Hunting a USB audio dropout

My desk speakers hang off a receiver that takes USB audio. Every so often the music would chop: a tiny gap, then back. Sometimes three a minute apart, then nothing for an hour.

Clearing the laptop

The first job was to prove whether the gap started on my side. I checked every layer I could reach:

• The audio itself. I recorded what the sound server actually sent to the device and compared it with the source file. Bit-identical, with the gain at exactly 1.0, no silence and no drift.
• The driver. I sampled the ALSA buffer pointer every 2 ms. It never stalled.
• The sound server. Zero underruns.
• The dock. I moved the cable to a port on the laptop itself. The chops kept coming, so the dock was cleared.
• USB. A packet capture showed zero errors. To be fair, that capture ran after the last chop of the day, so it didn't catch one.

Everything leaving the laptop was clean, even through the chops. So the gap had to be made inside the receiver.

The suspect

Other owners of the same receiver report the same intermittent USB dropouts, and nobody has a fix from the maker. There's no firmware update for it either.

So the test is to take USB out of the chain. Since September 30 the music goes out of the laptop's headphone jack into the receiver's analog input over a plain 3.5 mm to RCA cable. If the chops stay gone, that convicts the USB input. If they come back, I have the capture scripts ready to catch one in the act.