The RTA display showed a near-perfect frequency response. Pink noise in, pink noise out — flat within ±1 dB from 63 Hz to 16 kHz. The system engineer was confused. 'That can't be right,' he said. 'This room is a concrete box. Nothing sounds flat in a concrete box.'

He was correct to be suspicious. The PA was not producing a flat response. The PA was, in fact, muted. It had been muted since the previous event's teardown. Nobody had unmuted it for soundcheck because the soundcheck hadn't started yet. The engineer was running pink noise from his measurement rig into a muted console channel. No sound was coming from the speakers.

What the RTA was showing was the spectrum of the noise floor: HVAC, traffic rumble, the hum of fluorescent lights, and the steady-state broadband noise of a large empty room. This noise happened to have a roughly pink spectrum — because environmental noise often does — and the RTA, having no way to distinguish between PA output and ambient noise, displayed it faithfully.

The 'perfect' response was the room's ambient noise signature. The engineer had achieved the rare accomplishment of measuring a sound system by not measuring the sound system. When the console was unmuted and the PA actually produced output, the response was, as predicted, terrible. It was a concrete box.

The Moral: Verify your signal chain is active before interpreting results. SonaVyx's transfer function mode uses a known reference signal and coherence to confirm that the measurement reflects the system under test, not whatever else is making noise in the room.