octpch — Converts a pitch-class value to octave-point-decimal.

**octpch** (pch) (init- or control-rate args only)

where the argument within the parentheses may be a further expression.

*octpch* and its related opcodes are really *value converters* with a special function of manipulating pitch data.

Data concerning pitch and frequency can exist in any of the following forms:

**Table 18. Pitch and Frequency Values**

Name | Abbreviation |
---|---|

octave point pitch-class (8ve.pc) | pch |

octave point decimal | oct |

cycles per second | cps |

Midi note number (0-127) | midinn |

The first two forms consist of a whole number, representing octave registration, followed by a specially interpreted fractional part. For *pch*, the fraction is read as two decimal digits representing the 12 equal-tempered pitch classes from .00 for C to .11 for B. For *oct*, the fraction is interpreted as a true decimal fractional part of an octave. The two fractional forms are thus related by the factor 100/12. In both forms, the fraction is preceded by a whole number octave index such that 8.00 represents Middle C, 9.00 the C above, etc. Midi note number values range between 0 and 127 (inclusively) with 60 representing Middle C, and are usually whole numbers. Thus A440 can be represented alternatively by 440 (*cps*), 69 (*midinn*), 8.09 (*pch*), or 8.75 (*oct*). Microtonal divisions of the *pch* semitone can be encoded by using more than two decimal places.

The mnemonics of the pitch conversion units are derived from morphemes of the forms involved, the second morpheme describing the source and the first morpheme the object (result). Thus *cpspch*(8.09) will convert the pitch argument 8.09 to its *cps* (or Hertz) equivalent, giving the value of 440. Since the argument is constant over the duration of the note, this conversion will take place at i-time, before any samples for the current note are produced.

By contrast, the conversion *cpsoct*(8.75 + k1) which gives the value of A440 transposed by the octave interval *k1*. The calculation will be repeated every k-period since that is the rate at which *k1* varies.

Note | |
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The conversion from |

Here is an example of the octpch opcode. It uses the file *octpch.csd*.

**Example 694. Example of the octpch opcode.**

See the sections *Real-time Audio* and *Command Line Flags* for more information on using command line flags.

<CsoundSynthesizer> <CsOptions> ; Select audio/midi flags here according to platform ; Audio out Audio in -odac -iadc ;;;RT audio I/O ; For Non-realtime ouput leave only the line below: ; -o octpch.wav -W ;;; for file output any platform </CsOptions> <CsInstruments> ; Initialize the global variables. sr = 44100 kr = 4410 ksmps = 10 nchnls = 1 ; Instrument #1. instr 1 ; Convert a pitch-class value into an ; octave-point-decimal value. ipch = 8.09 ioct = octpch(ipch) print ioct endin </CsInstruments> <CsScore> ; Play Instrument #1 for one second. i 1 0 1 e </CsScore> </CsoundSynthesizer>

Its output should include a line like this:

instr 1: ioct = 8.750