fidelis

Bit-perfect Linux music player for external USB DACs. ALSA-direct: decoder → hw: → DAC. No sound server in the audio path, no resampling, no DSP, no software volume.

The DAC is held exclusive while playing. Sample rate switches per track. The Pipeline page in the UI shows the live state of every stage and a three-state bit-perfect verdict.

PCM only in 1.0. DSD and CUE land in 1.1.

Build

Arch:

sudo pacman -S meson ninja pkg-config gcc \
  alsa-lib flac mpg123 libvorbis opus \
  sqlite sdbus-cpp systemd-libs nodejs npm

git clone https://github.com/neofytr/fidelis
cd fidelis
( cd web && npm ci && npm run build )
meson setup build
ninja -C build

Debian and Fedora package lists are in BUILDING.md.

Run

./build/fidelis

UI at http://localhost:7800. First connected USB DAC is selected automatically; switch via the DAC button.

Config lives at ~/.config/fidelis/config.toml:

[device]
preferred = "hw:CARD=SE,DEV=0"   # or a stable fingerprint id (DAC picker writes this)

[audio]
period_ms    = 12
period_count = 4
rt_policy    = "auto"            # auto | fifo | other

[library]
roots = ["/home/user/Music"]

Keys

Volume keys drive the DAC's own mixer (e.g. PCM,0 on an iFi) via ALSA. There is no software volume.

CLI

fidelis ctl status | play | pause | toggle | next | prev | clear
fidelis ctl enqueue /path/to/track.flac

Bind these to media keys in your WM for global control.

systemd

mkdir -p ~/.config/systemd/user
cp packaging/fidelis.service ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now fidelis
loginctl enable-linger "$USER"   # keep running across logout

Realtime audio

sudo gpasswd -a "$USER" audio
sudo install -m 0644 packaging/limits-fidelis.conf \
  /etc/security/limits.d/99-fidelis.conf

Log out and back in. The Pipeline page shows whether SCHED_FIFO was granted.

Exclusive DAC access

fidelis opens the DAC O_EXCL. PipeWire can't share. To stop PipeWire claiming a specific device (replace VID/PID):

# /etc/udev/rules.d/90-fidelis-exclusive.rules
SUBSYSTEM=="sound", ATTRS{idVendor}=="2fc6", ATTRS{idProduct}=="f082", \
    ENV{ACP_IGNORE}="1", ENV{PULSE_IGNORE}="1"

sudo udevadm control --reload && sudo udevadm trigger

Tests

meson test -C build

needs-alsa and needs-loopback suites need real hardware and are skipped otherwise.

License

GPL-3.0-or-later.