Ah, quantitative vs. qualitative measurements.
I did plenty 'audio proofs', or EPM's for AM broadcasters. The hardest part was always getting a true demodulation of a complex carrier wave into a distortion analyzer.
Sometimes a simple swamped diode fed attenuated RF did the job, other times the audio out from the mod monitor was the ticket. All in all, it was a paper chase to please the FCC inspector if he ever set eyes on it in the stations' files.
Just numbers.
For the best tonality, out came a good set of phones and a Streisand LP. Maybe Placido Domingo. Both of them had extremely rich voices, fragile voices that could turn to mush if ANYTHING from the turntable thru the detector was not right.
Fresh stylus. Headroom. Balanced modulator current. Audio bandwidth. RF bandwidth. Good tubes throughout. Is it below audibility with no program?
All could be summarily judged in real time by good ears.
Afterwards, every time, managers and program directors were pleased and always wondered just 'what did you do?
So try pumping some hi-fi audio into that mic jack and see what sounds like on a good radio. You can't ask for more than that...
73DG