[ddots-l] Re: Changing tempo and stretching audio

Gudrun,

The midi data is elastic, and it doesn't matter what
it is expanded or contracted to tempo-wise as it will
stay intact.  Audio on the other hand is not so easily
expanded or contracted.  Although it can be done as a
whole audio file, it is better to use a program that
divides the audio file into recognizable transients. 
It then matches those to the new tempo as best as
possible.  

Here's a quote about Rex files from Keyboard magazine
online:

"REX file: A type of digital audio file designed for
easy time-stretching. The file is divided into small
slices, which are triggered sequentially by MIDI data.
If you slow down the tempo of the triggers, the slices
play further apart, thus stretching the file so it
matches the slower tempo. The opposite happens if the
triggers are closer together.
REX files work best with percussive files that have
sharp initial transients, as these help define an
unambiguous slice start. Sustained sounds work between
as ?acidized? files, which use a sophisticated
combination of slicing and DSP, or simply offline
stretching using a digital audio processing algorithm,
such as the MPEX3 algorithm included with Sonar."

If your two audio tracks aren't likely to convert
well, perhaps just recording those two over atop the
newly sped up MIDI tracks would be the way to go to
not have too much rework to do.

I'm sure others here will have better advice on
stretching the audio to fit the MIDI.

Doug



--- Gudrun Brunot <gbrunot@xxxxxxxxxx> wrote:

> I've recorded a piece or music that has midi
> instruments on trackas 1-17 
> (not all recorded), and guitar on audio tracks 18
> and 19.  I selected 85 as 
> the tempo, nice and slow.  Now, I'd like to speed it
> up to 95 or 100.  I 
> tried selecting all the tracks from beginning to
> end, fit to time, new thru 
> time (subtracted a few seconds), tempo map, stretch
> audio.  Waited an 
> eternity, and the midi and audio were out of sync. 
> Tried the length 
> dialog, and same thing happened.  What should I do. 
> I can undo and not 
> save the changes, so my work isn't ruined.  However,
> I'd like to speed it 
> up a tad.
> 
> Gudrun
> 
> Gudrun
> 
> 
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