Ambisonic Time Stretching (Phase vocoders?)

    Jan 21 2011 | 7:38 pm
    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!

    • Jan 21 2011 | 7:45 pm
      Try soundhack, I like it for stretching.
    • Jan 21 2011 | 9:49 pm
      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 =)
    • Jan 22 2011 | 5:36 am
      Try asking on the sursound e-mailing list. That is where the Ambisonic crowd hang out. Visit:
      Regards, Martin
    • Jan 22 2011 | 9:36 am
      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.
    • Jan 22 2011 | 1:59 pm
      if you dont want to loose any apsects of a recording which is releated to phase ... dont stretch it.
    • Jan 22 2011 | 2:10 pm
      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.
    • Jan 22 2011 | 3:04 pm
      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, really good for freezing and extreme slowing.
      Thanks again folks