bformdec2

An opcode for decoding Ambisonics signals in Csound, with dual--band decoding and near--field compensation.

Compile

Linux:

g++ -O2 -shared -o <path to opcode64 folder>/libbformdec2.so -fPIC bformdec2.cpp -I <path to csound headers>

Examples of paths:

<path to opcode64 folder> --> /usr/lib64/csound/plugins64
<path to csound headers> --> /usr/local/include/csound/

OSX:

g++ -O2 -dynamiclib -o <path to opcode64 folder>/libbformdec2.dylib bformdec2.cpp -DUSE_DOUBLE -I<path to csound headers>

Examples of paths:

<path to opcode64 folder> --> /Library/Frameworks/CsoundLib64.framework/Versions/6.0/Resources/Opcodes64 
<path to csound headers> --> /Library/Frameworks/CsoundLib64.framework/Headers

Sintax and usage

aout[] bformdec2 isetup, abform[], [idecoder, idistance, ifreq, imix, ifilel, ifiler]

Initialization

Note that, as in bformdec1, horizontal angles are measured anticlockwise in this description.

isetup –- loudspeaker setup.

There are eight supported setups:

1. Stereo - L(90), R(-90); this is an M+S style stereo decode.
2. Quad - FL(45), BL(135), BR(-135), FR(-45). This is a first-order decode.
3. 5.0 - L(30), R(-30), C(0), BL(110), BR(-110). Note that many people do not actually use the angles above for their speaker arrays and a good decode for DVD etc can be achieved using the Quad configuration to feed L, R, BL and BR (leaving C silent).
4. Octagon - FFL(22.5), FLL(67.5), BLL(112.5), BBL(157.5), BBR(-157.5), BRR(-112.5), FRR(-67.5), FFR(-22.5). This is a first-, second- or third-order decode, depending on the number of input channels.
5. Cube - FLD(45,-35.26), FLU(45,35.26), BLD(135,-35.26), BLU(135,35.26), BRD(-135,-35.26), BRU(-135,35.26), FRD(-45,-35.26), FRU(-45,35.26). This is a first-order decode.
6. Hexagon - FL(30), L(90) BL(150), BR(-150), R(-90), FR(-30). This is a first- or second- order decode.
7. 2D binaural configuration. This first decodes to a octagon configuration and then applies HRTF filters.
8. 3D binaural configuration. This first decodes to a dodecahedron configuration and then applies HRTF filters.

idecoder -- optional (default 0), select the type of decoder

0. Dual decoder (velocity and energy decoders using dual-band splitting).
1. Velocity decoder.
2. Energy decoder.

idistance -- optional (default 1 meter), select the distance (in meters) to the loudspeaker (radius if regular configuration)

ifreq -- optional (default 400 Hz), frequency cut (Hz) of the band splitting filter (only has an effect if idecoder=0)

imix -- optional (default 0), type of mix of the velocity and energy decoders' outputs

0. Energy
1. RMS
2. Amplitude

ifilel -- left HRTF spectral data file

ifiler -- right HRTF spectral data file

Note: Spectral datafiles (based on the MIT HRTF database) should be in the current directory or the SADIR (see hrtfstat documentation)

Performance

abform[] -- input signal array in the B format.

aout[] -– loudspeaker specific output signals.

Example

See test/test_binaural.csd

csound test_binaural.csd --env:SADIR=<path to hrtf folder>

Examples of paths:

Linux: <path to hrtf folder> --> /usr/share/csound/hrtf
OSX: <path to hrtf folder> --> /Library/Frameworks/CsoundLib64.framework/Versions/6.0/Resources/samples

Reference

For more information about the opcode and technical details see:

Pablo Zinemanas, Martín Rocamora and Luis Jure. Improving Csound's Ambisonics decoders. Fifth International Csound Conference – ICSC2019. Italy, 2019.