General information

Scroll down to Studio 114 for specifics.

Ambisonics in KMH studios and Lilla salen

About ambisonics

The general idea behind using ambisonics for difusing sounds in a space is to, in the first stage, encode an audio signal to a representation of a sound field - a B-format signal. This B-format signal is idependent of whatever speaker array the signal will later be diffused on. In the second stage the B-format signal is decoded to the layout of a particular speaker array. In between these two stages a number of transformations may be applied, but the sound source specification may conveniently be specified in the encoder.

In principle, any kind of encoder may be combined with any kind of decoder provided that the same channel order is used. Among the encoders (VST) that work with the decoders presented here are Ambix and IEM Plugin suite. Using these makes it simple to automate panning in a DAW such as Reaper.

About the compiled decoders

All decoders use ACN channel order (see Component order) and SN3D normalization (see Normalisation) and are dual-band, max-rE/rV.

• A guide to the file names

  For efficiency file names are composed of the following parts

  1. The space (for Lilla Salen this is KMHLS_AE)
  2. Speaker configuration (Full or Normal where the former in 108/118 and 114 means the center speaker is included, and in Lilla Salen it refers to the 45.4 setup)
  3. Order (e.g. 7H7P)
  4. Redundant speaker configuration (full, but only in certain cases for Lilla Salen)
  5. Finally, a number depicting the type of decoder according to the following codes:

  • (1) AllRad mixed order (4/3)

    Mixed order ambisonics decoder.

  • (2) Decoding with the pseudo-inverse, even-energy

    Pinv decoders in 1st, 3rd order with even-energy for inversion variants.

    The higher order decoders in pseudo-inverse do not work well, so do not try those above 3rd order.

  • (3) Decoding with the pseudo-inverse, mode-matching

    Pinv decoders in 1st, 3rd order, mode-matching for inversion variants. This has been removed from the repository.

  • (4) Same as (2) but with a blend coefficient for inversion variants (energy limited/mode matching 50%)

    1st and 3rd and 6th order.

    The higher order decoders in pseudo-inverse do not work well, so do not try those above 3rd order - though sixth order has provecd useful.

  • (5) Spherical slepian decoders

    SSF decoders in 1st, 3rd and 6th order (6th order is here only as VST, but I can compile the other formats if needed.)

  • (6) All-round decoders

    AllRAD decoders in 1st, 3rd, 5th and 7th order.

• Ouput formats

  In the directory of each decoder there are four subdirectories:

  • ambix: contains the decoder matrix for the ambix VST-plugin for certain settings.
  • bin: contains all other decoders
  • doc: documentation, a bare minimal (but a more comprehensive documentation can be built from the source, check the individual Makefiles for each compilere)
  • src: the faust sources for the decoders

  The binaries are prepared in six different formats:

  1. a jack application (start from commandline: $ KMHLS_Dome_4h3v_normal_1)
  2. a double clickable CoreAudio application
  3. a 'max' directory with Max/MSP objects (as package with help files to be put in ~/Documents/Max 7/Packages)
  4. a 'pd' direcory (bang left most input to get parameter names)
  5. a 'sc' directory with SuperCollider classes (put all .sc and .scx in ~/Library/Application Support/SuperCollider/Extensions , the supernova files are of course optional)
  6. an 'ambix' directory with Ambix config file

  • Install on your system

    You may simply move the decoders you want to use to the right locations on your system. They are compiled and ready to be used in the repository. As a convenience one may run the corresponding install scripts in the Makefile for the decoders to install them in your default directory:

    1. Open a terminal (such as Terminal.app)
    2. At the prompt type $ cd and drag one of the directories, say 'KMHLS_AE_normal_6' of your downloaded repository onto the terminal and press enter.
    3. Enter $ make maxinstall at the prompt and press enter.

    The last step can be made for scinstall, vstinstall and pdinstall

    Note that to create a Max/MSP compatible package you may have to run maxinstall and have the reslevant dependencies resolved. Else, contact me!

• Component order

  The component order for the input to the decoder follows the ACN (Ambisonics Channel Number) standard according to the table below (for third order):

  			0
  		1	2	3
  	4	5	6	7	8
  9	10	11	12	13	13	15

  Or: W Y Z X V T R S U Q O M K L N P

• Normalisation

  The decoder is using SN3D normalisation. With SN3D normalisation no component will exceed the peak value of the 0th order component.

• Compiling the decoders

  This is only if you wish to tweak the settings in any way. All scripts needed for the compilation is in a speparate GitHub repository that may be found here: In order to compile the decoders there are a number of dependencies that need to be resolved:

  • ADT (Ambisoncs Decoder Toolkit)

  • Faust

  • VST SDK

  • Pure Data

  • Max MSP SDK

  • Links to Supercollider classes

  • Running Makefile scripts for ADT

    Run the following for each function that needs to be compiled for lilla salen (108_all and 114_all for the studios):

    $ make ls_all function=6

    Note that for fuction 2 & 4 only orders up to 3 are usable.

    The decoding matrices end up in a directory above your current directory named 'decoders'. Move into that directory with the following command:

    $ cd ../decoders

    With the decoding matrices calculated the binary decoders for all orders can be compiled by

    $ make -k target=all all

    The target can be either of [all,sc,max,pd,vst]. Following this step the binaries can be installed (to install only one target, use that as the argument for 'target'.:

    $ make -k target=install all

Studio 114

Specific info for 114

Output

Generally in ambisonics a speaker array is organized in circles. Due to the ambition to accomodate many different surround sound techniques this is not the case in Studio 114. For this reason some care needs to be taken to make sure that the right ambisonic channel is coming out of the correct speaker. There are two general version of the decoder for KMH114. KMH114_C is equal to KMH114 except that the first also includes the center speaker which may, or may not, be preferable.

Channel output mapping

In principle the output of the decoders should be mapped to the speakers according to the following table:

Decoder output	KMH114	KMH114\_C
1	1 (L)	1 (L)
2	2 (R)	2 (R)
3	5 (LSR)	3 (C)
4	6 (RSR)	5 (LSR)
5	7 (LSF)	6 (RSR)
6	8 (RSF)	7 (LSF)
7	9 (RL)	8 (RSF)
8	10 (RR)	9 (RL)
9	11 (ULF)	10 (RR)
10	12 (URF)	11 (ULF)
11	13 (URL)	12 (URF)
12	14 (URR)	13 (URL)
13	15 (VOG)	14 (URR)
14	-	15 (VOG)

L, R, LSR, RSR, LSF, RSF, RL, RR, ULF, URF, URL, URR, VOG

Utility program

For studios 108 and 114 there is a small utitlity program that wraps your channels around. For 114, this means that you can insert KMH114_channel_map after your decoder and your channels will come out in the right order for a linear routing on the SSL (1 -> 1, 2 -> 2, etc)

Speaker positions

Speaker index is counted linearly clockwise from FL. Subs are skipped.

ndx	azimuth	elevation	distance
1	24.6	0	3.26
2	0	0	3.27
3	-26.34	0	3.3
4	-58.7	0	3.35
5	-106	0	3.27
6	-129.35	0	3.364
7	129.35	0	3.376
8	106	0	3.262
9	58.7	0	3.296
10	45	18	3.02
11	-45	18	3.02
12	-135	18	3.05
13	135	18	3.02
14	0	90	1.60

Spat

• Center included

  A setup file for the current speaker arrangments in Studio 114 according to Speaker positions for use with the Ircam spat package.

  In Max/MSP (Spat), make an object: [spat.viewer @numspeakers 15 @showlistener 1 @viewpoint top @width 1200 @height 600] and send it the following in a message:

  speakers aed
  24.6 12.910417 4.61 0 12.910417 4.61 -26.34 12.910417 4.61 -58.7 12.910417 4.61 -106 12.910417 4.61 -129.35 12.910417 4.61 129.35 12.910417 4.61 106 12.910417 4.61 58.7 12.910417 4.61 45 12.910417 4.61 -45 12.910417 4.61 -135 12.910417 4.61 135 12.910417 4.61 0 12.910417 4.61
  

IEMAllRad

• JSON files for speaker position

  A setup file for the IEM AllRad decoder may be found in the IEM directory of the repository. Remember to re-calculate the decoding matrix if you load a new setting or change the setup (see the screenshot).

  

Panoramix

The current speaker arrangments in Studio 114 according to the table in Speaker positions may be used with the Ircam Panoramix package. The two files below may be imported in a Panoramix HOA bus:

The following file may be loaded in a HOA bus track (See fig:hoabus) in panormaix by selecting the text below, clicking the spekers... button and click paste in the upper left corner of the newly opened window.