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ICST Ambisonics Tools Panning Issue

Feb 08 2013 | 12:49 am

Hi everyone,

I have a bit of a strange issue here that I need confirmation on whether it is really a problem or my part or if it’s just an issue with the created objects – any help would be thoroughly appreciated here! I’m doing an honours project on ambisonic surround sound and part of that project involves a comparison between synthesized ambisonics and ambisonics recorded with a sound field microphone – digital vs. analogue debate so to speak.

The problem I have is really weird. I wanted to test out the tools in a 5.1 setup within my university which has access to max 5 and a 5.1 system which I will be using. Initially I thought the patch worked – the ICST tools are supplied with an example patch and I only slightly modified the 06_Full_Audio_Chain.maxpat that comes with it ( i removed the delay sub patch for the speaker feeds as I didn’t need it since the room is so small, along with changing the encoding/decoding type to furse-malham and the navigation system to gerzon’s acoustics).

The issue I have is that the sound source seems to pull itself towards the back left speaker once the sound source moves behind me, then quickly just pulls itself forward to in front of me when it is at 6 o’clock point on the ambimonitor object. I’m using a 1st order system at the moment, but I’ve even tried moving it up to 3rd order, changing the encoding/decoding type and even the navigation system used – nothing fixes the problem at all. I’ve also tried moving my own position to see if I wasn’t in the right spot but that isn’t it either – I’ve literally tried everything and more here. I used version 2.0 in the studio though I have just noticed there’s an update – maybe it’ll fix it.

So to check that it wasn’t the speakers at fault, I opened up a protools session and just panned a mono sound file into the 5.1 system – it worked BETTER than the ambisonics system (which I can’t believe is right) and there’s no pulling of the sound source towards speakers unlike the max objects. If there is no problem then that’s fine, will just make for some more interesting answers for my project, but I just want to be 100% clear on this so if anyone can test my patch on another 5.1 system that would be much appreciated – hopefully it’s just the case that I’ve missed something though I can’t understand what!

Feb 08 2013 | 12:52 am

To add to that, I did try using it with the delay sub-patch as well but it did not work either. And of course, here are the externals I’m using:

Feb 08 2013 | 1:52 am

The example works fine here on my quad speaker layout and clearly moves slowly around the field, as expected.
The problem you experience sounds very much like the audio channel to speaker mapping is inconsistent with the layout of the speakers required to reproduce this example. Check what the default channel mapping is on the audio hardware to the speakers on the system you are using and then set the MSP audio i/o Mappings (bottom of the Audio Status window) to suit that. If that creates problems of compatibility for other patches, users etc, you could crete another speaker layout [p standard_speaker_setups], which you would definitely need to do if the physical speaker configuration varies from the setup defined in that patch…

PS using copy compressed in max and pasting the example in your post (rather than attaching )is generally easier for other users.

Feb 08 2013 | 10:02 am

" I wanted to test out the tools in a 5.1 setup within my university which has access to max 5 and a 5.1 system which I will be using"

Be careful with this sort of test. Generating Ambisonic decoders for irregular speaker shapes (such as ITU) can result in multiple ‘correct’ sets of numbers. Also, I don’t think the ICST tools have irregular decoder tools in them (moving the speakers, as far as I remember, doesn’t actually alter the decoder as it would need to……). So, given this, I would expect the Pro tools panner, which is optimised for the ITU layout to perform better, even with your system setup correctly (I’m assuming that ‘better’ here is referring only to localisation accuracy…..)



Feb 08 2013 | 12:02 pm

Spectro I think you might be right, the more I think about yesterdays session the more I realise that the mapping might’ve been inconsistent – I remember that there was nothing showing on channel 2s output on the mixing console and it also skipped number 6, instead playing out of 7. I’ll check this out and report back – good to know it’s just me so cheers for that!

Bruce I’m not too sure what you’re meaning by "irregular speaker shapes can result in multiple correct sets of numbers" could you elaborate? 5.1 ITU is a standard speaker layout for 5.1, or are you referring to the absence of an additional channel to cover the back end? There is a preset too in ICST ambisonics for 5.1 ITU which I am using.

I’m actually not concerned if it does play in 5.1 amplitude panning’s favour, I just want to find out if ambisonics validity stretches down to a relatively low number of surround speakers or whether the real benefit is found in larger setups.

PS If anyone else does have a 5.1 system and could report back their findings also that would be great too. :)

Feb 09 2013 | 7:06 pm

Any other thoughts on this then?

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