Unified Vibrato Generator — User Guide

Advanced pitch modulation: combines four distinct vibrato and chorus algorithms in a single unified interface for creating expressive pitch variations, from classic vibrato to complex multi-voice chorus effects.

Author: Shai Cohen Affiliation: Department of Music, Bar-Ilan University, Israel Version: 1.0 (2025) License: MIT License Repo: https://github.com/ShaiCohen-ops/Praat-plugin_AudioTools

Contents:

What this does Quick start Vibrato Theory Four Modes Parameters Guide Applications

What this does

This script implements a unified vibrato generator — a comprehensive pitch modulation system that provides four distinct algorithms for creating expressive pitch variations. Unlike simple pitch shifting, this system uses delay-based modulation to create natural-sounding vibrato and chorus effects that mimic performance techniques and analog hardware. The four modes include: (1) Standard Vibrato: Classic constant-speed pitch oscillation. (2) Chirped Vibrato: Accelerating or decelerating pitch modulation for dynamic expression. (3) Rate Modulation: "Wobbly" vibrato with modulated speed for organic, imperfect character. (4) Swarm/Chorus: Multi-voice layered effects that create rich, ensemble-like textures.

Key Features:

Four Modulation Algorithms — From classic vibrato to complex chorus
Delay-Based Processing — Natural pitch modulation without artifacts
Mathematical Precision — Accurate phase accumulation and modulation
Multi-Voice Layering — Rich chorus effects with configurable voices
Dynamic Modulation — Time-varying rates and depths for expression
Efficient Implementation — Real-time capable processing algorithms

What is vibrato vs chorus? Vibrato and chorus are related but distinct modulation effects: (1) Vibrato: Periodic pitch variation applied to a single voice, typically used for expressive emphasis in vocals and instruments. Creates a "wobbling" pitch effect. (2) Chorus: Multiple slightly detuned copies of a signal mixed together, creating the illusion of multiple performers or instruments. Creates "thickening" and "widening" effects. This unified system bridges both concepts: Standard and Chirped modes create true vibrato, while Swarm mode creates chorus-like effects through multi-voice layering. Rate Modulation sits between them, creating complex, evolving pitch variations that have characteristics of both effects.

Technical Implementation: (1) Delay-line modulation: All modes use variable delay lines to create pitch shifts — shorter delays raise pitch, longer delays lower pitch. (2) Mathematical modulation: Sine waves and more complex functions control delay time variations. (3) Phase accumulation: Careful phase tracking ensures smooth pitch transitions. (4) Boundary handling: Robust sample indexing prevents out-of-bounds errors. (5) Multi-voice synthesis: Swarm mode combines multiple modulated copies with phase offsets. The system uses Praat's efficient formula processing and sample-level precision to create professional-quality modulation effects.

Quick start

In Praat, select exactly one Sound object.
Run script… → Unified_Vibrato_Generator.praat.
Choose Mode from four options based on desired effect.
Set Base_delay_ms (3-10ms for typical vibrato).
Adjust Modulation_depth (0.05-0.20 for subtle to strong effects).
Set Base_rate_hz (4-7 Hz for typical vibrato rates).
Configure mode-specific parameters as needed.
Set output normalization and playback options.
Click OK — processing completes quickly.
Output appears with descriptive name based on selected mode.

Quick tip: Start with Standard mode for classic vibrato effects on vocals and solo instruments. Use Chirped mode for expressive effects that accelerate or decelerate. Try Rate Modulation for organic, "wobbly" vibrato that sounds more human and less mechanical. Use Swarm mode for rich chorus effects on synthesizers, guitars, and pads. Base_delay_ms around 5ms works well for most material — shorter delays create sharper pitch changes, longer delays create more subtle modulation. Modulation_depth 0.10 gives noticeable but musical vibrato. Rates around 5-6 Hz match typical vocal and instrumental vibrato speeds. Experiment with different modes to discover their unique characters.

Important: DELAY-BASED PROCESSING — all modes work by varying delay times, which can cause slight time smearing on transients. Extreme settings may cause audible artifacts or pitch inaccuracies. Very high modulation depths can create unnatural pitch variations. Very low base rates (<2 Hz) may not be perceived as vibrato. Swarm mode with many layers can significantly increase processing time. Boundary conditions are handled gracefully, but very short sounds may not show full modulation cycles. Stereo files are processed with identical modulation on both channels. Output normalization preserves the effect character while preventing clipping. Always audition results on representative material.

Vibrato Theory

Delay-Line Modulation Fundamentals

Pitch Shifting Through Variable Delay

Time-stretching principles:

Basic delay modulation: output[n] = input[n + d(n)] Where d(n) is the time-varying delay: d(n) = base_delay × (1 + depth × modulator(n)) Pitch relationship: When delay decreases: playing faster → pitch rises When delay increases: playing slower → pitch falls Constant delay: no pitch change Oscillating delay: vibrato effect Mathematical implementation: sample_index = current_sample + round(base_delay_samples × (1 + modulation_depth × modulator(time))) Key insight: Vibrato = periodic variation of playback speed Implemented through time-varying delay line Creates natural pitch modulation without resynthesis

Why Delay-Based Modulation?

Advantages over pitch shifting:

Natural sound: Mimics how performers create vibrato
Preserves timbre: No spectral processing artifacts
Continuous variation: Smooth pitch transitions
Computational efficiency: Simple sample manipulation
Musical results: Sounds like performance expression

Modulation Mathematics

Phase Accumulation and Waveforms

Sine wave modulation basics:

Standard vibrato modulator: modulator(t) = sin(2π × rate × t) Phase accumulation: phase(t) = 2π × rate × t This creates a linearly increasing phase Delay calculation: delay_samples(t) = base_delay × (1 + depth × sin(phase(t))) Sample reading: read_position = current_sample + round(delay_samples(t)) Why sine waves? Smooth, musical modulation Natural sounding pitch variation No sharp transitions Mathematically pure

Why Complex Modulation?

Beyond simple sine waves:

Expression: Real vibrato varies in speed and depth
Naturalness: Perfect sine waves sound artificial
Musical interest: Complex modulation creates richer effects
Creative possibilities: Unique modulation characters

🎵 Vibrato Intuition

For vocal vibrato:

Rate: 5-7 Hz (natural vocal oscillation speed)

Depth: 10-30 cents (subtle pitch variation)

Result: Expressive, living vocal quality

For string instruments:

Rate: 4-6 Hz (slightly slower than vocals)

Depth: 20-50 cents (more pronounced variation)

Result: Rich, emotional string expression

Multi-Voice Chorus Principles

Ensemble Effect Creation

Layered modulation theory:

Chorus effect principle: Multiple slightly detuned copies create ensemble illusion Each voice has unique modulation characteristics Combined result sounds like multiple performers Swarm mode implementation: FOR each layer i from 1 to N: rate_i = base_rate + (i-1) × layer_spread phase_i = i × (2π / N) [phase offset] depth_i = modulation_depth [same for all layers] voice_i = original[delay_samples(rate_i, phase_i, depth_i)] output = Σ voice_i / N Why this works: Slight rate differences prevent phase cancellation Phase offsets ensure voices don't start in sync Averaging maintains consistent loudness Creates rich, wide stereo-like effect

Why Multi-Voice Effects?

Sonic benefits:

Thickening: Makes single sounds appear ensemble-sized
Spatial widening: Creates stereo-like effect from mono
Complexity: Richer, more interesting textures
Analog emulation: Recreates vintage chorus hardware

Four Modes

🎚️ Comprehensive Modulation System

Complete comparison of all four vibrato and chorus algorithms:

Mode 1: Standard Vibrato

Aspect	Character	Best For	Technical Approach
Modulation	Constant speed, regular	Classic vibrato, vocals	Simple sine wave LFO
Rate Behavior	Fixed frequency	Predictable, musical	base_rate_hz constant
Sound Quality	Clean, pure	Natural instruments	sin(2π × rate × t)
Complexity	Low	Traditional applications	Single modulation source

Mode 2: Chirped Vibrato

Aspect	Character	Best For	Technical Approach
Modulation	Accelerating/decelerating	Expressive solos, effects	Linear frequency sweep
Rate Behavior	Time-varying	Dynamic expression	rate(t) = base + sweep × t
Sound Quality	Evolving, dramatic	Lead lines, synths	Phase integral of rate(t)
Complexity	Medium	Creative applications	Quadratic phase accumulation

Mode 3: Rate Modulation

Aspect	Character	Best For	Technical Approach
Modulation	Wobbly, irregular	Organic sounds, vintage	Modulated LFO rate
Rate Behavior	Modulated speed	Human-like variation	rate(t) = base + sens × sin(2π × mod_rate × t)
Sound Quality	Imperfect, alive	Analog emulation	Nested sine modulation
Complexity	High	Character effects	Complex phase relationship

Mode 4: Swarm/Chorus

Aspect	Character	Best For	Technical Approach
Modulation	Multi-voice, rich	Ensemble effects, pads	Layered detuned voices
Rate Behavior	Distributed rates	Thickening, widening	Multiple LFOs with spreads
Sound Quality	Dense, wide	Synthesizers, guitars	Weighted voice summation
Complexity	Very high	Production effects	Multi-layer processing

Mode Selection Guide

Choosing the right mode:

Use Standard mode when:
- You want classic, predictable vibrato
- Processing vocals or acoustic instruments
- Creating natural performance expression
- You need clean, musical pitch modulation
Use Chirped mode when:
- You want expressive, dynamic vibrato
- Processing lead instruments or solos
- Creating dramatic build-up or release effects
- You need time-varying modulation intensity
Use Rate Modulation when:
- You want organic, human-like vibrato
- Emulating vintage analog effects
- Creating "wobbly" or imperfect modulation
- You need complex, evolving pitch variations
Use Swarm mode when:
- You want rich chorus or ensemble effects
- Thickening synthesizers or electric guitars
- Creating wide, spacious sounds from mono sources
- You need professional production effects

Each mode offers unique creative possibilities for different musical contexts

Creative Mode Applications

🎤 Vocal Expression

Mode: Standard or Chirped

Application: Add natural vibrato to sustained vocal notes

Result: Expressive, living vocal quality that enhances emotion

🎸 Analog Synth

Mode: Rate Modulation

Application: Process analog-style synthesizer patches

Result: Vintage, organic modulation with character and warmth

🎹 Rich Pads

Mode: Swarm/Chorus

Application: Thicken and widen synth pads and strings

Result: Dense, ensemble-like textures with movement and depth

Parameters Guide

⚙️ Complete Parameter Reference

Detailed explanation of all vibrato and chorus parameters:

Common Parameters (All Modes)

Parameter	Range	Default	Description
Base_delay_ms	1.0-20.0	5.0	Center delay time in milliseconds
Modulation_depth	0.01-0.50	0.10	Pitch modulation intensity (0-50%)
Base_rate_hz	0.5-15.0	5.0	Base modulation frequency in Hz
Scale_peak	0.1-1.0	0.99	Output peak normalization level
Play_after_processing	0/1	1	Auto-play result after processing

Chirped Mode Parameters (Mode 2)

Parameter	Range	Default	Description
Sweep_rate_hz_per_sec	-10.0 to 10.0	2.0	Rate change speed (Hz per second)

Rate Modulation Parameters (Mode 3)

Parameter	Range	Default	Description
Rate_sensitivity	0.1-10.0	3.0	Rate modulation depth
Rate_mod_freq_hz	0.1-5.0	0.8	Rate modulation frequency

Swarm Mode Parameters (Mode 4)

Parameter	Range	Default	Description
Number_of_layers	2-12	6	Number of chorus voices
Layer_spread_hz	0.1-2.0	0.5	Rate spread between voices

Parameter Interactions

Key relationships:

Base_delay vs pitch range: Longer delays = wider pitch variation
Modulation_depth vs intensity: Higher depth = stronger vibrato
Base_rate vs speed: Higher rates = faster oscillation
Sweep_rate vs acceleration: Positive = speed up, negative = slow down
Layer parameters vs richness: More layers + wider spread = thicker chorus

Parameters interact differently in each mode to create unique modulation characters

Recommended Settings

🎻 Natural Vocal Vibrato

Mode: Standard

Settings:

Base_delay_ms: 5.0
Modulation_depth: 0.08
Base_rate_hz: 6.0

🎹 Analog Chorus

Mode: Swarm

Settings:

Base_delay_ms: 7.0
Modulation_depth: 0.12
Base_rate_hz: 4.5
Number_of_layers: 4
Layer_spread_hz: 0.3

🎸 Expressive Lead

Mode: Chirped

Settings:

Base_delay_ms: 6.0
Modulation_depth: 0.15
Base_rate_hz: 5.0
Sweep_rate_hz_per_sec: 3.0

Applications

Vocal Production

Use case: Add expressive vibrato to sustained vocal notes

Technique: Use Standard mode with natural rates and depths

Example: Enhance emotional impact in ballad and opera vocals

Instrument Enhancement

Use case: Create vibrato on instruments without natural modulation

Technique: Use Rate Modulation for organic character

Example: Add expression to sampled instruments and synthesizers

Sound Design

Use case: Create rich chorus and ensemble effects

Technique: Use Swarm mode with multiple layers

Example: Transform mono synthesizers into wide, lush textures

Vintage Emulation

Use case: Recreate classic analog modulation effects

Technique: Use Rate Modulation with medium sensitivity

Example: Emulate tape wow and flutter, analog chorus units

💡 Creative Techniques

Advanced applications:

Layered modulation: Process different frequency bands with different modes
Automated parameters: Change rates and depths over time for evolving effects
Extreme settings: Use very high rates or depths for special effects
Combination effects: Process already-modulated sounds for complex results

Troubleshooting Common Issues

Problem: Artifacts or glitches
Cause: Extreme modulation settings or very short sounds
Solution: Use more moderate parameters or longer audio segments

Problem: Effect too subtle
Cause: Low modulation depth or inappropriate rate
Solution: Increase depth or adjust rate for better perception

Problem: Unnatural sounding
Cause: Too regular modulation or extreme settings
Solution: Use Rate Modulation mode or more natural parameters

Problem: Processing too slow
Cause: Swarm mode with many layers on long files
Solution: Reduce layer count or process shorter segments