Airplay and Spotify with Signal Cancel (ThinkPad ALC257)

How I got AirPlay (and Spotify Connect) working on a ThinkPad with ALSA only—and killed the idle hum

PulseAudio/pipewire wasn’t cooperating on my ThinkPad (Realtek ALC257). I wanted Shairport-Sync (AirPlay) and librespot (Spotify Connect) to play directly through ALSA, mix with each other, and not buzz when idle. Here’s the exact setup that finally worked.

Hardware & goal

• Laptop: ThinkPad T-series
• Codec: Realtek ALC257
• ALSA only (no PulseAudio/pipewire)
• Services:
  • Shairport-Sync (AirPlay receiver)
  • librespot (Spotify Connect)
  • Hum silencer keep-alive so inputs don’t float (no buzz when idle)

1) Create a shared output with dmix (system-wide)

ALSA doesn’t mix by default. dmix lets multiple apps share the same device. Put this in /etc/asound.conf:

# Mix multiple playback clients on Analog (hw:0,0)
pcm.dmixed_analog {
  type dmix
  ipc_key 1024
  ipc_key_add_uid false   # allow all users/services to share the same segment
  ipc_perm 0666           # read/write for everyone
  slave {
    pcm "hw:0,0"          # ALC257 Analog; verify with `aplay -l`
    rate 44100            # or 48000 if your card prefers it
    format S16_LE
    channels 2
    period_time 0
    period_size 1024
    buffer_size 8192
  }
}

# Route default through dmix (with automatic format conversion)
pcm.!default {
  type plug
  slave.pcm "dmixed_analog"
}

ctl.!default {
  type hw
  card 0
}

If your card is not hw:0,0, change both the pcm "hw:X,Y" and card lines accordingly (aplay -l shows the indexes).
If you switch to 48 kHz later, update all commands/services to match that rate.

2) Add a hum silencer keep-alive (systemd, ALSA only)

Many receivers hum when the source goes idle (the DAC output “floats”). We keep the device lightly busy with a near-zero signal so the analog stage stays biased.

A robust service is a SoX→aplay pipe (SoX generates, aplay talks to ALSA):

/etc/systemd/system/alsa-keepalive.service

[Unit]
Description=Keep ALSA output active to prevent hum (sox->aplay)
After=sound.target
Wants=sound.target
StartLimitIntervalSec=0

[Service]
ExecStart=/bin/bash -lc '/usr/bin/sox -q -r 44100 -c 2 -b 16 -e signed-integer -n -t raw - synth 0 pinknoise vol 0.0006 | /usr/bin/aplay -q -D default -f S16_LE -c 2 -r 44100'
Restart=always
RestartSec=2
Nice=10

[Install]
WantedBy=multi-user.target

Enable it:

sudo systemctl daemon-reload
sudo systemctl enable --now alsa-keepalive.service

Alternative: if you prefer a sub-bass tone that’s usually inaudible:

... synth 0 sine 40 vol 0.001 | aplay ...

3) Configure Shairport-Sync to use default (dmix), not hw:0,0

Depending on how you installed it, your config is either /etc/shairport-sync.conf or /usr/local/etc/shairport-sync.conf. Mine was /usr/local/etc/shairport-sync.conf.

Minimal working config:

general = {
  name = "Tulip Speaker";
  mdns_backend = "avahi";
  log_verbosity = 2;
  output_backend = "alsa";
};

alsa = {
  output_device = "default";       # use dmix, not hw
  use_mmap = "no";                 # safer on some Intel HDA
  output_format = "S16";
  output_rate = 44100;             # match /etc/asound.conf
  mixer_control_name = "Headphone";# pick a control that exists on your card
  mixer_device = "hw:0";
};

Restart and verify logs reference default (not plughw:0,0):

sudo systemctl restart shairport-sync
sudo journalctl -u shairport-sync -b | grep -E 'output device name|PCM handle name'

4) Configure librespot (Spotify Connect) for ALSA + hardware mixer

/etc/systemd/system/librespot.service

[Unit]
Description=Spotify Connect (librespot)
After=network-online.target sound.target
Wants=network-online.target

[Service]
User=spotify
Group=audio
WorkingDirectory=/var/lib/librespot

ExecStart=/usr/local/bin/librespot   -n "Jaybird's Jam"   -B alsa   -d default   -m alsa   -S hw:0   -T "Headphone"   -b 160   -G   -C /var/lib/librespot   -z 8765   -i 192.168.1.115   -v

Restart=always
RestartSec=5
NoNewPrivileges=true

[Install]
WantedBy=multi-user.target

5) Verify

• aplay -D default -f S16_LE -r 44100 /usr/share/sounds/alsa/Front_Center.wav plays.
• systemctl status alsa-keepalive → running (no hum when idle).
• AirPlay + Spotify play together without “device busy”.
• Mixer control (Headphone) adjusts volume correctly.

Final note

This configuration keeps the setup pure ALSA—no PulseAudio, no PipeWire.
Everything shares the same default dmix sink, stays silent when idle, and your ThinkPad’s analog output finally behaves like proper audio gear.