The buzz appeared during dress rehearsal and vanished during tech checks. It was at 150 Hz — a constant, annoying tone that sat underneath everything like an unwanted organ pedal note. The audio crew checked every cable, every DI box, every ground connection. All clean. The buzz persisted.

They replaced the stage snake. Still buzzing. They ran a direct line from the console to the amplifiers, bypassing everything. Still buzzing. They replaced the amplifier. The buzz continued. At this point, the head of audio was questioning whether 150 Hz was a frequency he had simply never noticed before, like a color that had always been there but he'd only just learned to see.

The key observation was the timing: buzz during dress rehearsal, silence during tech check. What changed between those two events? The lighting. During tech check, the lights were at full. During dress rehearsal, the lights were dimmed for the moody opening scene.

The dimmers were thyristor (SCR) type, chopping the 50 Hz mains waveform. A chopped sine wave generates harmonics. The third harmonic of 50 Hz is 150 Hz. The lighting circuit shared a distribution panel with the audio power supply, and the dimmer harmonics were coupling electromagnetically into the audio mains transformer.

The solution was a power conditioner on the audio supply, isolating it from the dimmer-contaminated mains. The 150 Hz vanished. The lighting designer didn't understand the problem but took credit for solving it.

The Moral: A buzz at a harmonic of mains frequency (50/60 Hz) usually indicates electromagnetic interference, not an audio fault. SonaVyx's hum detector automatically identifies 50/60 Hz harmonics and distinguishes ground loop hum from magnetic interference — pointing you to the electrical panel instead of the cable trunk.