Reverberation

HOLOPHONIX integrates a 3D algorithmic reverberation developed by Ircam's STMS Lab, which integrates both controls over acoustic propagation parameters for virtual sources, and reverberation simulation parameters.

Each spatialization bus is associated with a reverberation bus, that is adapted to the spatialization format.

Understanding the Reverb Engine#

When an acoustic source radiates its sound in a room, its energy propagates across multiple directions before coming back to our ears. We perceive the direct sound first, then the early reflections, and finally the diffuse field.

Reverb Time Structure Graph

The direct sound comes from a unique direction, at the localization of the source. In standard reverberations this is often called the "dry" signal.

The early reflections are caused by the walls close to the source. They come from multiple directions surrounding the source, bringing complementary localization cues, as well as information about the room's size and tone.

Finally, the diffuse field is caused by the multiple and repeated reflections on all the walls of the room. It doesn't bring cues about the source localization, but rather information about the room characteristics such as size and tone. The diffuse field comes from all the directions.

Reverb Time Structure Graph

The diffuse field can be subdivided into two temporal sections: the cluster, followed by the late reverberation. The cluster is composed, much like the early reflections, of multiple delayed signals, progressively blending with the late reverb. Finally comes the late reverberation that is caused by so many reflections over the walls that the delays are not perceptible anymore.

The level ratio between those components also has an impact over the perception of distance in sound localization. With its Slave mode, HOLOPHONIX allows linking to the source distance the following parameters: source delay, direct, early gain and reverb send.

Source Parameters#

Source-related parameters allow adjusting the direct, early and reverb send levels and mute, the early width and slave mode.

Direct#

The 'Direct' section corresponds to the sound coming directly from the source, which is the equivalent of the 'dry' signal for standard reverbs.

Early#

The early reflections are part of what is usually called the 'wet' signal. However, in HOLOPHONIX, because the early reflections are panned around the source position, this parameter is independent of the rest of the reverberation.

Early Width#

The Early Width sets the wideness of the early reflections around the source position. The 30° default value implies that the leftmost early reflection signal will come from -15° at the left of the source, and the rightmost early signal from +15° at the right of the source.

Reverb#

The Reverb Gain sets the level of the signal to be sent to the reverberation bus.

Slave Mode#

The Slave mode allows you to link the desired parameter to the source position. The attenuation is calculated according to the distance from the source to the reference point. The gains decay following an inverse square law.

Bus Parameters#

The reverberation parameters are available along with the settings of the associated bus.

Gain#

The Reverberation Gain allows adjusting its global level.

Mute#

The reverberation integrates a Mute button independent from the bus mute. However, when muting the spatialization bus, the reverb will be automatically muted too, for more convenience. If you want to mute the bus but not the reverberation, you can still unmute the reverb after muting the bus.

EQ#

The reverberation bus includes the same EQ as any audio object.

Room Size#

This setting allows you to change the perception of the simulated space. It will change the delay values computed for the Early, Cluster and Late sections of the reverb.

Reverb Time#

TR0 sets the general reverberation time between 0.1 and 120 seconds. The TRL, TRM, and TRH settings allow adjusting the relative reverberation time per frequency band (Low, Medium, High) between 0.1 and 10 times the global reverberation time. Each band decays at an exponential rate. Use FL and FH to set the crossover frequencies between these three bands.

Air#

The AIR parameter allows you to take into account the air absorption in the reverberation's acoustic simulation.