Ribbon Shimmer — v0.2 User Guide

Lush reverb effect with exponentially‑spaced delays and high‑frequency enhancement. Delay times follow: delay[k] = min_delay × (max_delay / min_delay)^(k/N), creating dense early reflections that thin out over time. HF sparkle via differentiation adds “air”. Polarity alternation creates rich phase texture.

Author: Shai Cohen Affiliation: Department of Music, Bar‑Ilan University, Israel Version: 0.2 (2025) – Stereo, wet/dry, visualisation License: MIT License Repo: GitHub

Contents:

What it does Quick start Presets (4 archetypes) The exponential delay law Parameters Visualization FAQ / troubleshooting

What this does

Ribbon Shimmer creates a lush, ribbon‑like reverb by generating a dense series of echoes with exponential delay spacing – delays grow exponentially from a minimum to a maximum, creating a natural‑sounding build‑up of reflections. Each echo is multiplied by a decaying amplitude (decay_factor^k) and polarity alternates every 3 echoes to create phase‑based movement. ✨ Sparkle is added via a simple high‑pass‑like FIR filter: y = x + sparkle * (x – x[n-1]), boosting the high frequencies of each echo.

Key features v0.2:

Exponential delay progression – creates a dense, evolving tail.
Polarity alternation (every 3 echoes) – adds phase‑based width.
HF sparkle – emphasises transients, adding “air” and shimmer.
Left/right decorrelation – right channel uses slightly different parameters for wide stereo image.
Wet/dry mix control and visualisation of the exponential delay pattern.

Quick start

In Praat, select exactly one Sound object (mono or stereo).
Run script… → Ribbon_Shimmer.praat.
Choose a Preset:
- Subtle Ribbon, Medium Ribbon, Heavy Ribbon, Extreme Ribbon
For custom mode (preset = Custom), adjust parameters as desired.
Set Wet_dry_percent (0 = dry only, 100 = wet only).
Click OK. The script adds a silent tail, generates exponentially‑spaced echoes with HF sparkle, applies wet/dry mix and fadeout, and imports the result as originalname_ribbon_preset.

Tip: Start with Medium Ribbon (95 delays, range 15–1350 ms, decay 0.955) to hear the characteristic ribbon effect. For a more subtle texture, use Subtle (50 delays, range 12–800 ms, decay 0.965). The visualisation shows the exponential spacing.

Important: This effect is implemented entirely in Praat – no Python required. It uses the Formula command to add delayed copies of the signal. For many delays (e.g., 200) on long files, processing can be slow; the script scales the signal every 20 delays to prevent overload.

The 4 presets (+ Custom)

Preset	Delays	Range (ms)	Decay	Sparkle	Description
Subtle Ribbon	50	12–800	0.965	0.20	Light, gentle shimmer.
Medium Ribbon	95	15–1350	0.955	0.25	Balanced, clear ribbon effect.
Heavy Ribbon	140	12–1800	0.945	0.30	Dense, prominent tail.
Extreme Ribbon	200	10–2500	0.935	0.35	Extreme, cavernous shimmer.

The exponential delay law

📐 Delay law

delay[k] = min_delay × (max_delay / min_delay)^(k / number_of_delays)

where k = 1, 2, …, number_of_delays.

min_delay – delay of the first echo.
max_delay – delay of the last echo.
The ratio max_delay / min_delay determines how much the delays spread out.

This produces a dense cluster of early reflections that gradually become sparser – mimicking natural room acoustics where early reflections are dense and late reflections are sparse.

📐 Amplitude law

amp[k] = base_amplitude × decay_factor^k × (±1 polarity)

Polarity flips every 3 echoes (for the left channel) to create phase‑based movement. The right channel flips every 4 echoes for decorrelation.

📐 HF sparkle

Each echo is processed with: y = x + sparkle × (x – x[n-1])

This finite‑difference filter emphasises changes between samples – i.e., high frequencies. At 44.1 kHz, this gives a gentle boost starting around 5 kHz. The sparkle_amount parameter controls the strength.

Parameters & defaults

Ribbon parameters

Parameter	Range	Default	Description
Tail_duration_s	any positive	0.5 s	Length of silent tail added after the original sound (allows echoes to ring out).
Number_of_delays	integer ≥1	95	How many discrete echoes to generate.
Base_amplitude	0–1	0.24	Amplitude of the first echo.
Min_delay_s	any positive	0.015 s (15 ms)	Delay of the first echo.
Max_delay_s	any positive	1.35 s	Delay of the last echo.
Decay_factor	0–1	0.955	Multiplicative decay per echo (applied after base_amplitude).
Sparkle_amount	0–1	0.25	Strength of high‑frequency boost (differentiator).

Mix & output

Parameter	Range	Default	Description
Wet_dry_percent	0–100	60	0 = dry only, 100 = wet only.
Fadeout_duration_s	any positive	1.0 s	Cosine fade‑out applied at the end of the tail to avoid clicks.
Draw_visualization	yes/no	yes	Show waveforms, delay pattern, and summary in Praat picture.
Play_result	yes/no	yes	Auto‑play after processing.

Visualization (Praat picture)

When Draw_visualization = 1, the script draws:

Original waveform (grey).
Result waveform (purple) with wet/dry percentage.
Exponential delay pattern – a scatter plot of echo impulses:
- X‑axis = delay time in milliseconds (exponential spacing visible).
- Y‑axis = amplitude (positive and negative for polarity).
- Positive polarity echoes are blue, negative polarity echoes are red.
- A dotted grey line shows the theoretical decay envelope (base_amplitude × decay_factor^k).
Parameter summary – number of delays, range, decay factor, sparkle amount.

Tip: The delay pattern plot clearly shows the exponential spacing: echoes start dense (left side) and become sparser as delay increases. The alternating polarity (blue/red) adds phase texture.

FAQ / troubleshooting

Processing is very slow

Each delay adds a Formula pass. For 200 delays on a long file, this can be slow. Reduce Number_of_delays for faster preview, or use the Subtle preset (50 delays).

Output is silent / no shimmer heard

Check that Wet_dry_percent is not 0. Also verify that Number_of_delays is ≥10 and Base_amplitude is not too low. The script prints the first few delays in the Info window – if they seem reasonable, the effect should be audible.

Sparkle sounds harsh / causes clipping

The sparkle is a simple differentiator. If it causes clipping, reduce Sparkle_amount (e.g., to 0.1). The script scales the signal after each sparkle pass to prevent runaway amplification.

Right channel differences

To create a wide stereo image, the right channel uses:

Min delay ×1.13, max delay ×0.98
Base amplitude ×0.96, decay factor –0.005
Sparkle amount ×0.8
Polarity alternation every 4 echoes (instead of 3)

This ensures left and right are decorrelated without sounding obviously different.

Understanding the exponential law

With min_delay = 15 ms, max_delay = 1350 ms, and 95 delays, the ratio max/min = 90. The k‑th delay is 15 × 90^(k/95). This means delays increase slowly at first (many early reflections) and faster later (fewer late reflections) – exactly what happens in a real room.