E4L B Format Convolution Reverb
The E4L B-Format Convolution Reverb is an innovative spatial audio effect which uses multi-channel convolution to simulate reverberation in a 3D space based upon a B-format impulse response. This devices operates in the Ambisonics domain and must be placed after a spatialization device on the same chain, such as an E4L Source Panner.
The W, X, Y and Z buttons can be used to select individual impulse response WAV files for each of the HOA channels. Alternatively, impulse response files may be dragged and dropped onto the sample bins, or a folder containing 4 impulse responses may be dragged and dropped.
The behavior of the impulse response may be modified using various controls. Size scales the impulse response to shorten or lengthen the reverberation time. Rotate controls modify the orientation of the impulse response by mutating the Yaw, Pitch and Roll of the impulse response.
In natural room acoustics, as a sound source moves away from the listener, the gain of the direct signal and early reflections of the source are attenuated, while the late reverberation gain remains stable. To create a spatially directional reverberation effect, the E4L B-Format Convolution Reverb device can be used in combination with an E4L Source Panner device on the same track. The E4L Source Panner internally applies distance attenuation for the direct signal, and when the E4L B-Format Convolution Reverb device's Dist mode is set to Lock, the distance metadata from the E4L Source Panner is used to compensate for the distance attenuation to keep the late reverberation level stable. When the Dist mode is set to Free, the late reverberation does not look for the panner distance information, and in this mode the late reverberation gain will change with the gain of the input signal. For example, you might want to use Free mode for cases were you are not using an E4L Source Panner, but some other kind of source that does not apply distance attenuation.
There are four stages of EQ filtering applied. The first stage applies to the Dry signal. The second stage applies to the Wet signal, before it is convolved. The third stage is applied to the result of the Early convolutions. And the fourth and final stage is applied to the result of the Late reflections.
The Dry/Wet control adjusts the relative balance of the Dry and Wet signal chains, and there are additional gain controls applied to adjust the level of the Early and Late stages.
The diagram below indicates the DSP signal routing:
Some B-format impulse responses, separated into WXYZ mono components are available: B-format impulse responses