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octpch - convert octave.pitch-class (oct.pc) to linear octaves


Synopsis

linoct = octpch(octpcval)


Description

Given a pitch in "octave.pitch-class" notation (oct.pc), octpch returns that value as a linear octave value. 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.

Linear octaves are similar to octave.pitch-class (oct.pc) notation in that 8.00 is middle C, 9.00 is the C an octave above, etc. The difference is that the fractional part of the specification represents a direct mapping onto the notes of the scale between octaves. For example, in oct.pc notation the value 8.06 represents F-sharp (the tritone, 1/2 the chromatic scale between 8.00 and 9.00). This would be represented as 8.5 in linear octaves.

The fun thing about these notations is that you are not limited to keyboard-notes. An octave.pitch-class 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. The linear octave representation will reflect this absolute frequency value. Different RTcmix instruments will require the pitch or frequency to be specified in different ways.

NOTE: With the exception of boost, The RTcmix conversion functions follow a pattern. The command isdivided into two halves, the one closest to the argument represent the format of the argument, and the one closest to the assignment represents the format to be returned. For example, "cpspch" is divided into "cps" and "pch". The argument is in oct.pc form ("pch") and the return value will be in cps ("cps").

The various format specifiers are:

   amp = absolute amplitude (16-bit, 0-32768)
   cps = cycles per second (Hz)
   db = decibels
   midi = midi note # (60 is middle C)
   oct = linear octaves (8.5 is halfway between octave 8.00 [middle C] and 9.00)
   pch = octave.pitch-class (oct.pc; 8.00 is middle C, 8.02 is D, 8.12 = 9.00 = C above middle C)
   let = note-letter specification ("C4" is middle C, "C#4" is C-sharp above middle C,
      "Gb5" is G-flat the octave above middle C octave. [see pitch-reps for more info])


Arguments

octpcval
Any number, floating point or integer, representing an linear octave pitch value


Examples

   linval = octpch(8.07)
   linval = octpch(7.09425)

See Also

ampdb, boost, dbamp, cpslet, cpsmidi, cpsoct, cpspch, midipch, octcps, octlet, octmidi, pchcps, pchlet, pchmidi, pchoct