Ambisonic Time Stretching (Phase vocoders?)
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!
Try soundhack, I like it for stretching.
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 =)
Try asking on the sursound e-mailing list. That is where the Ambisonic crowd hang out. Visit:
if you dont want to loose any apsects of a recording
which is releated to phase … dont stretch it.
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.
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