[Vorbis-dev] Ambisonics in Ogg Vorbis

[Richard Lee]

Paul Martin wrote :

>> In "SHELF FILTERS ... ", I use WXYZ in its strict Ambisonic sense as defined in

 http://www.york.ac.uk/inst/mustech/3d_audio/secondor.html

>You're dancing round the question. The specification of an AMB file says that the W channel will be stored at a level of -3dB.

http://www.ambisonia.com/Members/etienne/Members/mleese/file-format-for-b-format

> "The W channel is attenuated by -3 dB (1/sqrt(2)) for all orders.  That is to say, a source at 45 degrees azimuth (zero elevation) wouldproduce equal gains in W, X, and Y."

> This means that my decode *is* the "Energy" one.

You've just described an ENCODING issue.

Your DECODER

> 0.3536,0.3536,0.3536,0.3536,\
> 0.1768,0.1768,-0.1768,-0.1768,\
> 0.1768,- 0.1768,-0.1768,0.1768,\

as Sebastian Olter points out is a "Cardioid" decoder.  Its OK but an "Energy" decoder is better and an "Energy" decoder with Shelf filters is better still.




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