Adjusting playback speed but not pitch (1G iPod Mini)

[hendersj]

I see that this topic has come up a few times in the past, but there doesn't seem to be a definitive answer on the question (found one thread from a couple years ago that said it was being implemented, but the thread was about the iRiver players).

Like the posters in the other threads, I could see this being useful for audiobook playback or other similar things - where the speaker is too slow or too fast.  Another use I can see is for musicians - when practicing a fast piece of music, it often is helpful to run at a slower speed.  Having different pitches throws the live performer off on pitch precision as well.

I used to play violin, and sometimes if I was having difficulty with a piece of music, I'd listen to a recording to try to figure out what I was doing wrong.  If I could keep up with the recording, I'd try to play along as well.  But if I could set the playback speed without modifying the pitch, I could gradually increase the speed on subsequent rehearsals in order to help my fingers memorise the patterns they needed to learn.

And of course for DJ'ing, I could see practical application there - though in that implementation, it would be helpful to know what the playback time was going to be for the current track with the adjustment - so there might be a little more work to do for that option.

[AlexP]

Sorry, what is the actual question?

[Llorean]

I don't see an actual question in your post. Are you asking if it's supported? No it is not. Are you asking if it's being worked on? If so, the forums really aren't for asking for status reports. Are you requesting someone work on it? If so, that belongs on the feature request tracker, though it seems quite likely there's already a request.

[hendersj]

Sorry, I guess I did miss asking an actual question.  Wondering if this is something under consideration, being worked on, or an idea that isn't of interest to many.

If there's a better place to look, I'm happy to look there - still kinda getting used to where things are on the site.

[pondlife]

There's a patch to do this - see http://www.rockbox.org/tracker/task/8894

It's designed for speech, and only works in mono at the moment.  Plus it will likely reduce your battery life somewhat (or generally use plenty more CPU).

I'll also add a call for anyone who understands this sort of stuff to see if they can improve the patch enough to get it into SVN...

pondlife

[Strife89]

Isn't there a plugin for Audacity for this sort of thing? Perhaps it could be ported.

Just a thought - don't stone me to death.

[hendersj]

Thanks for the feedback guys, I'll have a look at the patch and see if that'll do what I'm looking for.  Extra CPU doesn't bother me - with no extras turned on I get about 8 hours out of my iPod as it is, but for me this would be generally for listening ripped MP3 files from audiobook discs - though I do have some old radio shows that run an hour that I'd reduce to 45 minutes for my drive to work as well.

[GodEater]

Extra CPU usage might not bother you in terms of battery life, but it might bother you if it doesn't leave enough for your music to play properly...

[hendersj]

That's true, but I've noticed occasional bumps when using the pitch shifter as well if I adjust it too far out.  It seems to help with the pitch shifter to increase the anti-skip buffer.

[DancemasterGlenn]

The Audacity plugin uses the soundtouch library (found here), which was also used to make the pacemaker plugin for winamp. I don't know how portable the code is, but it would be cool to see it used in rockbox. I've spoken with the guy who coded it before, and he's pretty good natured. Anyone want to check out his code?

Another possible library to use would be rubber band (here), but I don't know about the portability of that code either.