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-----------------------------------------------------------------------------------
Copyright (C) 2004-2007 Fons Adriaensen
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
-----------------------------------------------------------------------------------
I'm using these mostly with Ardour (see below for some hints),
but you could use any of these plugins as well in a softsynth
such as Om or AMS.
All the plugins use first order B-format. B-format signals have
four channels named W, X, Y, Z and always in that order.
--------------------------------------------
AMB-plugins-0.3.0 Released 2007.08.27
--------------------------------------------
* Two new plugins added, both second order horizontal
and first order vertical (i.e. six channels).
1979 2nd order Mono panner
1980 2nd order Rotator
* New name scheme introduced, using two numbers:
a,b means horizontal order 'a', vertical order 'b'.
* Plugins are now organised in two files:
ambisonic1.so : first order (6 plugins)
ambisonic2.so : second order (2 plugins)
The install target in the Makefile will remove any
older versions. If you have saved host configurations
(e.g. Ardour sessions) using any of these plugins you
may have to remove and re-insert them.
--------------------------------------------
AMB-plugins-0.1.0 Released 2006.07.16
--------------------------------------------
Main feature of this release are the improved decoders.
These now have optional phase-aligned shelf filters that
enable to have a different decoding matrix for low and
high frequencies. This is explained in more detail below.
(A similar feature was present in older releases, but the
implementation was not entirely correct and the filters
used were not phase aligned).
NOTE: if you are using the decoders in existing patches
or sessions you may have to remove and re-insert them
as the number and type of control ports has changed.
The panner and rotation plugins are the same as in the
previous release (0.0.2).
B-format to square decoder
--------------------------
B-format to hexagon decoder
---------------------------
B-format to cube decoder
------------------------
Decode a first order B-format to signals for a square, regular
hexagon or cube speaker layout. All plugins have W,X,Y,Z inputs
but Z is not used for the sqaure and hexagon versions. All three
decoders share the same controls:
Front: This switch selects one of two possible layouts.
When 'off' the decoder assumes the usual setup
with left and right front speakers. The first
output is the left front speaker, then going
clockwise around the circle.
When 'on', the decoder assumes a rotated layout
with a single centre front and back speaker.
The first output is centre front in this case.
Distance: This should be used to compensate for the proximity
effect of the speakers in a small (e.g. control
room) layout. The parameter is the distance of the
listener to the speakers [1 .. 30m]. It controls a
1st order highpass filter on the velocity components.
Shelf, HF XYZ gain, LF XYZ gain, Shelf frequency:
These control the relative gain of the first (XYZ)
relative to the zero order (W) components. With the
Shelf switch 'off', the same value is used for all
frequencies and controlled by the HF XYZ gain value.
LF XYZ gain and Shelf frequency are not used in that
case. With Shelf switched 'on', separate control for
low and high frequencies is enabled. The Shelf frequency
parameter controls the transition frequency between the
two regions.
The two gain controls work as follows:
At the minimum setting (1), the decoding is such that
there will never be any antiphase signals for a single
source. This "in-phase" setting is usually recommended
for large (auditorium) setups where a larger "sweet
spot" is desired.
At the centre value of the gain controls (sqrt(2) for
horizontal and sqrt(3) for the cube decoder), the
result wil be the "max rE" decoding which is optimal
at high frequencies for small and medium size setups.
For the maximum value of the gain controls (2 for 2D
and 3 for 3D), the resulting decoding is the "max rV"
one which is optimal for low frequencies but will give
a smaller "sweet spot".
For a small (control room) setup for a single listener
the normal settings would be max rE for HF and max rV
for LF, together with the correct distance compensation.
Mono to B format panner
-----------------------
Pan a mono source to a first order B-format. Controls are:
Elevation: Vertical component of the direction [-90 .. +90].
Azimuth: Horizontal direction, [-180 .. +180].
Positive values are to the right. Back is +/-180.
Changes to the control ports are 'smoothed' over one period.
The interpolation is done not on the input values but on the
direction vectors computed from them. This means for example
that if consecutive azimuth inputs are -170, +170, the result
will be a smooth transition through the back direction, just
as -10, +10 would interpolate via the front direction.
Stereo to B format panner
-------------------------
Pan a stereo source to a first order B-format. Controls are:
Elevation: Vertical component of the direction [-90 .. +90].
Azimuth: Horizontal direction of the center of the stereo
image, [-180 .. +180]. Positive values are to the
right. Back is +/-180.
Width: Horizontal width of the stereo image [-90 .. +90].
Negative values give a mirror image.
As for the mono panner, the control port values are inter-
polated over one period, and there is no discontinuity at
+/- 180 azimuth, provided you give the right inputs.
Horizontal rotator
------------------
Rotate a first order B-format signal around the Z axis. there
is just one control:
Angle: Rotation angle [-180 .. +180], positive is to the
right.
The rotation is smoothed in the same way as the for the two
panners.
-----------------------------
Using AMB plugins with Ardour
-----------------------------
Ardour is not aware of encoded formats such as B-format, and therefore
using them requires some attention. Some hints:
* Switch ON the option 'Use plugins while recording', and switch OFF
the option 'Auto connect new tracks'. The latter is not saved in the
session file, so watch out when reloading a session. The effects of
the automatic connections can sometimes be quite confusing when using
a mix of mono, stereo and B-format tracks and strips.
* All the plugins should normally be used post-fader. First create
the strip's inputs (1, 2 or 4) and outputs (4, 6 or 8). Then disable
Ardour's multichannel panner, and only then insert and activate the
plugin.
* Apart from the 'auditioner', Ardour's mixer has no dedicated
modules for monitoring, and hence no place to 'insert' a decoder.
A practical solution is to create a 'monitoring' strip (not a
'track' but a 'bus'). Insert the required decoder post-fader,
connect the inputs to your B-format 'master' strip, and the outputs
to the inputs of your monitoring system. Also connect the 'auditioner'
outputs to the same destination as the first two decoder outputs.
Apart from these, there should normally not be any other signals
going directly to the speakers.
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