Two inputs are needed
The transfer function compares two signals: what goes into the system (the reference, on input 1 of a sound card) and what the microphone hears (the measurement, on input 2).
The sound is analysed on your device: nothing is sent.
Nothing kept here. Press “Keep” during a measurement, or import a file.
The two inputs
How to connect?
The reference is the signal that goes into the system (for example an output of the mixing desk, or the generator looped back into the sound card); the measurement is the microphone, in front of the loudspeaker. Any sound will do, music too.
What the measurement gives
Magnitude and phase of H = measurement / reference (the H1 estimator), after delay compensation; the coherence (from 0 to 1) tells you where to trust the curve: below 0.5, noise or reflections dominate and the curve is faded. On the test bench, a synthetic bell filter is recovered to better than 0.2 dB and 2°, and a 5.3 ms delay to within one sample. The measurement microphone is corrected by its calibration file (magnitude only).
Generator
Turn the volume down before starting the generator, then raise it gently (ears and loudspeakers).
The generator plays during the measurement, on this output. Output names appear once the microphone is allowed.
Audio input and measurement microphone
Device names appear after you first allow the microphone.
The file supplied with a measurement microphone (miniDSP UMIK-1, Dayton EMM-6, calibrated Behringer ECM8000…): lines of “frequency gain_dB [phase]”. The correction is applied before the weightings (sound level meter) and to every band (acoustics). Keep the same gain on the sound card as during calibration.