30 Sep
2010
30 Sep
'10
4:01 p.m.
On Thu, September 30, 2010 3:47 am, Robin Gareus wrote:
Yes, but its implementation is not very well done.
But nothing wrong with having it jackified for ease of use. Especially if
the portaudio code is as you suggest. No doubt someone will take the time
if it is a good piece of software otherwise.
--
Patrick Shirkey
Boost Hardware Ltd.
On 09/30/10 09:40, Patrick Shirkey wrote:
I suppose you missed the various windows he has added. Maybe they are just
there for show?
On Thu, September 30, 2010 12:01 am, Louigi Verona wrote:
Are you sure? Where did you get that info from?
Just skimming over Stretch.cpp gives me the impression that it's based
on Fourier analysis and re-sythesis.
http://en.wikipedia.org/wiki/Fourier_analysis
The process() loop looks like:
{
apply_window();
smp2freq(); // Fourier Analysis
process_spectrum();
freq2smp(); // Fourier Synth
}
In layman terms:
There's a smart French guy by the name of Joseph F. sitting inside it:
If you play him some audio: He thinks: "Hey, this is actually just a few
simple sine-waves added together (superpositioned)", he quickly
calculates their frequencies and amplitudes and asks "Now, you want to
change the duration?" easy: "I'll generate some new sine-waves with
these frequencies and amplitudes, how long did you say you want?"
(The smart thing about this French guy is that he actually speaks fluent
English - Sorry I could not resist :) Hey guys!
I have two questions.
1. How does Sound Stretch work? It is incredible the way it can produce
a
tone which has no noticeable vibrations, just a wall of sound. How is
that
accomplished, in layman terms if possible :)
It grabs a section of the audio and copies/multiplies it then appears to
apply some pretty neat math to smooth it all out funnily enough using a
selection of windows to get the best result. 2. Can this program be jackified and is that a
lot of work?
It uses portaudio. Doesn't that have a jack output? Otherwise yes, he has designed it so that adding
jack support would be
fairly trivial.
Indeed, to change the integrated player to output to JACK would be
trivial. It currently uses the PortAudio's StreamCallback which is very
similar to JACK's process callback.
Using it to do "live" timestreching with JACK (jack-in -> jack-out) is
AFAICT impossible because:
<details>
If you feed it N samples (or seconds) of audio you end up with M samples
(or seconds) with M > N.
One could do a kludge:
eg. for a 1:10 time stretch with continuous output:
- read 1 sec of audio from the input
- ignore 9 secs of the input
but I don't think this will be useful.
</details>