Appendix B
HOA Decoding
Download the HOA encoded files for acousmatic works of Embodied/Encoded here:
These pieces were composed in my four-channel home studio with additional mixing in Studio 1 at NMH (7.1 channels) and in the 24 speaker dome of Studio 3 at NOTAM. The Harpex decoder works well for any conventional speaker array up to eight channels, specifying AmbiX as the input format (this will discard the higher order components). For each piece, the 3OA file (if included) needs to be mixed with the higher order file on a separate track.
Layouts with more than eight speakers should be decoded with Spat5 in Max or equivalent. Spat 5 has a different default frontal orientation than the IEM plugins used at the encoding stage in Reaper. In this case, a 90-degree rotation is necessary. Both applications use the AmbiX convention and SN3D normalization. A 5OA directions test file (titled "directionsTest_5OA_SN3D.wav") is included in the Brage repository, announcing front, left, right, rear, and top locations. This should be used to ensure that the orientation of the decoder matches that of the encoded file.
For the Being Somewhere concert, I sent my encoded HOA files from Reaper to Max with the BlackHole virtual audio loopback driver. I used In-Phase/Max-Re optimization in Spat5, with a crossover around 500 Hz. Experiment with gain and delay correction for the best imaging with the spat5.align~ object. 3OA stems can be sent to the same decoder or another with a different optimization strategy if enough channels are available.
