pylevelator 1.2.0

Modern Python audio leveling tool — 40% faster than the original Levelator

PyLevelator

中文文档

A modern Python implementation of the Levelator audio leveling tool, with a command-line interface and Python API.

Features

• Fast — ~40% faster than the original C++ Levelator (1.8s vs 3.0s for 30s audio)
• Cross-platform — Windows, macOS, Linux; Python 3.8+
• Easy to install — pip install pylevelator
• Configurable — tune RMS target, gain limits, smoothing, lookahead
• CLI + API — use from the command line or integrate as a library

Performance

Benchmarked on 30s audio (44.1 kHz, mono, Intel i7, 8 threads):

Implementation	Time	Relative
Original Levelator (C++, 2010)	3.0s	1.0×
PyLevelator	1.8s	1.7× faster

How It Works

PyLevelator processes audio through five stages to balance loudness:

1. RMS Envelope Calculation — slides a window (default: 0.5s) over the audio and computes the root-mean-square energy at each position. This gives a smoothed representation of how loud the audio is at every moment.

2. Gain Curve Calculation — at each sample, computes how much gain (in dB) is needed to bring the local RMS up to the target level. Gain is clamped to the [min_gain, max_gain] range (default: [-10 dB, +20 dB]).

3. Gain Smoothing — applies a moving-average filter (default: 0.3s) to the gain curve so that adjacent samples don't jump abruptly. Without this, the output would sound "choppy" or "pumping".

4. Lookahead Limiting — scans forward in time and pre-emptively reduces gain before any peak that would exceed the clipping threshold. The reduction is spread over the preceding lookahead window (default: 0.1s). This is the key step that makes Levelator sound natural — it reacts to peaks before they happen rather than after.

5. Gain Application — multiplies each audio sample by its corresponding gain value and hard-limits the output to ±0.99 to prevent digital clipping.

The result: quiet passages are boosted, loud passages are gently tamed, and the overall recording feels consistently loud without the "pumping" artifacts of simple compressors.

Installation

From PyPI (recommended)

pip install pylevelator

Pre-built wheels for Python 3.8–3.11 on Windows, macOS (arm64 + x86_64), and Linux.

From source

Requires a C compiler with OpenMP support:

• Windows — MSVC (Visual Studio 2019+)
• macOS — libomp (brew install libomp)
• Linux — GCC with libgomp

git clone https://github.com/KakaruHayate/pylevelator.git
cd pylevelator
pip install .

Quick Start

Command line

pylvl -i input.wav -o output.wav
pylvl -i input.wav -o output.wav --target-rms 0.15
pylvl -i input_dir/ -o output_dir/
pylvl --help

Python API

from pylevelator import Levelator, process

# Basic usage
lv = Levelator()
lv.process("input.wav", "output.wav")

# Custom parameters
lv = Levelator(target_rms=0.15, max_gain=18.0, smoothing=0.4)
lv.process("input.wav", "output.wav")

# One-liner
process("input.wav", "output.wav", target_rms=0.15)

CLI Options

Flag	Default	Description
-i, --input	required	Input audio file or directory
-o, --output	required	Output audio file or directory
--target-rms	0.12	Target RMS level (0.0–1.0)
--window-size	0.5	Analysis window in seconds
--smoothing	0.3	Gain smoothing window in seconds
--max-gain	20.0	Maximum gain in dB
--min-gain	−10.0	Minimum gain in dB
--lookahead	0.1	Lookahead time in seconds
--pattern	*.wav	File pattern for batch mode
-v, --verbose	off	Verbose output

Parameter Guide

• target-rms — target loudness level. Higher = louder output.

  • Podcasts / voice: 0.15–0.20 (louder)
  • Music / dynamic content: 0.08–0.12 (preserve dynamics)
  • Default (0.12) is roughly −18 dBFS.

• window-size — how quickly the algorithm reacts to volume changes.

  • Smaller (0.2–0.3s): faster, more aggressive
  • Larger (0.5–1.0s): slower, smoother, preserves dynamics

• smoothing — how smooth the gain transitions are.

  • Larger (0.4–0.6s): fewer abrupt changes, may feel sluggish
  • Smaller (0.1–0.2s): quicker response, may sound less natural

• max-gain / min-gain — safety rails.

  • Lower max-gain if you hear noise in boosted quiet sections.
  • Raise min-gain if you want to preserve the original dynamics more.

• lookahead — time window for the peak limiter.

  • Larger (0.15–0.2s): more clipping protection, slightly slower response
  • Smaller (0.05–0.1s): snappier, less headroom

Supported Formats

PyLevelator uses soundfile for I/O, supporting: WAV, FLAC, OGG, AIFF, CAF, and more. The output format matches the input format automatically.

License

MIT — see LICENSE.