Cycling 74 » Topic: Ambisonic Time Stretching (Phase vocoders?)

Ambisonic Time Stretching (Phase vocoders?)

Laird0 — Fri, 21 Jan 2011 19:38:58 +0000

Hello Maxers,

I am working on an ambisonics project where I am trying to time stretch a B-format recording so that it will occur over less time without affecting the pitch.

My latest attempts have involved trying to use phase vocoders to perform the time stretching. I have tried a number of platforms for this including Logic 8, Audacity, Matlab and some command line programs. All of these seem to destroy the spatial aspects of the sound i.e. a sound that very obviously travels left to right in the recording is now completely ambiguous. Also the analysis/resynthesis is such that it sounds very processed.

I was wondering if anyone had any recommendations for resources or had any past experience in this? If there are any other software platforms or code out there I would be more than happy to explore those possibilities also, the more options the better!

Thanks in advance!

Re: Ambisonic Time Stretching (Phase vocoders?)

leafcutter — Fri, 21 Jan 2011 19:45:27 +0000

Try soundhack, I like it for stretching.

Re: Ambisonic Time Stretching (Phase vocoders?)

Laird0 — Fri, 21 Jan 2011 21:49:24 +0000

Thanks leafcutter

Very nearly had it all working with SoundHack. I managed to compress the audio files to 90% of original without too much tonal distortion or degradation of the spatialised audio. When I tried anything beyond that it introduced a regular click into the processed audio. I didn’t get round to testing if it was still spatialised though. Other combinations of values sadly didn’t get the desired effect

Time to hit some theory I guess, SoundHack looks really handy though, thanks for the heads up =)

Re: Ambisonic Time Stretching (Phase vocoders?)

Martin Leese — Sat, 22 Jan 2011 05:36:46 +0000

Try asking on the sursound e-mailing list. That is where the Ambisonic crowd hang out. Visit:

http://mail.music.vt.edu/mailman/listinfo/sursound

Regards,
Martin

Re: Ambisonic Time Stretching (Phase vocoders?)

sandbags — Sat, 22 Jan 2011 09:36:53 +0000

Since you’re asking in Max forum can I suggest elasticx~ which I just picked up myself to do some experiments with. Sounds pretty good to me but I’m not sure what your criteria are.

Matt

Re: Ambisonic Time Stretching (Phase vocoders?)

Roman Thilenius — Sat, 22 Jan 2011 13:59:16 +0000

if you dont want to loose any apsects of a recording
which is releated to phase … dont stretch it.

Re: Ambisonic Time Stretching (Phase vocoders?)

Tim Lloyd — Sat, 22 Jan 2011 14:10:35 +0000

Try ZPlane’s Elastique. Their site claims that stretching is phase-coherent cross-channel. I think it’s available as a plug-in, or you could use it within a licensed DAW such as Ableton 8 or REAPER, which both give you access to the highest quality Elastique algorithms and all the formant preserving options.

http://www.zplane.de/index.php?page=description-elastique#comp-chart

Re: Ambisonic Time Stretching (Phase vocoders?)

Laird0 — Sat, 22 Jan 2011 15:04:55 +0000

Great stuff thanks for the replies so far guys, very helpful.

In the process of trying Sursound, need to sort out permission to post, I’ve been a long time lurker on the list but never posted for some reason. Hopefully will get it sorted soon. If only the symposium was this weekend! ;)

I will have a look at both elasticx~ and Elastique also.

Not that it really worked for what I needed but I was really impressed by the patches made by Jean-Francois Charles http://www.cycling74.com/share.htm, really good for freezing and extreme slowing.

Thanks again folks