be some groups whose charters touch on every part, but probably
none that touch on all.


An ichthyology group should be added, so that tuna experts can
participate.

That sounds fishy.

How many newts in the scale?

--
Keith

How many scales on a newt?

The converse of a statement proves nothing. ;-)

--
Keith

 

[Ben Bradley]

Just scroll down, folks, cause I don't top-post...

In sci.electronics.design,sci.electronics.misc, On Mon, 25 Apr 2005
17:34:09 GMT, Al Clark <dsp@danvillesignal.com> wrote:

no-one@dont-mail-me.com (Robert Scott) wrote in news:426ce85a.8724019
@news.provide.net:


...

This phenomenon has been well-studied for pianos where precise tuning
is much more important. It is called "inharmonicity", and it is due
to the stiffness of the strings. The overtones are theoretically pure
harmonics only for an infinitely thin string with zero stiffness,
where the restoring force is totally due to the tension in the string.
When part of the restoring is force is due to stiffness in addition to
tension, then higher overtones will be higher in pitch than pure
multiples because higher overtones involve more bending than lower
overtones. A typical overtone series might be:

1.000 (fundamental)
2.003 (second partial)
3.008 (third partial)
4.015 (fourth partial)
5.024 (fifth partial)
6.035 (sixth partial)
...etc.

The effect may be less on guitars than on pianos because the length to
thickness ratio is not as bad on a guitar. But it is still enough of
an effect to be considered in the design of a tuner.


-Robert Scott
Ypsilanti, Michigan

I observed this many years ago using an FFT analyzer. As I recall (25
years ago),I also noticed that the G string on my guitar was actually
vibrating at two different frequencies that straddled the desired center.
I think this is why I never think that a B created at the 4th fret of the
G string ever sounds perfectly in tune with the B string. I attributed
this to the fact that the G is a wirewound string and therefore has
significant thickness.

Have you tried this several times, with different guitars, or with
the same guitar after changing strings? The fact that G is wirewound
may have its effect, but there are other things. If the string does
not have a very consistent weight along its length, perhaps one end is
slightly thicker and heavier than toward the other (whether from wear,
dirt accumulation, or faulty manufacture), the harmonics will be out
of tune with the fundamental (or much moreso than with a 'good'
string), and fretted notes are going to be sharper or flatter in
relation to the open string than they will be for a consistent string.
Imperfect strings are one thing that has driven me crazy (and I'm sure
many other guitarists) before I figured it out. I read about "turning
around the string" on a classical guitar in an attempt to get better
intonation from it in Jose Oribe's book "The Fine Guitar" (I see it's
now out of print, get a used copy before the price goes up any
further).

As was mentioned earlier, the choice of temperment is always a
compromise. The frets contribute to temperment as well, I wonder what the
best compromise tuning is for a guitar given all the various parameters.

You might start with the fact that a guitar is usually tuned E A D G B E.

I suppose a smart tuner could have open tuning capabity as well. Open
tunings might be easier to consider if you want fifths and thirds etc to
be perfect (1.5 vs 1.4983 & 1.25 vs 1.25992)

You can tune for a particular key, but it makes things sound worse
for different keys, or even some chords IN that key.

Piano tuners fight the temperment issue all the time. If I have a piano
tuner come out and tune my piano to even temperment (unfortunately, the
typical situation), I hate the sound. I used to have a guy who tuned most
of the pianos for the recording studios in my area tune my piano. When he
did the tuning, my piano sung!

A piano is either tuned for equal temperament (I think virtually
all of them are), or it only sounds good in some keys. I suspect both
tuners aimed for and perhaps got equal temperment, but the second one
knows more about how much to stretch-tune each instrument - the higher
notes are tuned slightly sharp, and the lower ones are tuned slightly
flat, relative to the middle octave. This is done so the higher notes
are 'in tune' with the slightly-sharp harmonics of the lower notes.
I've seen on the Web different tables of just how much to stretch-tune
each of the notes on different models of pianos.

Too bad I can't actually play very well.....

Unfortunately (fortunuately) I have a pretty good sense of pitch.

I do to, and it used to frustrate me as to why my guitars were out
of tune and wouldn't tune right. Now I KNOW why. Actually, with
some work and the proper tools (g-tune is a nice precision tuner for
adjusting guitar harmonics (nut as well as bridge positioning) and
general tuning) I've been getting things under control.


-----
http://mindspring.com/~benbradley

 

[Jerry Avins]

keith wrote:

...

The converse of a statement proves nothing. ;-)

Oh? I thought it proved the converse.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[Jerry Avins]

Ben Bradley wrote:

On Mon, 25 Apr 2005 15:43:53 -0400, Jerry Avins <jya@ieee.org> wrote:


Robert Scott wrote:

On Mon, 25 Apr 2005 11:18:06 -0400, Jerry Avins <jya@ieee.org> wrote:

Re: inharmonicity in strings:



I know that you are right, but it puzzles me. It seems to me that the
common bridge should enforce harmonicity, just as it locks together the
slightly detuned piano doubles and triplets. (Exact tuning makes the
note loud ans it's decay rapid. Slight detuning softens the attack,
hoarding energy for better sustain. The same is true of a 12-string guitar.)


...


Yes, there is in fact a "lock-in" phenomenon that happens through the
interaction at the bridge. But typical amounts of inharmonicity, at
least in piano strings, exceeds the lock-in range. Inharmonicity is
easily measured by precisely measuring the pitch of individual
overtones and comparing them. Another way to verify inharmonicity is
to observe the signal on a scope. If the overtones were all locked to
the fundamental, the overall shape of the signal would be constant,
just decaying in amplitude. Perhaps the individual overtones would
decay at different rates. But it would be quite clear that the
overtones are frequency locked. But that is not in fact what you will
observe. If the scope is triggered by the fundamental, then the
overtones will appear as higher-frequency components that are "riding
to the left" as compared to the fundamental.

I agree. One point of quibble: even if the overtones were frequency
locked, the wave shape would still change with time. Different overtones
have different decay rates.


Lower harmonics may well be locked together through the bridge
interaction, though I believe that with increasing harmonic number
there is less coupling at the bridge, the most coupling being at the
fundamental.
But there's another phenomenon in the piano having nothing to do
with harmonics when several strings are sounded in unison, and this
causes tje result described above, "Exact tuning makes the note loud
ans it's [and its] decay rapid" and you would presumably see this in
the amplitude on the oscilloscope, especially if you were looking for
a perfect exponential decay of amplitude, and wonder what's going on.
The decay will be quite fast in the first few seconds, then much
slower in the seconds thereafter.
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.
This is a part of the piano's sound (fast decay at the start of the
note, slow decay after a few seconds) that cannot be made with a
single-string-per-course instrument. I intentionally ignored the
harmonics in the above description to simplify things, but the
harmonics might also change phase in the same or a similar way.
There have been three or four articles on the piano in Scientific
American over the past 30 or 40 years, and I recall reading the above
description of the string changing phase in one of them.

That's a good description that I omitted for brevity. You did a better
job of describing it than I would have. The math, at least for two
strings, is relatively simple. It is in many texts on diff-eq for
engineers and physics lab demos as the "coupled pendulum" demonstration.
Tuning the strings so that they just barely lock in frequency gives the
longest sustain. If they slip just a bit further apart than that, the
typical way-out-of-tune twang is the result. Just a touch with a
quarter-inch-drive socket face up and turned with an Allen wrench can
restore the lock. When three strings are involved, it is usually easy to
identify the one that slipped. With two, even if you tweak the wrong
string and so leave the note out of tune, it sounds so much better that
you'll get laurels anyway. When you know how things work, the world is
one big sandbox.

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[keith]

On Mon, 25 Apr 2005 09:07:14 -0400, Keith Williams wrote:

In article <23be6f4c.0504220601.6f4a75ef@posting.google.com>,
dhaevhid@hotmail.com says...
hi! im a total newbie on the field of assembly programming and the
microcontrollers stuff and im trying to build a digital guitar tuner
more like the ones which automatically detects the string being tuned
and has an LCD "analog needle-display"... any kind of help would be
greatly appreciated.. sample codes, ideas, references, anything would
be great..

I've read (most of) the answers here and they've gone for the first
things I'd try, so it's out-of-the-box time [*]. What about an optical
interrupter (or reflection) at the center (maxima) of the string
feeding a microcontroller's timer?

Ok, so my optical idea wasn't taken well. What about dopler radar? I
remember when police radars were calibrated using tuning forks.

Yeah, microphones are just too obvious. ;-)

--
Keith

 

[keith]

On Wed, 27 Apr 2005 22:08:59 -0400, Jerry Avins wrote:

keith wrote:

...

The converse of a statement proves nothing. ;-)

Oh? I thought it proved the converse.

No, I think you'll find that it does _not_ prove the converse. ;-)

--
Keith

 

[Jerry Avins]

keith wrote:

On Wed, 27 Apr 2005 22:08:59 -0400, Jerry Avins wrote:


keith wrote:

...


The converse of a statement proves nothing. ;-)

Oh? I thought it proved the converse.


No, I think you'll find that it does _not_ prove the converse. ;-)

You mean that proving the converse doesn't prove anything? Oh, I get it!

The converse of something is nothing.

Proving the converse of something proves nothing.

Ah, so!

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[John Woodgate]

I read in sci.electronics.design that Ben Bradley
<ben_nospam_bradley@frontiernet.net> wrote (in
<esc0711h1nrvtt6t8gvmvh7t7o5fbrcfn9@4ax.com&gt about 'DIGITAL GUITAR
AUTO-TUNER PROJECT', on Thu, 28 Apr 2005:

There have been three or four articles on the piano in Scientific
American over the past 30 or 40 years, and I recall reading the above
description of the string changing phase in one of them.

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).
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Frnak McKenney]

Followup-To:

On Wed, 27 Apr 2005 21:33:39 -0400, keith <krw@att.bizzzz> wrote:

On Wed, 27 Apr 2005 15:28:27 +1200, Ken Taylor wrote:
"keith" <krw@att.bizzzz> wrote in message
newsan.2005.04.27.02.16.24.179681@att.bizzzz...
On Tue, 26 Apr 2005 11:47:24 -0500, Richard Owlett wrote:
John Woodgate wrote:
An ichthyology group should be added, so that tuna experts can
participate.

That sounds fishy.

How many newts in the scale?

How many scales on a newt?

The converse of a statement proves nothing. ;-)

And now for something completely off-the-scale:

While I'm barely at the "hacker" stage in my DSP knowledge (I'm
still working out how modulating a reflected mm-wavelength signal can
yield accurate distance measurement over thousands of mm), I have
been following the threads in this Subject-line with great interest.

I'm particularly fascinated with the complexity of obtaining a
"useful" or "pleasing" tuning for a musical instrument. I hadn't
realized that there were multiple "standard" ways of tuning a piano,
for example. Thank you all for giving me an excuse to renew my
Usenet Lurker's License. <grin>

I'd like to ask one question, though, regarding the tuning process
for instruments involving mechanical vibration -- not just the ones
someone referred to as "plucked" but also percussion instruments and
probably others. If, as some have mentioned, the tuning of stringed
instruments is made more difficult because people pluck the strings
differently (is this the same as "attack". or is that a "keyboard
only" term?) and the sound changes over time (decay), why not add a
feedback loop into the process?

That is, why not have the "tuning instrument" induce the vibration
as well as analyze the resulting sound. A PWM-speed-controlled
motor with a _gentle_ off-center cam is probably not the only
approach. but it doesn't seem very difficult to do (certainly no
more difficult than analyzing the pure sine wave coming from a
guitar string <grin&gt.

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?


(Whoops! I think I just violated my ULL! Time to re-cloak... er,
re-Lurk. <grin&gt

Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
"Very few things happen at the right time, and the rest
do not happen at all. The conscientious historian will
correct these defects." -- Herodotus
--

 

[Jim Thomas]

Jerry Avins wrote:

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

Jerry

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

--
Jim Thomas Principal Applications Engineer Bittware, Inc
jthomas@bittware.com http://www.bittware.com (603) 226-0404 x536
When you know how things work, the world is one big sandbox. - Avins

 

[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?
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[CWatters]

<cswanson2@austin.rr.com> wrote in message
news:1114660367.778602.101320@l41g2000cwc.googlegroups.com...

I need to power a water valve actuator with 24AC 650 mA. I cannot
easily find a 650mA 24VAC supply, but 1amp or 2amp or so I can find.

Either should work fine.

The current rating of a power supply is usually a maximium rating that the
load must not exceed. eg the 1A model can supply 24VAC at upto 1A. The load
only requires 0.65A so it's ok.

 

[Rich Grise]

On Thu, 28 Apr 2005 01:27:43 +0000, Ben Bradley wrote:

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]

Jim Thomas wrote:

Jerry Avins wrote:

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

Jerry


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

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

Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[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
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ

 

[John Woodgate]

I read in sci.electronics.design that Jerry Avins <jya@ieee.org> wrote
(in <1Nmdnfkcs6hKkOzfRVn-qQ@rcn.net&gt about 'DIGITAL GUITAR AUTO-TUNER
PROJECT', on Thu, 28 Apr 2005:

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.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jonathan Westhues]

"Jerry Avins" <jya@ieee.org> wrote in message
news:2LKdndtBrcfiZO3fRVn-pA@rcn.net...

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]

"Jerry Avins" <jya@ieee.org> wrote in message
news:2LKdndtBrcfiZO3fRVn-pA@rcn.net...

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.

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.