Reality and Secrets no. 2: Technical notes and performance information

Reality and Secrets no.2 is a full 3D higher-order ambisonics (HOA) composition. It is encoded in a hybrid format to take advantage of the features inherent in different approaches to the encoding and decoding of ambisonics spatial information.

The master of Reality and Secrets no.2 includes the following versions:

Encoded sources:
• Encoded full 3D for hemispherical decoding, or for other accurate 3D loudspeaker placements.
• Encoded horizontal 3D for horizontal loudspeaker arrays.

Pre-decoded sources:
• Stereo for two loudspeakers
• Binaural for headphones
• Quad (plus sub bass)
• 5.1

Main version: 3D for hemispherical decoding or other accurate 3D loudspeaker placements.

This version provides optimal decoding for most full 3D situations both at present and for some time into the foreseeable future (more about the method can be found in: Barrett, N. Kernel Expansion: a three-dimensional spatial composition combining different ambisonics spatialisation techniques. (2010). Proceedings from the Second International Symposium on Ambisonics and Spherical Acoustics, Paris.)

Materials:

• Four layers of hybrid horizontal N3D coefficient weighting 5th-order ambisonics (5,1 = 5th order horizontal plus first order full 3D):
RS_no2_n3d_layerbottomEQ.aiff
RS_no2_n3d_layermidEQ.aiff
RS_no2_n3d_layertopEQ.aiff
RS_no2_n3d_layerfullEQ.aiff

• One layer of full 3D FuMa coefficient 1st-order ambisonics:
RS_no2_bformat_layerEQ.aif

The channel ordering in the N3D 5th-order ambisonics follows the ACN convention (see http://ambisonics.ch/standards/channels/):
N3D (5,1) = 0 , 1 , 2 , 3 , 4 , 8 , 9 , 15 , 16 , 24 , 25 , 35 (which is WYZXVUQP .... etc.)

The channel ordering in the 3D FuMa 1st-order follows the standard:
FuMa (1,1) = WXYZ

Decoding and performance of full 3D:

The five layers are distributed with vertical displacement:

• HOA layer 1 (RS_no2_n3d_layerbottomEQ.aiff): for bottom ring of loudspeakers (the main ring just above audience head height).
• HOA layer 2 (RS_no2_n3d_layermidEQ.aiff): for mid ring of loudspeakers.
• HOA layer 3 (RS_no2_n3d_layertopEQ.aiff): for upper ring of loudspeakers.
• HOA layer 4 (RS_no2_n3d_layerfullEQ.aiff): full 3D decoded over all loudspeakers.
• FuMa layer 5 (RS_no2_bformat_layerEQ.aif): full 3D decoded over all loudspeakers.

Each layer requires a different instance of the decoder set to the correct decoding order.
• The first three layers can be decoded with a standard decoder with Max rE / rV (such and Ambdec) or without (such as ICST decoder).
• The two full 3D layers (layers 4 and 5) should be decoded with Harpex.
Note that layer 4 is encoded in 5th-order N3D. This is to allow for more advanced future decoders. For now, decode just the first four channels with Harpex. Remember to convert from N3D to FuMa channel order and co-efficient weighting.

After decoding, the relative volume of each layer needs to be set. If the decoder normalises the output, this is done via a simple dB multiplication in relation to loudspeaker numbers. Here is an example for a hemispherical loudspeaker array where:
Speaker layer-1 contains 12 loudspeakers
Speaker layer-2 contains 10 loudspeakers
Speaker layer-3 contains 6 loudspeakers

Decoded gains will be:
HOA layer 1 decoded with ICST as 5th-order over 12 loudspeakers = -6dB
HOA layer 2 decoded with ICST as 4th-order over 10 loudspeakers = -4.4dB
HOA layer 3 decoded with ICST as 2nd-order over 6 loudspeakers = 0dB
HOA layer 4: full 3D decoded with Harpex 1st-order over all loudspeakers = +3.5dB
FuMa layer 5: full 3D decoded with Harpex over all loudspeakers = +3.5dB

Once set, the over all volume can be adjusted by the master fader.

A mono subbass track is provided: R_and_S_no2_sub_for_encoded.aif

In addition test files are provided:
n3d-5th_order_noise_test.aif
FuMa_noise_w_height_testfile.aif

These test files are decoded and gain compensated via the same method as above. The audible result should be an equal volume rotating noise. It may be necessary to increase or decrease the gain of layer 5 depending on room acoustics and Harpex version. The test file can be used as calibration.

NOTE: At present I suggest contacting me for specific decodings. In the future I will be able to include decoding software (copy protection currently prevents this).

Decoders
Harpex: http://harpex.net/
ICST: http://www.icst.net/research/downloads/ambisonics-externals-for-maxmsp/
Ambdec: http://www.kokkinizita.net/linuxaudio/downloads/index.html (runs on Intel OSX)

Horizontal version

Use this version for horizontal loudspeaker arrays.

Materials:

• One layer hybrid horizontal N3D 5th-order ambisonics (5,1 = 5th order horizontal plus first order full 3D): RS_no2_n3d_layermixEQ.aiff
• One layer full 3D FuMa 1st-order ambisonics: RS_no2_bformat_layerEQ.aif
• One 1st-order FuMa downmix of all materials: R&S_no2_bformat_mixEQ.aif

Decoding and performance of horizontal version:

• For decoding to 8 or less horizontal loudspeakers use the single 1st-order FuMa R&S_no2_bformat_mixEQ.aif decoded with Harpex.
• For decoding to 10 loudspeakers use a 4th-order standard decoder for the N3D file RS_no2_n3d_layermixEQ.aiff and Harpex for the 1st order FuMa file RS_no2_bformat_layerEQ.aif Test files provided for full 3D can be used. (Gain compensation applies: e.g. for a 10 speaker array the Harpex decoded file needs +8dB gain in relation to the ICST decoder).
• For decoding to 12+ loudspeakers use a 5th-order standard decoder for the N3D file RS_no2_n3d_layermixEQ.aiff and Harpex for the 1st order FuMa file RS_no2_bformat_layerEQ.aif (gain compensation applies).

For all loudspeaker decodings a mono subbass track is included: R_and_S_no2_sub_for_encoded.aif

Pre-decoded versions:

Quad decoding: R-andS_2_quad_EQ.aif
Channel routing (equal distance from centre, angles -45/45/135/-135)

1_2
4_3

5.0 decoding: R_and_S_no2_5_EQ_comp.aif

Channel routing (equal distance from centre, angles -30/0/30/110/-110)

___2___
_1___3

5_____4

For all loudspeaker decodings a mono subbass track is included: R_and_S_no2_sub_for_quad_and_5.aif

Hrtf / binuaral for headphones: R&S_no2_hrtf_kemar1_horizEQcomp.aif

Stereo loudspeaker decoding to wide XY characteristic: R&S_no2_stereo_XY180EQcomp.aif