PulseAudio

PulseAudio is a network-capable sound server program commonly used on Linux, FreeBSD, and other Unix-like operating systems. Originally developed by Lennart Poettering (also known for systemd) in 2004, PulseAudio served as the default audio server for most Linux desktop distributions for over 15 years before gradually being replaced by PipeWire. PulseAudio provides a daemon (pulseaudio) that sits between applications and the ALSA (Advanced Linux Sound Architecture) kernel-level sound drivers, offering advanced audio routing, mixing, and processing features that ALSA alone cannot provide. Key features include: per-application volume control (independent volume levels for each audio-producing application via pavucontrol), network audio streaming (streaming audio over the network to or from remote PulseAudio servers), Bluetooth audio support (A2DP for high-quality audio, HSP/HFP for headset communication), low-latency audio processing with dynamic resampling (converting between different sample rates using libsamplerate), sample cache (storing frequently used sounds in memory for instant playback), device hot-plugging support (automatically detecting and configuring newly connected audio devices), per-stream routing (directing specific application audio to specific output devices), audio effects via LADSPA and module-system (applying equalizers, compressors, and other DSP effects), surround sound support (up to 7.1 channels), echo cancellation (for VoIP applications), and a TCP-based protocol allowing remote clients to connect.