[CM] ambix ambisonics command line

[Juan Reyes]

Hi Nando,

Thanks a lot and I mean a lot!

Been reading all pointers you are telling us in addition to various
papers you wrote with Aaron Heller and of course the Sphear slides and
documentation. Not just last night!,  ...should say for months.

Things are much clearer now.

Maybe what's going on is that we use ready made software like Fons'
Ardour panners or even AmbPan in Supercollider (real time) and we never
look under the hood. They just work. But this is valid until you get
into unique situations and, ... " there you are on your own".

All of your explanations make fuzziness go away. However, I can't deny I
need to sit down to read the code of 'alocsig-acn'. Thanks for sharing
it. My take on the FOA encoder is as you are suggesting, using the
canonical equations and thus passing signals through Ambdec.

"Curiosity killed the cat". You are mentioning, "The Hidden and
Mysterious Machinery of Sound". Can wait listening to it.

Best of all,

   -- Juan


> 
> If you want to pan sound in an Ambisonics soundfield then the four 
> equations that Anders posted would be a start for a first order 
> soundfield "encoder" for the FUMA format (mono input, 4 channels wide
>  output).
> 
> 
> 
> See the attached scheme file for a panner (encoder) I wrote a while 
> back[*]. This will pan a mono signal in Ambisonics and create a 5th 
> order ACN/SN3D (aka Ambix) soundfile (36 channels wide). If you want
> 2nd order you would use just the first 9 output channels, the first
> 16 for third order, etc. This also creates a second scaled soundfile
> to feed an Ambisonics reverb.
> 
> No idea if this code still works, I wrote it for "The Hidden and 
> Mysterious Machinery of Sound" back in 2015... Time flies...
> 
>> - Now the confusion between FUMA and Ambix -.
> 
> No confusion :-) Just the most popular formats. FUMA is the original
>  historical one, defined only up to third order, Ambix (ACN/SN3D) is
> the current one, widely used. Two main differences: order of the
> components (FUMA == WXYZ/etc, ACN == WYZX/etc), and the weights of
> each component. Your microphone or your encoder (panner) will
> generate one of them. You want to always use the same format when
> mixing, if you have different formats you have to convert to one of
> them (there are utilities to do that).
> 
> https://en.wikipedia.org/wiki/Ambisonic_data_exchange_formats
> 
> And once you have your Ambisonics mix you will need a decoder for
> your speaker configuration... BTW, the decoder will decode a
> particular format, so you better feed it the right one or things will
> be wrong (spatially).
> 
> :-)
> 
> The whole story fills books... -- Fernando
> 
> [*] the equations come from a encoder generator written by Aaron
> Heller that can write them in several languages, very handy.
> 
> https://bitbucket.org/ajheller/symbolic_spherical_harmonics/src/master/
>