ER-301/Exact Convolution

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  • FIR filter
  • (short) Reverbs
  • Multi-tap delay


This unit convolves the input signal with an impulse response (IR) loaded into the unit via an audio file. The maximum number of samples that this unit will actually use from the audio file is:

  • 48kHz: 48,000 samples (or 1s)
  • 96kHz: 24,000 samples (or 0.25s)

This unit is implemented using the UPOLS (Uniform Partitioned Overlap-Save) algorithm, p. 110 which is much more efficient than naive convolution.

However, it is still a CPU-heavy operation. For example, with the 48kHz firmware, an 800ms impulse response will consume slightly more than 50% of the available CPU cycles. Use with caution.

Special Menu Operations

Select from Card

Load an impulse response (as a WAV file) directly from the front SD card. The selected WAV file is loaded into the Sample Pool and attached to the unit.

Select from Pool

Selects the impulse response from the Sample Pool.



Control Type Has Sub-chain? Sub-chain Parameters Fader Scale
Gain/Bias yes gain (-3 to 3)

bias (0 to 1)


This parameter controls the amount of the input signal and of the affected signal which is passed to the output. A value of 1 (i.e. 100% wet) means you will only hear the affected signal. A value of 0 (i.e. 100% dry) means you will only hear the signal received at the unit's input. However, the cross-fade curve is not linear but rather lifted to counteract the tendency for loudness to dip in the center of a linear cross-fade curve. The actual cross-fade curve looks like this: