DIGITAL GUITAR AUTO-TUNER PROJECT

[John Woodgate]

Winding adds far more mass than stiffness, making the string more
harmonic. Some materials are better than others. Fine silver is used
for violins and cellos. Gold is be better.

Why would gold be better? If it's density, depleted uranium should be
even better!

 

[Spehro Pefhany]

Why would gold be better? If it's density, depleted uranium should be
even better!

The numbers I saw last time I looked at were only an RCH apart at
~19.3 gm/cm^3 (along with tungsten). Osmium, rhenium, iridium and
platinum are a fair bit higher; plutonium a bit higher.

http://www.science.co.il/PTelements.asp


Best regards,
Spehro Pefhany

 

[Bob Monsen]

A piano's "stretch" over its 7.5 octaves is the better part of a
semitone. By attaching discrete weights to the strings, most of the
inharmonicity can be removed. (The windings on the low strings end well
short of the bridges, reducing inharmonicity of the second partial.) A
piano so doctored is tuned without stretch. It sounds awful!

Jerry

That is interesting. The book I referenced mentioned another possibility
for why the stretch occurs. The human ear has far less ability to
discriminate pitch at low and high frequencies than it does in the
middle range. The other possibility was that the extra bit was required
to overcome this inability, forcing the ear to hear an octave. However,
the text also states that studies by Backus indicate that the mechanism
of string inharmonicity accounts for most of the stretching..

I guess you have listened to these pianos. Do the high strings sound flat?

 

[Bob Monsen]

Mine comes and goes.

I have a friend who claims to have had perfect pitch until her 55th
birthday or thereabouts, at which point her perfect pitch started to go
low (or high, I can't remember which). Anyway, it disturbed her quite a
lot, because it made her favorite recordings seem out of pitch. I guess
it would be like having all your green things suddenly turn yellow. You
might get used to it, but it would be disconcerting.

Regards,
Bob Monsen

 

[Jerry Avins]

It stands for a very great deal, and it's the newsgroup you are
participating in.

Ah! I'm subscribed to comp.dsp. Ain't cross posting fun?

Jerry

 

[Richard Owlett]

It stands for a very great deal, and it's the newsgroup you are
participating in.

Ahh but Jerry(and others)lurk(s) on comp.dsp
The joys of cross posted threads ;}

 

[Jerry Avins]

s.e.d. = sci.electronics.design. I think this was a joke, playing off the word
"temperament". Get it?

I do now. It's a pretty good one for off the cuff, as it were.

Jerry

 

[Jerry Avins]

That is interesting. The book I referenced mentioned another possibility
for why the stretch occurs. The human ear has far less ability to
discriminate pitch at low and high frequencies than it does in the
middle range. The other possibility was that the extra bit was required
to overcome this inability, forcing the ear to hear an octave. However,
the text also states that studies by Backus indicate that the mechanism
of string inharmonicity accounts for most of the stretching..

I guess you have listened to these pianos. Do the high strings sound flat?

Not so much flat as dull. Even single notes. Vladimir Horowitz
disparaged the notion of changing the sound of a piano by the way one
strokes the keys. He said, "There is such a thing as pianistic touch,
but it cannot be demonstrated by playing a single note." Nevertheless,
if we pretend for now that "touch" matters, a piano corrected for
inharmonicity sounds to me as if the pianist were wearing thick felt
gloves. The notes have no ... sparkle? We don't have the words. Have you
ever improved a stew by adding a little vinegar? Inharmonicity is a
piano's vinegar. Hammond organs are harmonic.

Jerry

 

[John Woodgate]

I read in sci.electronics.design that Bob Monsen <[email protected]>

I have a friend who claims to have had perfect pitch until her 55th
birthday or thereabouts, at which point her perfect pitch started to go
low (or high, I can't remember which). Anyway, it disturbed her quite a
lot, because it made her favorite recordings seem out of pitch.

Look for a winding handle at about waist-level. (;-)

 

[[email protected]]

You are incorrect, because you didn't think of the real-world problem
here.

You can't use as many points as you want, for two reasons: the guitar
string signal doesn't last forever... ....
To increase resolution, you have to increase the number of points, hence
the duration of the take.

The number of points used for resolution can be independant of the
duration of the music input signal and the sample rate. See comments
in other comp.dsp threads about FFT interpolation and zero padding.

But don't take my word for it. Just do it.

What makes you think I haven't? Depending on the circumstances (type
of instrument, amount and type of background noise, microphone
characteristics, cpu power available, preferred user interface, etc.)
and metrics (cents accuracy, response time, etc.), methods using FFTs
as part of an algorithm can be either better or worse than the method
you describe later on in this thread.

 

[Jerry Avins]

Ville Voipio wrote:

...

The idea of fixed frets is
a new one, older instruments tend to have movable frets.
My viol (viola da gamba) has tied frets, and I really have
to move them depending on the temperament. Actually, the
deviation from even temperament is very visible (some
frets are closer to each other than others). And talking about
bending... some of the frets are actually non-horizontal
to give better temperament.

Classical guitars have a tilted bridge (bridge compensation), so in
effect, all its frets are non horizontal.

[fine discourse snipped]

(I just wonder if there was anything not off-topic in this posting?)

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.

Jerry

 

[Jerry Avins]

Ville Voipio wrote:

...

The tuner is quite fine with violins, flutes, and even piccolo flutes,
but not very good with cellos, double basses, bass viols or other
low instruments. It does find the correct note, but the detection
is then very sensitive to higher-frequency noise.

That seems to suggest that good performance depends in part on a
low-pass filter, and that the cut-off is higher than optimum for low
instruments. That also suggests that an improved model might have a
variable filter or a choice of fixed ones. It tales longer to count
cycles in low notes, but I think that effect must be secondary.

...

Jerry

 

[[email protected]]

The Fourier analysis assumes that you have a constant amplitude
_repeatable_ waveform, unfortunately a string instrument does not
generate such signals, so you have to analyze some part after the
initial transient.

An FFT is only a transform from one set of basis vectors to another.
One need not make any assumptions about what happens outside the
FFT sample window, particularly the assumption that the waveform
will repeat when it doesn't. And there are several windowing
methods to help deal with any transient artifacts which might be
related to the ends of any data sample window.

 

[Bob Monsen]

Hammond organs are harmonic.

That describes it quite well.

 

[[email protected]]

If a correctly done FT fails to deliver the necessary frequency
resolution on the given data, then no other technique is going to
work. The fundamental problem is not the FT, it's the data: the
frequencies found in a given data sample are *undefined* beyond a
certain accuracy.

Alas, the stated problem is different from that of just using the
mathematical
definition of frequency given an FT; it's more about whether and how
humans
would *perceive* a pitch, and, if so, whether it's sharp or flat. An
FFT is
just one of several computationally efficient mechanisms to help with
estimating
the results of a human ear-brain response, given the current lack of a
complete
and accurate model of this system.


IMHO. YMMV.

 

[Al Clark]

Even though I have no idea what s.e.d. stands for, I doubt you can
implement selectable intonation without getting into the firmware. In a
YDP-233, one can chose among equal temperament (the default), or pure
major, pure minor, Pythagorean, mean tone, Werkmeister, and Kirnberger,
all with any base note. You can also transpose any number of half tones
and pull the pitch of A440 in about .2 Hz increments from 427 to 453. It
doesn't sound like the Steinway it replaced (my daughter has that now),
but it's fun to play with as well as on. It will record two tracks and
has a MIDI interface. More than I need.

Jerry

Sounds like fun! but I'd take the Steinway.

Al

 

[dhaevhid]

Somebody called me that once, and I thought it was rather cute, so
started using it, for the times that I'm consciously being a wacko.

As to who's the asshole, ISTR responding to a "please do this for me"
type of post, and I made a casual offer to do the work, for a price.
Lessee...

Oh, yeah. Here it is:
----excerpt----
From: [email protected] (dhaevhid)
...
its actually a qualifying sample project for my first job.
...
im tryin to do it all by myself but its taking me so long to understand
the concepts...
----end excerpt---

So, in other words, you're not qualified for the job, so you want
us to help you cheat your way in. _That's_ what the asshole part
was for.
--
Cheers!
Rich
------
"There was an old man of Tagore
Whose tool was a yard long or more,
So he wore the damn thing
In a surgical sling
To keep it from wiping the floor."

THERE HAVE BEEN A LITTLE LESS THAN A HUNDRED REPLIES ON THIS THREAD
BUT UNDOUBTLY, IT TOTALLY CLEAR THAT YOU'RE THE ONLY ASSHOLE HANGING
AROUND WITH SERIOUS THINKERS. IF IT SO HAPPENED THAT ALL OF THE OTHERS
RESPONDED THE WAY YOU DID, MAYBE I WOULD THINK I WAS BEING AN ASSHOLE.

GUESS WHAT? YOU'RE THE SOLE STINKING SHIT SURROUNDED BY DECENT
INTELLIGENT PEOPLE.

IM GETTING THINGS QUITE FAST NOW AND I CAN SAY THAT I CAN FINISH THE
PROJECT ON TIME. THANKS FOR ALL THE GREAT MINDS WHO SHARED THEIR VIEWS
AND EXPERTISE. SO IM KEEPING MY JOB, IM GETTING A LOT MORE LEARNING
THAN EVER BEFORE AND I FOUND NEW GREAT FRIENDS ALL OVER THE WORLD.

AS FOR YOU, SAY SORRY TO YOUR MOTHER BECAUSE YOU JUST PROVED THAT SHE
DEFINITELY FAILED TO RAISE YOU WELL...

 

[John Woodgate]

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.

 

[Tony]

I'd be interested to read that article - can you recall the issue, or
even the year?

Most of them use a simple design. You can find one on CircuitCellar,
and that's pretty much how this is done in commercial products.

It consists of an input stage, which is basically a good low-pass filter
filtering everything above the maximum fundamental frequency it's
supposed to deal with (probably something like 1000 or 1500 Hz), usually
a 2nd order active filter. Then it's followed by a comparator set with
some hysteresis, which can also be an amplifier based on some AOP with
a lot of gain - so that the AOP clips the signal, which is easily
transformed into a digital signal with a schmitt trigger, for instance.
This circuit basically extracts the fundamental frequency of the input
signal with a reasonable usability.

Then the comparator's output can be dealt with in various ways.
Some can be rather crude (just measuring the frequency of the resulting
digital signal), some are more clever, and I like the one that's used
in the CircuitCellar project. The comparator's output goes to a digital
I/O pin of a microcontroller, of course set as an input. The algorithm
used consists of measuring the delay between two consecutive raising
edges - but this is not all. To make sure the measure is meaningful,
several consecutive measures are compared, and only if we get a few
(like 10, for instance) consecutive measures that are close enough
to one another, do we consider this is the fundamental frequency.
The latter is computed from the period, using for instance an average of
the 10 given "meaningful" past measures.

By comparing the frequency with a few preset ranges, the tuner can
even guess what the string it is you're trying to tune, and
automatically give you how far away you are from the nominal
frequency for this string.

As to how the above input stage, based on a filter and a saturation
stage, translates in the frequency domain (in other words, how
the spectrum of the original signal is transformed), I'll let you
think about it. It resembles, but is not quite like simply looking
at zero-crossings - because the saturation on the signal actually
tends to "ignore" the harmonics, whereas simple zero-crossing
analysis has to deal with them.

All in all, this is a working approach and it's much simpler than any
sophisticated DSP analysis you might try.

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

 

[Rich Grise]

I read in sci.electronics.design that Rich Grise <[email protected]>


There was an old lady of Bean
Whose musical ear was not keen.
She said, 'It is odd,
But I cannot tell 'God
save the weasel' from 'Pop goes the Queen'.

Bean is a village in Kent, which used to be a quiet backwater. Now it
has a motorway for bedfellow and a huge retail complex (Bluewater:
http://www.bluewater.co.uk/) for near neighbour. Soon it will have
another complex nearby.

Thanks! And of course, need I mention how rare a clean limerick is? ;-)

Cheers!
Rich