With the V1.0 firmware in the 18F2525 PIC controller (written by Johannes Taelman), we got following correspondence between the controller #7 value and the motor frequency:

Controller 7 value Motor frequency

wind pressure

10 mm H20 = 1 mbar

 remarks
0 0    
10 9.6 Hz   motor standby value
20 18.8 Hz   this is the lowest limit for getting the pipes to speak
30 27 Hz    
40 34 Hz   pitch may be a quartertone down
50 42 Hz 43 mm H2O good for normal playing, but pitch will be a bit low
60 47 Hz 45 mm H2O this is the reference value for normal playing, tuning and intonation. A= 440 Hz
70 49 Hz    
80 49.8 Hz    
90 50.2 Hz    
100 51.8 Hz 50mm H20 this would be the nominal pressure for the given motor.
110 53.5 Hz    
120 53.8 Hz    
127 55.9 Hz 65 mm H20