Pennsy had exactly two whistles: the single-chime "banshee" freight whistle and the multi-chime passenger whistle. That's it. The multi-chime whistle was applied to later freight classes like the M1 4-8-2's. Other freight power often had their single-chime whistles changed out during the 1940's-50's.
The different pitches were due to the different boiler pressures in the locomotives: 205 psi for K4s and L1s vs. 250 psi for I1s, M1/M1a and 270 psi for M1b.
