10. Glossary

The terms this manual (and the audiophile world) takes for granted — two lines each.

AirPlay — Apple's streaming protocol. The box receives AirPlay (via shairport-sync): your iPhone or Mac streams to it like to any AirPlay speaker.

ALSA — the Linux kernel's audio layer. "ALSA device" = a sound card output as the OS sees it; Audiogravi^ty resolves your DAC to one automatically.

Bit-perfect — the audio samples reach the DAC exactly as stored in the file: no resampling, no software volume, no mixing. The guided setup generates bit-perfect configs by default.

Control point — the UPnP role that drives playback on another device. Audiogravi^ty is a control point when it casts to a network renderer.

DAC — Digital-to-Analog Converter, the component that turns the digital stream into the analog signal your amplifier plays. USB, HAT, HDMI or S/PDIF-attached.

DSD — Direct Stream Digital, the 1-bit high-rate format of SACD lineage (DSD64/128/256…). The player shows a DSD lock when a DSD stream plays natively.

Engine — the software that actually renders audio on the box: MPD, shairport-sync (AirPlay), Roon Bridge, HQPlayer NAA. Audiogravi^ty conducts engines; it doesn't replace them.

FLAC — the lossless compressed audio format most hi-res catalogues use. Lossless = decodes to the exact original samples.

Gapless — playback (or an output switch) with no silence inserted between tracks — essential for live albums and continuous mixes.

Hi-Res — better-than-CD resolution: more than 16-bit / 44.1 kHz, typically 24-bit at 96 or 192 kHz. The HI·RES badge in the player flags it live.

MPD — Music Player Daemon, the core playback engine: it plays your local library and carries Qobuz, Tidal, HIGHRESAUDIO and internet radio.

mDNS / Bonjour — the LAN protocol devices use to announce themselves (AirPlay, .local hostnames). Needs multicast to work — see 9. Troubleshooting.

NAA — HQPlayer's Network Audio Adapter: the box receives HQPlayer's processed stream and hands it to the DAC, keeping the heavy DSP on another machine.

Passkey — password-less login credential bound to a device (Face ID, Touch ID, hardware key) via the WebAuthn standard. Requires HTTPS on a real domain.

PCM — Pulse-Code Modulation, the "normal" digital audio representation (CD, FLAC, streaming). Contrast with DSD.

Output — where the sound physically comes out: your local DAC, or a network speaker. Not to be confused with the player that drives it (MPD, AirPlay…) — a DAC does not take a "pause" command. Only one output carries the music at a time.

Processor — a step that transforms the audio between the source and the output, without being either. HQPlayer is the processor in an Audiogravi^ty chain: the music still comes from your library, and still ends at your DAC.

PWA — Progressive Web App: the Audiogravi^ty interface installed from the browser onto your home screen, running fullscreen like a native app.

Renderer — the UPnP role that plays audio. Network amplifiers and streamers are renderers; the box itself is one too (via upmpdcli) so other apps can cast to it. In Audiogravi^ty a renderer is an output: what you cast keeps its own identity (Qobuz, your library…) and the renderer is where it comes out.

Sample rate / bit depth — how often the signal is measured (44.1–384 kHz) and how finely each measurement is stored (16/24/32-bit). Shown live in the hi-fi readout.

S/PDIF · TOSLINK — the coaxial (electrical) and optical variants of the same consumer digital-audio link between box and DAC.

UPnP / DLNA — the LAN protocol family for media discovery and playback: media servers expose libraries (e.g. MinimServer), renderers play, control points conduct.

upmpdcli — the bridge that presents MPD as a UPnP renderer, letting other apps cast to the box.