HOA Tutorial Exercise 06:
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HOA Tutorial Exercise 06
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simple transformations of the B-format, mirroring and rotation.

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After learning how to play back HOA soundfiles, the examples below demonstarte how to use the classes

in order to manipulate the HOA B-format. For the details of the mirroring and rotation transformations please refer to: [1] M. Kronlachner, “Spatial Transformations for the Alteration of Ambisonic Recordings,” Graz University Of Technology, Austria, 2014 p.46-47.

The x,y,z (roll, pitch, yaw) rotator of the HOA scene uses the for the matrix definition from [2] with implentation according to [1] for details about the corrections in the implementation see underlying Faust code by Pierre Lecomte: https://github.com/sekisushai/ambitools/blob/master/Faust/src/hoa_rotator.dsp[2] J. Ivanic and K. Ruedenberg, “Rotation matrices for real spherical harmonics. Direct determination by recursion,” J. Phys. Chem., vol. 100, no. 15, pp. 6342–6347, 1996.

In case you have not done so yet: let's start the sound server, which we configure first to get more audio buses and to have 36 output channels.

Start the oscilloscope showing all the channels for the selected order of the b-format.

We will load a very short sound file that we loop so that we can observe the soundfield transformations:

Let's make a node that can play back the 3rd order HOA sound file.

Here we use HOATransMirror to simply mirror the sound field along the x, y, and z axis.

Then we make the decoder as before.

And we connect the NodeProxies to hear something

Now we can flip the sound field:

Here we have an example with HOATransRotateAz where we rotate the sound scene around the z-axis.

Here we have an example with HOATransRotateXYZ where we rotate the sound scene around all three axis.

Previous: Exercise_05_HOA_b_format_file_playback

Next: Exercise_07_HOA_beamforming