The program can also calculate room reflections,
when a room is defined by the user through the
position of four walls of a rectangular room, an
absorption factor and the order of calculation. The
calculations are done with the mirror image source
model (see also Berkhout 1988).
Though with WFS one can in principle also
create virtual sources in front of the loudspeaker
array, this was not yet implemented in the current
version. It will however be implemented in a future
version.
4.1 Sound source definition
The user can define various sources, each with
their own characteristics. A source in this context is
the virtual source from which sound emanates in
space, whose spatial parameters can be given by the
user.
For each source, the user can set the type of
source (a point source having a specific location or a
plane wave having only a direction), whether it is
moving or stationary, its location or angle, the sound
input channel at which the sound will be supplied
and in the case of a point source, whether reflections
have to be calculated or not. If reflections have to be
calculated, room characteristics can be defined
(these can be different for each source). In the case
of a moving source, one can define a path through
space and choose to let the movement loop along the
path. In figure 3 a screenshot of the source and path
definition dialog is given.
After supplying all information and storing it, the
user can get two overviews: a general overview in a
list, with some of the most important parameters for
each source, and a graphical overview showing the
paths of the sources through space (figure 4); one
can indicate of which sources the path is shown. It is
also possible to play a movie to get an impression of
the movement in realtime.
For the movement of the sounds, one can set the
number of breakpoints along the path and a fade
order. A breakpoint is an intermediary point on a
path; movement is created by switching from one
breakpoint to another. By using a fade between
succesive breakpoints, the movement can become
smoother and possible clicks in playback can
become softer. The user can choose to let the
amount of breakpoints on each segment be
calculated automatically. In that case, the program
uses a total of 40 breakpoints per source and divides
these over the segments of the path, depending on
the length of the segment and of the path and on the
time interval.
Figure 4. Screenshot of the graphical overview of the source path. The
numbers at the points between segments indicate the departure (dark) and
arrival (light) times. The dots in between the path and the reference point
are indicating the loudspeaker array.