He's looking for something to give him an automated readout of multiple peak frequencies.
The Smaart Spectrograph gives a visual readout of the peak frequencies as well as the spectral decay.
The exact frequencies can be picked out with the cross hair, but the "character" of the harmonics is easy to see visually.
I just sang, whistled and played some notes on an Ovation acoustic guitar (with ancient strings) using the built in computer mic.
The whistle has very little upper or sub harmonics.
The voice ( "ahhh" notes) has more harmonics (and not as defined pitch, I was sloppy) which are primarily 2nd, 3thd and 4th order, the fundamental note being the strongest.
The guitar fundamentals are not as loud as the harmonics, and the subharmonic on the high E is louder than the fundamental. The upper harmonics on a sustained note initially are similar in harmonic content, but the way they die out is different.
The difference in harmonic arrangement as well as their sustain are the signature of every instrument.
A readout of only the peak frequencies would not give as much of a clue to the harmonic character as a spectrograph, as it would only give a reference at one point in time.