System Tuning
Tuning a system means getting the PA to respond consistently — in both tone and timing — before anyone tries to mix a show on it. The core technique is a dual-channel FFT transfer function, and the concept is more approachable than the name suggests. You send the same signal to two places at once: into the sound system, and into a measurement microphone out in the room. The analyzer then compares what you put in with what the mic actually hears, and the difference between them is the system's true behaviour.
That comparison gives you three things to read. Magnitude is the tonal balance — where the system is bright or dull. Phase is the timing relationship across frequency, which tells you whether different parts of the system are arriving together. Coherence is a confidence meter, telling you how much to trust the measurement at each frequency, so you do not chase numbers that are really just noise. With that picture in front of you, you EQ to smooth out the gross tonal imbalances toward a sensible house target curve, and then you align arrival times so that sources add together instead of cancelling.
Delay is the key tool for that alignment. You time the subwoofers to the main speakers so the crossover region reinforces rather than fights, and you delay the fills and distributed speakers back to the mains so the whole room hears a coherent attack instead of a smear of slightly different arrivals. All of this happens before the show, on a quiet stage, so that when you finally do mix, you are working on a neutral, predictable system where a fader move means exactly what you intend. Skip the tuning and you spend the entire night fighting the room instead of mixing the band.
Tune the system first — mixing comes second.