Fixing Claude Code Voice Mode on WSL2

The Problem

If you try /voice in Claude Code on WSL2, you'll likely see a wall of ALSA errors:

ALSA lib confmisc.c:855:(parse_card) cannot find card '0'
ALSA lib conf.c:5207:(_snd_config_evaluate) function snd_func_card_inum returned error: No such file or directory
...
ALSA lib pcm.c:2722:(snd_pcm_open_noupdate) Unknown PCM default

WSL2 doesn't expose physical sound hardware. There are no ALSA sound cards, so any application that tries to open the default ALSA PCM device fails immediately.

What WSLg Provides

WSLg (the GUI/multimedia layer in WSL2) actually runs a PulseAudio server that bridges Windows audio over RDP. You can verify this yourself:

pactl info | grep -E "Server Name|Default Source|Default Sink"

You should see RDPSink (speakers) and RDPSource (microphone). The audio infrastructure exists; the problem is that nothing connects ALSA to it. Applications using PulseAudio natively work fine, but anything going through ALSA (including Claude Code's native audio module) hits a dead end.

The Fix

Two packages solve this. On Arch Linux:

sudo pacman -S pulseaudio-alsa alsa-utils

On Ubuntu/Debian:

sudo apt install pulseaudio-utils alsa-utils

pulseaudio-alsa installs the ALSA PulseAudio plugin and drops config files into /etc/alsa/conf.d/ that redirect all ALSA calls through PulseAudio. alsa-utils provides arecord, which matters because of how Claude Code selects its audio backend.

Why Both Packages Matter

Claude Code tries three recording methods on Linux, in order:

1. A native CPAL/ALSA module (compiled into the binary)
2. arecord (from alsa-utils)
3. rec (from SoX)

The native module talks to ALSA directly through snd_pcm_open. In theory, pulseaudio-alsa should make this work by routing those calls through PulseAudio. In practice, the native module doesn't always behave well through the PulseAudio ALSA plugin. In my case, installing pulseaudio-alsa alone fixed the error messages but voice mode still couldn't capture audio. PulseAudio itself was working (I verified with parecord), but the native CPAL module sitting between Claude Code and ALSA wasn't picking it up.

arecord works reliably through the same plugin. Installing alsa-utils gives Claude Code a working fallback when the native module fails. Without it, Claude Code would need SoX as a last resort, which is a heavier dependency for a single rec command.

Verifying It Works

After installing both packages, you can confirm audio capture is working before trying /voice again:

# Test that arecord captures real audio (not silence)
timeout 3 arecord -f S16_LE -r 16000 -c 1 -t raw -q /tmp/test.raw
python3 -c "
import struct
data = open('/tmp/test.raw', 'rb').read()
samples = struct.unpack(f'<{len(data)//2}h', data)
print(f'Max amplitude: {max(abs(s) for s in samples)} / 32767')
"

If the max amplitude is above zero, your microphone is being captured. Make sure your mic is also enabled in Windows sound settings, since WSLg bridges whatever Windows has active.

No reboot or service restart is needed. Run /voice in Claude Code and it should work immediately.