0.7.3 records silence with multichannel Scarlett input; 0.6.10 works

[uuuser-name]

Summary

Hex 0.7.3 records silence with a multichannel USB input interface (Scarlett 2i2 4th Gen), even though the UI enters recording mode normally. The red pill appears, but the input meter does not react and the resulting audio file is silent.

This looks related to the 0.7.2+ capture-engine changes, but it is a different failure mode than the earlier double-tap-lock race: it affects normal shortcut-triggered recording on this interface, not just double-tap lock.

Repro

1. Use Hex 0.7.3 on macOS 26.3
2. Select Scarlett 2i2 4th Gen as the input device in Hex
3. Leave Super Fast mode disabled
4. Start recording with the normal hotkey / modifier-only shortcut
5. Speak into the interface
6. Stop recording

Actual

• The recording UI starts
• The level indicator does not react
• Transcription is empty or effectively empty
• The capture files produced by Hex are silent

Observed locally on 0.7.3:

• Hex logs show the capture-engine path being used (Capture engine armed, Capture engine first buffer)
• The generated hex-capture-*.wav files are flat silence (mean_volume: -91.0 dB, max_volume: -91.0 dB)

Expected

Hex should capture real microphone audio from the selected Scarlett input, the same way older builds did.

Why this looks like a Hex bug

The interface and mic path are fine outside Hex:

• Ableton records from the same Scarlett input normally
• A direct ffmpeg capture from the Scarlett input produces non-silent audio
• A plain AVAudioRecorder test on the same machine and device also produces non-silent audio

The regression split is also very clear:

• 0.7.3: broken, shortcut recording goes through capture engine and produces silent WAVs on this device
• 0.6.10: works immediately on the same machine, same Scarlett input, same hotkey/settings

After downgrading to 0.6.10, the next Hex recording produced a normal non-silent file (mean_volume: -46.9 dB, max_volume: -29.6 dB).

Notes

• The Scarlett enumerates as a multichannel input device on this machine
• From local source inspection, newer Hex builds appear intended to prefer recorder fallback for multichannel inputs, but the 0.7.3 release build here still took the capture-engine path
• This may be a multichannel-device-specific regression in the 0.7.x recording pipeline
• Related older regression reports: double tap lock records no audio #193 and Double Tap does not record on 0.7.2 #195

Environment

• Hex: 0.7.3 when broken, 0.6.10 when working after downgrade
• macOS: 26.3
• Input device: Scarlett 2i2 4th Gen