Time-Stretch Encoding for Power Pack

[MikeCerm]

I found an open-source time-stretching/pitch-shifting library. It can be found here: http://www.surina.net/soundtouch/
I don't have a lot of programming knowledge, but it should be pretty easy to make a Power Pack DSP effect to allow time-stretching/pitch-shifting using the library.

I listen to a lot of podcasts. Most podcasts are delivered as MP3's at bitrates of 64K or higher. To save time and space, (using dMC File Selector) I convert all of the podcasts I download to WMA-Voice at 12kbps. I then listen to the WMA files in Windows Media Player at high speeds, so I can get through more podcasts in less time.

Speex is much more efficient, both in encoding speeds as well as quality/filesize, but Media Player can only time-stretch MP3 and Windows Media files. I would like to time-stretch during the encoding process.
I'm also a musician, and I often need to transpose (pitch-shift) songs, or decrease the tempo of songs to transcribe difficult passages. A Power Pack DSP using an intermediate wave file and the library at the link above would be a really great addition to the suite.


The library is LGPL. If there's a licensing problem, maybe you could offer the feature an a separately installed option so you wouldn't have to open up any of your source-code (if that's what the LGPL would require, though I'm not an expert on open-source licensing).

You could also write your own algorithms, but that would probably be a little bit harder, and this is a feature that I've been hoping would be added for some time now.

Thanks!

[LtData]

Re: Time-Stretch Encoding for Power Pack

Note that there is already a codec for Speex: http://www.dbpoweramp.com/codec-central-speex.htm
Have you checked to see if it does time-compression/stretching or tempo changing?

[MikeCerm]

Re: Time-Stretch Encoding for Power Pack

Of course it doesn't! It's just an audio compression codec, no different from any other codec. Time-stretching can be handled by the library above, which is also available as a binary, but it only accepts wave input. So for me to do what I'd like to do, I would have to use dMC to convert to WAV, run the time-stretch binary (from the command-line), and then convert the output to Speex. I'd lose the tags if I did it that way, and it's too many steps. I just want it to be an option from the Power Pack DSP menu, which shouldn't be too difficult to implement, given the back-end processing is already written (see link in original post). It would just be a matter of writing a little GUI for the PP DSP menu, and pluging in the code the same way all the other DSP functions work.

[ChristinaS]

Re: Time-Stretch Encoding for Power Pack

Spoon's been working on keeping some kind of id tags with wav files as well. Probably early days yet, but that may go some way to solve your problem, eventually.

In any case, if your file is named properly to reflect id tags, you can most likely recover id tags by retagging from file name.

[MikeCerm]

Re: Time-Stretch Encoding for Power Pack

I know Spoon's working on tagging wave files which would be cool, especially if other software could properly interpret the tags (as well as my Creative Zen Vision:M), but I'd still like to have a DSP time-stretching feature. There are plenty of DSP features that I don't use (Invert, DC Offset?), so it would be nice to have one that I would. Time-stretching would be far more useful, and not too difficult to implement. It's a feature that's very common in audio apps, and it would be nice to format convert and time-compress/pitch-shift in one easy step within dMC. If dMC was open-source, I'd implement it myself, but since it's not, I've got to ask Spoon to do it for me.

[Spoon]

Re: Time-Stretch Encoding for Power Pack

http://www.dbpoweramp.com/developer-dmc-dsp-effects.htm

[MikeCerm]

Re: Time-Stretch Encoding for Power Pack

Hey, ask and ye shall receive! Thanks Spoon, and if I have any luck, I'll submit my plug-in. The last thing I submitted was the Ogg Vorbis aoTuV encoder and GUI, and I'm really happy to see it's being distributed. I also like that it's being kept up to date with the most recent aoTuV versions and SSE optimized builds. Thanks again!