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• Monotonic melodies 1.88 MB

• Dixie and Silent Night 1.3 MB
  • Dixie is monotonic
  • Silent Night is in two-part harmony.

• Neal Hefti’s Batman theme with a few four-part chords 500 KB

• Four part harmony 4 MB
  • A four fold and a seven fold Amen
  • O Maria, diana stella (Oh, Maria, morning star) from Laude Spirituali (1563)
  • Franz Schubert’s Ave Maria

How the Harmony was Achieved

Any one of four single bit positions of a particular register in the Q-7 could be output on an audio speaker located on the Duplex Maintenance Console. This facility enabled on-duty maintenance personnel to sense when the active computer (of the two available) was emitting its normal white noise vs. when it had halted or was sounding irregular. That would alert them that a switchover between the computers might be needed.

By alternating the on/off state of such a bit position at a particular frequency, a musical note could be created by the resultant square wave. For harmony, a chord is desired, e.g., the C major chord:

However, any one bit position can only output one frequency at any one time, so a system was created which played chords as very rapidly repeated arpeggios.

Experiments were conducted to realize the most rapid arpeggios possible, while still preserving the audibility of each note. It was also desired that there should be an apparent equality of volume for each of the four notes in the chord. It was found that the proportion of time needed by each note in the chord differed as a function of frequency.

The original design and experiments were conducted by USAF Captains Price M. Collins and Henry O. Spencer, and the assembler coding and harmonic arrangements were devised by Captain Spencer.

For aficionados: The note A above Middle C is set to a frequency of 440 hertz (cycles per second). The traditional “well-tempered” scale doubles in frequency between octaves, and octaves are divided into twelve half-steps. Therefore, the frequency of a note is obtained by multiplying the frequency of the note which is a half-step below it by