Ambisonics system calibration


    May 22 2012 | 11:50 am
    Hello All, Hope you are all well. I am finding this forum to be a goldmine of examples for patching and I am learning a lot...thank you.
    I am here again with another ambisonics question.
    As for my previous post, I am working on an ambisonics patch to prepare a concert with a jazz band in London in September. The patch is almost finished and is based on ICST tools (thank you very much for this!!!!) that is truly amazing!!!
    Now yesterday I came out with some thoughts on the calibration of the ambisonics system just before performing live (apart from the speaker location and distance from the centre)
    My ideas are:
    I need to simulate different places with a B format reverb but the space I will be performing as its own acoustic behaviour and this is quite difficult to eliminate. So I was thinking of using inverse filtering convolution by measuring the IR for each speaker of the rig and then calcuate the inverse filter and apply.
    This is quite a time consuming task and I am not sure it will provide a benefit to the system...also I am worried it can disrupt the beatiful encoding the ICST tools do.
    Do anyone here have any experience on this? Any example, even just written, would be much appreciated!!
    I will share all the work after I am confident it really works well!! but I will!!
    Thank you very much for all the help so far.
    Peace
    Bassik

    • May 23 2012 | 6:32 am
      "I need to simulate different places with a B format reverb but the space I will be performing as its own acoustic behaviour and this is quite difficult to eliminate. So I was thinking of using inverse filtering convolution by measuring the IR for each speaker of the rig and then calcuate the inverse filter and apply.
      This is quite a time consuming task and I am not sure it will provide a benefit to the system...also I am worried it can disrupt the beatiful encoding the ICST tools do.
      Do anyone here have any experience on this?"
      I have no experience of this. However, what you appear to be describing is room correction. This is not very different for Ambisonics than for stereo, 5.1, etc. It should not disrupt the decoding. (At the end, you will need to check that the bass has not been over-emphasised. This can also happen with stereo, 5.1, etc, but can be worse with Ambisonics.)
      Room correction will not eliminate the acoustic of the performing space but, providing this space is not highly reverberant, that is no big deal. Ambisonics can quite happily overlay a new acoustic on top of that of the performing space. In fact, this is what Ambisonics has always done in people's living rooms. See here for how it does this, particularly the next to last paragraph.
      Despite its name, room correction mostly corrects speaker defects, not room defects. This is A Good Thing, but is not your intended goal. Your intended goal is, sadly, unrealistic.
      Regards, Martin
    • May 23 2012 | 8:56 am
      Hello Martin,
      thank you very much. Very useful and accurate as always.
      "Ambisonics can quite happily overlay a new acoustic on top of that of the performing space. In fact, this is what Ambisonics has always done in people's living rooms."
      This is the most important fact for me!!!
      I will experiment a bit more and let you know...I have decided to implement a very simple room correction tool anyway so that I can check the difference between the 2 scenario but now I am quite confident that even if I do not manage to finish it on time, my ambisonics rig would work anyway.
      Regards, Bassik
    • May 23 2012 | 5:41 pm
      "'Ambisonics can quite happily overlay a new acoustic on top of that of the performing space. In fact, this is what Ambisonics has always done in people's living rooms.'
      This is the most important fact for me!!!"
      Note the qualifier: "'providing [the performing] space is not highly reverberant'"
      This is never a problem in living rooms, but might be a problem in some of your venues. Ambisonics can only add reverberation, not remove it. No speaker system can remove reverberation; removing reverberation requires acoustic treatment of the room.
    • May 23 2012 | 5:45 pm
      Hello Martin,
      thank you for the additional comment. OF course I am aware of the acoustic control of a room but I am starting from the fact that some rooms will be already treated while other will not.
      I believe it is in the skills of the sound engineer and performer to play with the place.
      Will let you know how I am progressing. :)