pchcps - convert frequency to octave.pitch-class
Given a frequency in Hz (cycles per second), pchcps returns that value expressed in ``octave.pitch-class'' (oct.pc) notation. oct.pc is a way to use standard "western" keyboard notes without having to look up the pitch-frequency conversion. It works by arbitrarily assigning the octave of middle-C to 8.00. Any semitone above middle-C is added as a "hundredth" to the left of the decimal point, i.e. 8.01 is the C# just above middle-C, 8.02 is the D, 8.03 is the D# (Eb), etc. up to 8.12, which is equivalent to 9.00. 9.01 is then the C# one octave and a semitone abouve midddle-C.
The fun thing about this notation is that you are not limited to keyboard-notes. A pitch specification of 7.07542389 will select a frequency that is somewhere about half-way between the G (7.07) and Ab (7.08) just below middle-C. Different RTcmix instruments will require the pitch or frequency to be specified in different ways, although the scorefile commands cpspch, octcps or other related commands can do most necessary conversions.