CamillaDSP is a real-time audio stream processing engine written in Rust. It captures audio from a configurable backend (ALSA, PulseAudio, PipeWire, CoreAudio, WASAPI, ASIO, or file), processes it through a user-defined pipeline of filters, mixers, compressors, and other DSP components, and outputs it to a playback device. The pipeline is defined via YAML configuration, supporting biquad filters, FIR convolution (with hand-optimized NEON and AVX+FMA SIMD kernels), loudness, limiting, noise gates, and dithering. A websocket-based control interface allows runtime adjustments of volume, mute, faders, and config reloads. The architecture is modular with separate threads for capture, processing, and playback, using a PI rate controller for buffer level regulation. Benchmarks demonstrate attention to performance. While primarily an application, the DSP filter implementations and utility components (ring buffer, conversion routines, rate controller) are reusable building blocks for audio software.
LosslessSwitcher is a macOS menu bar application that automatically adjusts the audio output device's sample rate and bit depth to match the lossless track currently playing in Apple Music. It works by reading system logs (OSLog) from Music.app and CoreAudio subsystems to detect the current track's sample rate, then uses CoreAudio APIs via the SimplyCoreAudio library to switch the output device's format. The app is not sandboxed because it requires access to system logs and the ability to modify audio device properties. It is built with SwiftUI and uses Combine for event-driven updates. The architecture includes a SwiftUI app entry point (QualityApp.swift), a legacy NSApplicationDelegate for menu bar management and permissions checking, an Observable class (MenuBarController) that owns the OutputDevices and MediaRemoteController, and parser utilities for extracting sample rate and bit depth from console entries. A user can also configure a custom script to run when the sample rate changes. The code demonstrates modern Swift patterns but is tightly coupled to macOS-specific frameworks and the Apple Music ecosystem.
qaac is a command-line audio encoder that uses Apple's CoreAudioToolbox (or the reference ALAC encoder) to encode audio to AAC or ALAC formats. It supports a wide range of input formats (WAV, FLAC, WavPack, Opus, Ogg Vorbis, CAF, and more) via runtime-loaded codec libraries, and outputs to MP4/M4A, ADTS, CAF, WAV, or raw PCM. The architecture follows a clean pipeline pattern: input sources implement the ISource interface, pass through optional DSP filters (resampler, normalizer, limiter, compressor, matrix mixer, etc.), and are written to output sinks. Metadata handling is integrated via vendored taglib, and the encoder supports gapless encoding, chapter markers, artwork, and various tagging formats. The codebase is predominantly C++ with platform-specific adaptations for Windows and macOS, and includes several reusable utility components such as a streaming FFT convolver, ring buffer, and cross-platform dynamic library loader.
musikcube is a cross-platform, terminal-based music player and streaming server written in C++. It consists of a core library (`musikcore`) with a plugin-based architecture for decoders, encoders, audio outputs, DSP, and data streams. The project includes three distinct front-ends: a terminal UI (`musikcube`) built on a custom curses++ framework, a native Windows UI (`musikwin`) using a custom Win32 wrapper, and an Android remote client (`musikdroid`) written in Kotlin. The server plugin enables remote control and audio streaming via WebSocket and HTTP. The core manages a SQLite-backed music library with indexing, metadata extraction (via TagLib), and playlist management. Audio playback supports gapless and crossfade transitions, visualizers, and an equalizer. The system is designed for extensibility through a well-defined SDK interface set, allowing third-party plugins for decoders, outputs, and DSP. The codebase is mature (copyright 2004-2023) and shows signs of organic growth, with heavy vendored third-party dependencies and platform-specific code. While not architecturally pristine, it demonstrates solid engineering, a clean plugin API, and reusable UI frameworks.