[CM] ambix ambisonics command line

[Fernando Lopez-Lezcano]

On 6/6/24 11:38, Juan Reyes wrote:
> Hi Anders,
> 
> Thanks a lot for your thorough explanation which of course as usual is
> useful and encouraging. What I was looking for was something like
> 'tetrafile'. (Been using other Fons' software for a while and don't know
> how I overlooked at it).
> 
> Need to encode few dozen sound files into B-format Ambisonics and batch
> processing would be a time saving alternative.

Hey Juan,
I am assuming you need A-format (capsule signals) to B-format 
(Ambisonics) conversion. As Anders wrote, that is heavily dependent on 
which Ambisonics microphone was used to record the soundfield.

Which one did you use?
-- Fernando


> Will be following your
> suggestions.
> 
> However, while searching this topic, can't help pointing out Fernando's
> Ambisonics code in 'dlocsig.clm (scm)'.
> 
>     -- Juan
> 
> 
>>
> 
>> If all you want is the MS-type matrixing it should be straight
>> forward in an "a2b.scm" script for snd, or sox or ffmpeg or others,
>> You can combine the 4 A-format channels FLU,FRU,BLU,BRD using 
>> MS-like-techniques:
>>
>> W = FLU+FRD+BLD+BRU X = FLU+FRD-BLD-BRU Y = FLU-FRD+BLD-BRU Z =
>> FLU-FRD-BLD+BRU
>>
>> But leaving out all the required tunings for A2B conversion from any 
>> given FAO mic: eq, gain, phase - you wont get any meaningful
>> B-format output - rather a
>> "quite-nice-space-like-feeling-surround-spread mic" (wow, my new
>> brand!  :-) .
>>
>> For B-format you'll need a specific B-format encoder to a specific
>> type of mic, tuned to its geometry and specs of capsules, and further
>> using precise calibration-data fitted to your personal mic (*).
>>
>> Fons Adriansens 'tetraproc' includes a CLI 'tetrafile', doing the
>> A-B conversion for Core Sounds Tetramic, and similar for their
>> 2nd-order Octomic.  I think he has some example *.tetra config-files
>> for some other brands.  He also offers to do the necessary
>> measurements and calibrations for your TetraMic to plug into his
>> conversion tools.
>>
>> Not sure what the other brands - Sennheiser, Röde etc. - offers for 
>> CLI-versions of their tools.
>>
>> (*) The dependence on both a specific decoder for a mic-brand, and 
>> further individually calibrated per mic, is perhaps sub-realised? 
>> Strange, given Ambisonics 100% reliance on extremely exact phase and 
>> gain info to represent the recorded space.
>>
>> One example is Nevaton who provides their VR-mic - otherwise very
>> nicely made with great sound (no-noise, full-range - and very
>> expensive) - without neither a fitting A2B decoder or necessary
>> calibration data for each mic, relying on a one-time measurement of
>> one mic done by Angelo Farino.  They even have suggested using
>> Sennheisers or Röde's standard A2B-encoder...
>>
>> -anders
>>
> 
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