Convolver Node

The Convolver Node performs a linear convolution effect, using an impulse response. In simpler – and practical – terms, it adds an environmental effect, or reverb to an audio signal. That is, it makes the audio signal sound as if it was heard in a reverberation room. Or just any large room in general.

A Convolver Node with its various options

For this, you can either bring your own impulse response (e.g. a field recording), or generate them in the Convolver Node itself.

Combine the Convolver Node with the Echo Node to create deep, immersive soundscapes, even from simple sounds. This is a common way to add depth to synth pads, or pretty much any sound that can take the additional reverberation.


How to Use

The Convolver Node needs an input audio signal, to which it can apply the effect, and then output the result. The input audio signal can come from anywhere, as long as it’s audible: an Audio File Node, Oscillator Node, White Noise Node all work.


Inputs

Audio Input

An audio signal to which to add reverb. This should be a stereo or mono signal for best results, as the Convolver Node will downmix it to stereo otherwise.

Amount-Control Input

A control signal to automate the Mix setting, from 0 to 1. You can enable this input from the Node’s properties panel, and is off by default.


Settings

Mix

Sets how much wet to add to the mix. Greater values emphasize the effect.

Impulse response

Sets how the impulse response is created:

  • Generate room impulse response – generates an impulse response by modeling a reverberation room. This mode results in a realistic reverberation feedback, and has plenty of options to customize the result. Ideal to add environmental depth to your sounds.
  • Generate noise – generates an impulse response based on white noise. It results in a soft, immediate reverberation response, which is ideal to quickly add depth to sounds. However, it lacks advanced options to fine-tune the results.
  • From file – use a file as the impulse response, such as a field recording. Supports ttereo (2-channel) and true-matrix (4-channel) impulse responses.

Noise duration

Generate Noise mode only

Sets the duration of the generated impulse response noise, in seconds. Longer values, of course, result in a longer reverb.


Room Size

Room Impulse Response mode only

The basic dimensions of the modeled reverberation room, in meters (width, height, and length). A larger room size results in a longer reverb effect, and a sharper initial reverberation feedback. Note, that the actual dimensions also depend on the room shape setting.

Surface Reflection

Room Impulse Response mode only

How much sound to be reflected from the reverberation room walls, ceiling, and floor. A higher value will result in a longer reverb effect, and a more convoluted audio output. Note, that generating an impulse response, with a very high Surface Reflection value and large room size, can take a long time to complete (up to 10 seconds or even more).

Distance / Delay

Room Impulse Response mode only

How far apart the simulated microphone and simulated audio source are placed. This is a percentage of the room length. Increasing this value will emphasize the reverberation effect, and add a delay before you hear the first reverberation feedback.

Stereo Shift

Room Impulse Response mode only

Moves the simulated microphone, and the simulated sound source around. This adds a stereo effect, turning even simple mono audio sources to rich stereo sounds.

Room Shape

Room Impulse Response mode only – with AudioNodes HD

Controls the reverberation room shape. Lower values produce a box-like room, while higher values produce a longer, hallway-like room instead.

This setting doesn’t affect the main reverberation characteristics – such as the total duration – as much. However, different room shapes provide significantly different results in the audio output.

Noise filter cutoff

Generate Noise mode only – with AudioNodes HD

This setting helps remove some of the hissing from the echoing audio trail.


Outputs

Audio Output

The audio signal with the convolution/reverb effect. This output is always stereo, except when you use a mono impulse response file, with a mono audio input. Extra channels in the input are automatically mixed to stereo.


Technical details

Impulse Responses

Before applying the convolution effect to the connected Audio line, the Convolver Node first normalizes the impulse response file. This uses equal-power normalization.

The Generate noise option creates a full-spectrum stereo white noise with a linear, full-length fade-out.

Performance

Long impulse responses (either generated or file-based) are computationally expensive. Because of this, you should generally use them sparsely. For example, instead of using a Convolver Node multiple times, consider using only 1, after merging your audio using an Add (Audio/Control) Node.


Similar Nodes

  • The Echo Node can also create a similar, reverberating sound
  • You can use the Delay Node to create audio feedback loops