Ambisonics Reverb

There are a few different ways to manage reverb effects in an ambisonics mix.

The Easy Way

The first and simplest is to use a separate reverb plugin on each strip before the ambisonics panning plugin, then all of the B-Format outputs can be routed into one Master strip that includes an ambisonics decoder plugin.

The advantage of this method is that it is simple, that you can use different settings (or even completely different reverb plugins) for each instrument. The disadvantage is that each of those reverb plugins uses some (usually very small) amount of CPU time and the effect may sound more artificial. (it is, in effect, like placing an soundfield microphone in the middle of a room in which have been positioned many loudspeakers, each connected to a separate reverb unit, with XLR cables leading to microphones in other rooms, where each instrument is in a private, soundproof booth).

The Slightly Less Easy Way

Alternatively, one can use a single Ambisonics reverb (such as Fons Adriaensen's zita-rev1) with it's Dry/Wet control set all the way to Wet, and route the post-fader, pre-panner signals from the various instruments (via the Aux module) into it. The level of gain on the Aux output effectively controls the relative amount of reverb for each instrument. The output of the reverb can be routed through another mixer strip before going into the Master inputs. The gain on this strip (lets call it Reverb) will then control the group reverb level of all instruments.

The reason this works is that only the first couple of dozen milliseconds of an impulse are important for spatial perception. The dry signal continues through the ambisonics panner and then to the Master strip, while the aux send directs some fraction of the pre-panner signal (lacking any spatialization information) into the reverb (and then also into the master strip). Since the reverb is set to 100% wet signal, its output contains only the reverberations, which arrive after a slight delay (dependent on reverb delay/roomsize settings)--by this time the listener has already decided where the sound source is located.

The image below illustrates the JACK graph of such a mix.

And here's what the same configuration looks like in Non Mixer


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