Re: Cps2pch

patrick pagano <ppagano@bellsouth.net> asked:

>has anyone been using the Cps2 opcode?
>I would like to get some more info on how to apply it to JI if at all
>possible

Pat,

Normally the cps2pch opcode is used to translate pitches of n tones per
octave equal temperament. The cpsxpch opcode is used to translate pitches
of n tones per arbitrary ratio equal temperament (like Bohlens-Pierce).
However, cps2pch can be used to refer to a frequency multiplier table if
the second parameter is negative. In that case, its absolute value, instead
of being the number of pitches per octave, is the table number. The table
can contain the ratios of just intonation (or anything else of course).
Here is an example. If in your score you have the frequency table (couldn't
resist the harmonic seventh):

;table # start size gen fn C C# D Eb etc.
f 1 0 16 -2 1.000000 1.066667 1.125000 1.200000
1.250000 1.333333 1.440000 1.500000 1.600000 1.666667 1.750000
1.875000

and use it together with the following conversion in your instrument:

ifreq cps2pch p5,-1 ; refer to multiplier table #1

You will have a 12-tone JI scale. Note that the size has to be a power of
two, even if you don't use all the points in the table. Note also that the
gen function number has to be negative to inhibit rescaling. You also have
to be careful not to refer out of the range of the table, for example the
pitch 8.12. cpspch will know that this pitch is equivalent to 9.00, but
cps2pch doesn't know how big your table is and will multiply your pitch by
whatever garbage is in the 13th point of the function table.

I hope this helps.

Bill

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