Subject: Re: [linux-audio-user] Note tuning and quantizer in audio files
From: R Parker (rtp405_AT_yahoo.com)
Date: Tue Jul 06 2004 - 11:23:05 EEST
Thanks for the information. I was unaware of audio
quantization--definitely an interesting capability.
What pitch, time stretch and quantization libraries or
Linux audio applications are you aware of that have
High quality audio pitch, time stretch and
quantization would all be very useful in a DAW like
Ardour. I work on enough projects that require
extensive editing or rebuilding that command line
example applications for a library would be useful.
Alex, are you the person who announced their intention
to develop these types of libraries on the Linux
Consortium mailing list?
--- Alejandro Lopez <alex_osiris_AT_hotmail.com> wrote:
> Hi again,
> Just to briefly explain these two nice techniques as
> a couple of you have
> asked about them. They are both based on the same
> math, a kind of modified
> fast fourier transform which enables the software to
> stretch or shrink time
> without affecting pitch or sound timbre (the
> characteristic that enables us
> to recognize an instrument).
> Note tuning, only applicable to samples of
> monophonic instruments: the
> software has a freq detector that will find the
> nearest note to what is
> being played. It will find a starting time, end time
> and deviation for that.
> Then it will apply this FFT to generate a sample
> equal in duration but in
> tune. This is done by stretching or shrinking as
> appropriate first (this
> does not change pitch), then re-sampling to length
> which changes the pitch
> as required.
> Quantizer: only used for samples of percussion
> AFAIK, but should be
> applicable to other instruments with high attack
> like bass and others: first
> step is for the software to identify the location of
> the notes (that's the
> equivalent for MIDI events but this time in audio),
> by using a kind of peak
> detector this time instead of the freq detector for
> the other technique.
> Second step is to identify where the notes should
> exactly be time-wise. For
> this, it's neccessary that the software knows about
> the timing of the song /
> sample! (basically BPM and desired quantize
> resolution). Knowing this, it's
> pretty straightforward to "shrink and stretch"
> before and after the note so
> it falls exactly on time.
> These two give best results when the notes are not
> too off. This is due to
> this special FFT not being a perfect method to
> extract exactly everything
> that's there, especially high frequencies. Different
> implementations of
> these use different algorithms, all are based on a
> FFT, but some use
> different techniques to mask certain side effects
> that appear on the
> modified sample. Some implementations are very
> impressive I have to say, and
> they can stretch or shrink to say two times or half
> with brilliant results.
> All pretty impressive technology which has been
> around for a while now..
> Horóscopo, tarot, numerología... Escucha lo que te
> dicen los astros.
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