FXAlg #12: Panaural Room
Algorithm Reference-21
FXAlg #12: Panaural Room
Room reverberation algorithm
Allocation Units:
3
The Panaural Room reverberation is implemented using a special network arrangement of many delay lines that
guarantees colorless sound. The reverberator is inherently stereo with each input injected into the ÒroomÓ at
multiple locations. The signals entering the reverberator first pass through a shelving bass equalizer with a range
of +/-15dB. To shorten the decay time of high frequencies relative to mid frequencies, lowpass filters controlled by
HF Damping are distributed throughout the network. Room Size scales all the delay times of the network (but not
the Pre Dly or Build Time), to change the simulated room dimension over a range of 1 to 16m. Decay Time varies
the feedback gains to achieve decay times from 0.5 to 100 seconds. The Room Size and Decay Time controls are
interlocked so that a chosen Decay Time will be maintained while Room Size is varied. A two-input stereo mixer,
controlled by Wet/Dry and Out Gain, feeds the output.
Simplified block diagram of Panaural Room.
The duration and spacing of the early reflections are influenced by Room Size and Build Time, while the number
and relative loudness of the individual reflections are influenced by Build Env. When Build Env is near 0 or 100%,
fewer reflections are created. The maximum number of important early reflections, 13, is achieved at a setting of
50%.
To get control over the growth of reverberation, the left and right inputs each are passed through an ÒinjectorÓ that
can extend the source before it drives the reverberator. Only when Build Env is set to 0% is the reverberator driven
in pure stereo by the pure dry signal. For settings of Build Env greater than 0%, the reverberator is fed multiple
times. Build Env controls the injector so that the reverberation begins abruptly (0%), builds immediately to a
sustained level (50%), or builds gradually to a maximum (100%). Build Time varies the injection length over a range
of 0 to 500ms. At a Build Time of 0ms, there is no extension of the build time. In this case, the Build Env control
adjusts the density of the reverberation, with maximum density at a setting of 50%. In addition to the two build
controls, there is an overall Pre Dly control that can delay the entire reverberation process by up to 500ms.
PreDelay
PreDelay
Reverb
Dry
Dry
Out Gain
L Output
R Output
L Input
R Input
Wet
