foxLyrionDSP

foxLyrionDSP

Go-based DSP engine for Lyrion Music Server

This is the core signal processing engine that powers the SqueezeDSP plugin. It runs as a standalone binary in the Lyrion/Squeezebox transcoding chain, receiving a raw audio stream via stdin and writing the processed stream to stdout.

End users — you do not need this repository. Install the plugin directly via the Lyrion third-party plugins list. See the SqueezeDSP repository for installation instructions.

Overview

foxLyrionDSP is invoked by Lyrion's transcoding system as part of a pipeline, for example:

flac -dcs -- $FILE$ | foxLyrionDSP --id="xx:xx:xx:xx:xx:xx" --wav=true --wovo=true --d=24 | flac -cs -0 --totally-silent -

It reads settings for the given player ID from the SqueezeDSP configuration, applies the configured DSP chain, and passes the processed audio downstream.

Features

• Parametric Equaliser — Peak, High Pass, Low Pass, High Shelf, Low Shelf filters with configurable frequency, gain, and Q
• FIR Convolution — room correction and impulse response convolution via WAV files, with automatic resampling via SoX to match the incoming sample rate
• Preamp — gain reduction to prevent clipping, particularly important when using convolution
• Balance — left/right channel level adjustment
• Width — stereo width control
• Delay — single-channel delay in milliseconds
• Loudness — bass and treble compensation at lower listening levels
• Per-player configuration — each Lyrion player can have independent settings
• Preset support — save and load named configurations
• Clipping detection — peak level monitoring with log output

Supported Audio Formats

Input is processed from the Lyrion transcoding chain. Output is 24-bit FLAC or 16-bit WAV depending on player capability.

Audio formats with custom transcoding profiles: aac, aif, alc, alcx, ape, flc, mov, mp3, mp4, mp4x, mpc, ogg, ogf, ops, spt, wav, wma, wmal, wmap, wvp

DSD and MQA are not supported.

Architecture

Package Structure

Convolver

The convolver uses a partitioned FFT approach with a ring buffer to process the audio stream efficiently. Key design decisions:

• A custom minimal FFT library (based on ArgusDusty FFT) with cached twiddle factors, optimised for block sizes below 16,386 samples — substantially faster than scientificgo in this range
• Partitioned processing minimises the data discarded after FFT/InverseFFT cycles
• Impulse files are resampled on first use (via SoX) and cached for subsequent tracks at the same sample rate
• Filter building at track start uses an IIR calculation to combine filters rather than a full convolution, giving approximately 10x faster cold starts
• Output gain is managed by calculating the inverse of the final impulse's MaxGain and applying it during the gain stage, rather than normalising the impulse itself

Performance (approximate, streaming with a large room correction impulse):

Building

Requires Go 1.21 or later.

Build all targets (Windows):

Build-All.bat

Build test harness (Windows):

Build-Test.bat

Manual cross-compilation:

# Linux (ARM - Pi)
GOOS=linux GOARCH=arm GOARM=7 go build -o foxLyrionDSP_arm ./foxLyrionDSP.go

# Linux (ARM64)
GOOS=linux GOARCH=arm64 go build -o foxLyrionDSP_arm64 ./foxLyrionDSP.go

# Linux (x86_64)
GOOS=linux GOARCH=amd64 go build -o foxLyrionDSP ./foxLyrionDSP.go

# Windows
GOOS=windows GOARCH=amd64 go build -o foxLyrionDSP.exe ./foxLyrionDSP.go

Testing

A test harness is included for offline development and benchmarking:

go run dsp_tester.go

This allows processing of a local audio file through the DSP chain without requiring a running Lyrion instance.

Command Line Arguments

Platform Support

Tested on: Windows 10/11, Raspberry Pi 3B/4 (Raspbian), Docker (Linux), Ubuntu (VirtualBox), macOS (VirtualBox), PiCorePlayer.

Related

• SqueezeDSP Plugin — the Perl/JavaScript plugin that configures and deploys this engine within Lyrion Music Server
• SqueezeDSP Wiki — end-user documentation
• Lyrion Music Server

License

MIT License — Copyright (c) 2024 Jonathan Fox