View Full Version : Gradual speed/pitch correction???

2006-02-15, 10:21 PM
I've gotten a bit into speed/pitch correcting some of the shows I get lately. Usually it's the older shows with a few analog tape generations that tend to have this problem most often.

I use Cool Edit Pro's Pitch Bender function, and adjust the speed/pitch by comparing to a guitar tuned to A=440. This is pretty straight forward when one constant adjustment is required, but I've noticed that some shows are not off by one constant speed. They sometimes get more or less sharp/flat as they progress, such as if a tape recorder/player somewhere in the lineage was gradually running out of battery power over the course of the recording.

So, is there a way to increase or decrease the speed of a wav file gradually over the length of the wav? Has anyone done this?

2006-02-16, 03:53 PM
Pitch Bender is the tool you need to use to increase or decrease the speed of a wav file gradually over the length of the selection. unless the graph is set to a perfectly straight horizontal flat line, it will speed up/slow down gradually based on what is plotted there. if you want to apply one pitch correction to an entire show you need to join the tracks, select all and use the more appropirate tool "Stretch" in resample mode (preserves neither pitch nor tempo) or "pitch bender" with a perfectly flat horizontal line on the graph. always set the quality to maximum when you apply the final settings. then the show needs to be re-cut on the sector boundaries, FLAC'ed, tagged, fingerprinted, what have you.

If you have a tape which speeds up and slows down, you would have to find how to exactly compensate those problems using the graph (which is mind-boggling to say the least). You could also work section by section if that helps, but before applying the effect each time you have to be sure that the end of the selection is on a zero crossing so as not to introduce clicks/crackles on the seams. also zoom in on each seam (around a second or two) and look at it in spectral view toggling undo/redo to see if a red post-like artifact is being introduced (in which case make sure you are on the zero crossing & try again, perhaps moving the selection).

be forewarned this is very advanced & time-consuming work. one-step pitch correction of an entire show is difficult enough but calculating the speed variations of an entire show accurately is thousands of times harder than that! I wish you the best, work slowly and carefully and make sure the show is a real favorite of yours.

2006-02-17, 09:31 PM
small edit, I meant "zero crossing" where I put that in