Temporal Erosion — User Guide

Poisson-IR convolution reverb with logarithmic decay, bounded Gaussian roughening and Hann-band spectral shaping.

Author: Shai Cohen Affiliation: Department of Music, Bar-Ilan University, Israel Version: 0.4.1 (2026) License: MIT License Repo: https://github.com/ShaiCohen-ops/Praat-plugin_AudioTools

Contents:

What this does Quick start Presets Parameters IR construction IR energy, duration and level Visualization Output

What this does

Temporal Erosion is a convolution reverb built from a dense Poisson impulse response. The IR is shaped by a logarithmic decay envelope, sample-wise Gaussian amplitude roughening, and a Hann spectral window. The logarithmic envelope falls quickly at the beginning and progressively more slowly toward the end, while the random multiplier gives the IR an eroded, irregular surface.

What is convolution reverb? A convolution reverb applies an impulse response (IR) to a source. Every impulse in the IR produces a delayed, weighted contribution from the source. Here the IR is generated algorithmically rather than measured from a physical room.

For stereo input, left and right IRs are generated separately with slightly different duration, Poisson density, erosion strength and filter bands. A single common IR-energy gain is then applied to both sides to preserve their relative balance.

Quick start

Select exactly one mono or stereo Sound.
Run Temporal_Erosion.praat.
Choose Subtle, Medium, Heavy, Extreme, or Custom.
Use Poisson_density for event density and Erosion_randomness for sample-wise amplitude roughness.
Set the Hann filter band with Low_cutoff_Hz, High_cutoff_Hz and Smoothing_Hz.
Set wet/dry and run.

Presets

Preset	Tail	IR duration	Density	Band	Smoothing	Erosion σ	Fade	Wet
Subtle Erosion	2.0 s	3.0 s	1500/s	120–7000 Hz	80 Hz	0.20	1.0 s	35%
Medium Erosion	3.0 s	5.0 s	2500/s	100–8000 Hz	100 Hz	0.30	1.2 s	50%
Heavy Erosion	4.0 s	7.0 s	4000/s	80–9000 Hz	120 Hz	0.40	1.5 s	65%
Extreme Erosion	5.0 s	10.0 s	6000/s	60–10000 Hz	150 Hz	0.50	2.0 s	80%
Custom	Uses the values entered in the form.

Parameters

Parameter	Default	Meaning
Tail_duration_s	3.0 s	Requested output tail beyond the dry source.
Impulse_duration_s	5.0 s	Duration of the left/mono Poisson IR before the output is mapped into the fixed output canvas.
Poisson_density	2500/s	Average event rate of the left/mono Poisson process.
Low_cutoff_Hz / High_cutoff_Hz	100 / 8000 Hz	Requested Hann pass band. The high cutoff is limited to 95% of Nyquist.
Smoothing_Hz	100 Hz	Transition width, automatically limited so transitions remain inside the usable spectrum.
Erosion_randomness	0.30	Standard deviation of the Gaussian sample-wise multiplier. Negative values are clamped to zero.
Wet_dry_percent	50%	Linear wet/dry mix.
Fadeout_duration_s	1.2 s	Cosine fade on the wet tail only, limited to the requested tail duration.
Draw_visualization	yes	Draw the dry/output waveforms, decay law, effective spectral window and summary.
Play_result	yes	Play the resulting Sound when processing finishes.

IR construction

normalized IR time: τ = (x - xmin) / (xmax - xmin) log envelope: E(τ) = 1 - log10(1 + 9τ) roughness: R = clamp(randomGauss(1, σ), 0, 2) IR sample: pulseTrain × E(τ) × R

The envelope starts at 1 and reaches exactly 0 at the IR end. The roughness multiplier is independently generated sample by sample and bounded to 0–2. The result then passes through a Hann band filter.

For stereo, the right IR is deliberately decorrelated: duration = 0.96×, density = 0.92×, erosion sigma = 1.17×, the lower cutoff is shifted upward, the upper cutoff slightly downward, and smoothing is reduced when possible.

Randomness: no seed is set, so the Poisson events and Gaussian erosion pattern change between runs.

IR energy, duration and level

Before convolution, the IR is normalized by discrete energy, not by peak. In stereo, the script measures both IR energies and applies one common gain based on the larger energy, preserving left/right balance.

Supported input: mono or stereo only.
Output channels: same as the input.
Sample rate: preserved.
Time origin: nonzero-wet processing renders a new output canvas beginning at 0 s while reading the dry source with its original start time accounted for. The 0% wet fast path is a direct copy and preserves the original time domain.
Nonzero wet: the result is rendered into a fixed canvas of source duration + Tail_duration_s; longer convolution material is trimmed and shorter material is zero-padded.
0% wet: true dry-only fast path—an unchanged copy at the original duration, with no added tail.
Peak safety: after nonzero-wet processing, the result is attenuated to 0.98 only if its peak exceeds 0.98.

Visualization

The display includes dry and output waveforms, a plot of the exact logarithmic decay law, and the effective Hann spectral window. For stereo, the right-channel spectral window is shown as a separate dashed curve. The summary reports IR duration, tail, density, erosion sigma, effective filter band, fade and output duration.

Output

The result is named <source>_erosion_<preset> with Custom, Subtle, Medium, Heavy or Extreme.