Specifications

7.1 Channel strip 73
Mute button and smooth fades
*~
dac~
1
dbtorms
100
osc~ 90 sig~
lop~ 1
*
t b f
mute
== 0
fig 7.6: mute
switch
After carefully adjusting a level you may want to temporarily si-
lence a channel without moving the slider. A mute button s olves
this problem. The fader value is stored at the cold inlet of a
*
while the left inlet receives a Boolea n value from a toggle switch.
The usual sense of a mute button is that the channel is silent
when the mute is active, so first the toggle output is inverted.
Some so lutions to zipper noise use
line
or
line~
objects to in-
terpolate the slider values. Using
line
is efficient but somewhat
unsatisfactory since we are still interfacing a message to a sig-
nal and will hear clicks on each block boundary even though the
jumps are smaller. Better is to use
line~
, but this can introduce
corners into the control signal if the slider moves several times
during a fade. A good way to obtain a smo oth fade is to convert
messages to a signal with
sig~
and then low pass filter it with
lop~
.
A cutoff value of 1Hz will ma ke a fade that smoothly adjusts over 1 second.
Panning
Pan is short fo r panorama, meaning a view in all directions. The purpose of a
pan control is to place a mono or point source within a listening panorama. It
should be distinguished from balance which positions a sound alr eady containing
stereo info rmation. The field of an audio panorama is ca lled the image and
with pla in old stereo we are limited to a theoretical image width of 180
◦
. In
practice a narrower width of 120
◦
is used. Some software applications specify
the pan position in degrees, but this is fairly meaningless unless you know
precisely how the loudspeakers are arranged or whether the listener is using
headphones. Mixing a stereo image for anything other than movie theatres is
always a compromise to account for the unknown final listening arrangement.
In movie sound however, the specifications of theatre PA systems are re liable
enough to accurately predict the listeners experience.
Simple linear panner
inlet~ signal inlet control
sig~
*~ *~
sig~ 1
-~
outlet~ left outlet~ right
lop~ 1
fig 7.7: simple panner
In the simplest case a pan control pr ovides for two
sp e akers, left and right. It requires that an increase
on one side has a corresponding decrease on the other.
In the center position the sound is distributed equally
to both loudspeakers. The pan patch in Fig. 7.7 shows
a signal inlet a nd control message inlet at the top
and two signal outlets at the bottom, one for the left
channel and one for the right. Each outlet is preceded
by a multiplier to set the level for that channel, so the
patch is essentially two level co ntrols in one. As with our level control, zipper
noise is removed by converting control messages to a signa l and then smoothing
them with a filter. The resulting control signal, which is in the range 0.0 to