[LAD] Musescore "music trainer"?

[Tim E. Real]

On November 12, 2010 12:48:47 pm Ralf Mardorf wrote:
> On Fri, 2010-11-12 at 18:32 +0100, Dominique Michel wrote:
> > Le Fri, 12 Nov 2010 00:54:58 -0500,
> >
> > "Tim E. Real" <termtech at rogers.com> a écrit :
> > > On November 11, 2010 11:06:10 pm Dominique Michel wrote:
> > > > Le Thu, 11 Nov 2010 16:43:41 -0300,
> > > >
> > > > Camilo Polymeris <cpolymeris at gmail.com> a écrit :
> > > > > >> For me, a stand alone pitch detection application would be
> > > > > >> better :
> > > > > >>
> > > > > >> audio in -> pitch detect -> midi out
> > > > > >>
> > > > > >> You plug the instrument into the audio in, connect the midi
> > > > > >> out to any midi in in qjackctl, and it is just to play some
> > > > > >> melody.
> > > > > >>
> > > > > >> Ciao,
> > > > > >> Dominique
> > > > > >
> > > > > > There is aubionotes (http://aubio.org/aubionotes.html), which
> > > > > > claims to do exactly what you want. Don't know how well,
> > > > > > though. I am trying to connect it to PianoBooster, to see if
> > > > > > that could be a solution. WaoN could also be an option, I'll
> > > > > > try that next. Eventually, I'd like an integrated app.
> > > > > >
> > > > > > Greetings,
> > > > > > Camilo
> > > >
> > > > Thanks for the tip !
> > > >
> > > > > Ok. If someone is interested: I can report that aubionotes works
> > > > > quite well for the samples I tried (brass mostly, all
> > > > > monophonic). WaoN is similar, maybe even better, but doesn't work
> > > > > realtime, it handles pre-recorded samples, only.
> > > >
> > > > Same thing here. I think that it must use some kind of fft. The
> > > > problem with fft and realtime is not the processing power but the
> > > > time it take before you get a sufficient amount of samples in order
> > > > to be able to run the fft.
> > > >
> > > > Ciao,
> > > > Dominique
> > >
> > > Exactly. I was going to start a thread asking about this. Mind if I
> > > pitch in? Difference between lowest note on a guitar and next note is
> > > very small, requiring large number of FFT bins. (If you play a flute,
> > > you're lucky.) You can put a crappy time domain style pitch shifter
> > > ahead of the converter to reduce this. (A good freq domain PS may
> > > have more latency.) It's fun. With practice a normal guitar becomes a
> > > piano etc...
> > >
> > > I've seen polyphonic products advertised claiming zero or near zero
> > > latency. How do they do it?
> >
> > I don't know. If you take a guitar synthesizer, it have a polyphonic
> > mic, that is one mic per cord (similar to a simple humbucking per note).
> > They certainly make 6 monophonic note extractions.
Yes, there are guitar synthesizer kits, which use a multi pickup with
 six individual outputs. Some come complete with a special guitar.
Having multi pickup with six individual outputs is certainly the best way.
Then you only need six easy mono synthesizers.
But what I am talking about is using a normal guitar with a normal
 pickup, and using FFTs to make a polyphonic converter.
It works, but of course it's far from perfect.

> >
> > Guitar mics take in account only the vertical movements of the cords,
> > the output signal is the derivative of this movement.
> >
> > Also, the harmonic content of a guitar note is not constant. During the
> > attack, the value of the fundamental is the most important signal in
> > the note, but during the sustain, the value of the fundamental decrease
> > very fast and the second harmonic become the highest tone in the note.
> > It is even more complicated when the cord touch the frets because you
> > will get false maximums of the signal. You can also get hum with a
> > simple humbucking, and you will get saturation with a double humbucking.
> >
> > > I've used FFT, but when told of this delay problem, my friend keeps
> > >  telling me no, use Laplace transforms. When I studied them (looong
> > > ago), I could not fully understand how to apply the knowledge.
> > > Is there a Laplace library out there?
> >
> > I am not sure, but the FFT is a particular case of the bipolar Laplace
> > transformation, 
Yes, that is how I understand it.
> > so I don't think than the necessary time to get enough
> > samples in order to get a reliable result would be better. The worst
> > case scenario depend on the lowest note you will able take in account.
> >
> > > Wavelets? I studied those as well, but my meagre brain could not
> > > cement.
> >
> > If it is what I call "filtre en peigne" in French (comb filter), it can
> > be an alternative. It is DSP algorythms for them, but I don't know if it
> > is something for a PC processor.
Oui, il y' a des plugins LADSPA qui donne les fonctions 'comb filter'.
(Pardonnez mon Francais, en Canada, nous sommes censés être bilingues!)

> >
> > > To catch the higher notes first, how about n FFTs with n samplers
> > > driven by n separate even-tempered clocks, where n is the desired
> > > number of notes? For ex. 3 octaves, 36 FFTs. I forget why, but I
> > > think that didn't work out. I think the pesky relation giving the
> > > delay kept getting in the way. You increase the sample rate and you
> > > just end up increasing the delay because you need more freq bins for
> > > the same given resolution. The delay is really governed by the
> > > smallest difference in notes you want to detect. In guitar's case, I
> > > found it just passes as acceptable.
> > >
> > > Tim.
> >
> > The fastest algorithm would be to find the maximums of the signal.
> > The time between 2 consecutive maximums = the period of the note.
> > The delay would not be constant, but it would not exceed 1+1/2 periods
> > of the note in the worst case. In practice, it would be something
> > between 1 and 1+1/4 periods of the note in most (all?) cases.
> >
> > This will be very easy with an instrument like a flute, but much more
> > difficult with an instrument like a guitar, because you will have to
> > take in account the false maximums possibility (when you play very
> > hard on the cords or when you have a not so good guitar) and the
> > sustain of the note.
> >
> > Ciao,
> > Dominique
>
> Pardon, I didn't read the whole thread, but just this email and I'm a
> guitarist.
>
> Imagine a Jimi Hendrix common E7#9 chord or something similar.
>
> Translation from the guitar strings to a piano isn't easy for
> automation! It's easy for a jazz musician ;), but nearly impossible to
> "translate" by a computer from an instrument like the guitar, to an
> instrument, like the piano.
>
> Again, I don't know what this thread is about, but at least some chords
> can't be taken from the guitar, to the piano, without some human
> imagination about the wanted effect.
> 2 Cents,
> Ralf
Yes, of course, this polyphonic FFT technique is fraught with difficulties.
Guitar strings are so rich in harmonics, that false triggering is a
 real problem. And complex chords often trigger the wrong notes.
So the makers of such software recommend that the tone knob is 
 turned down, and a clean sound is used, usually using the neck pickup.

However in usage, I was able to play chords and solos, boogie-woogie 
 and such, and the software did a pretty neat job. 
It's very entertaining.

Tim.