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Expnote.DAT Arb File

This is a 1024-point Arb file created with the Convert Text File to .DAT option in the File menu. It contains 7 separate sections, holding values corresponding to musical intervals and an exponential curve.

This file is intended for use with Arb Freq set to 0 Hz, and the main Phase set to select the desired section of the file. You then use Phase Modulation to cause the output to run through the selected values. The modulator Source can be another Stream, perhaps one of the Noise Waves used in Step Timing mode to randomly select values from the Arb at some desired rate.

The Arb Wave can be set to Round to insure that only discrete table values are selected, as you might want to do if they are used to play musical notes. Or it can be set to Interpolate to allow a smooth curve to be generated for exponential control of a frequency sweep.

The output of the phase-modulated Arb stream would typically be used to modulate another stream, such as via FM to play notes or sweep frequencies using the exponential response provided by the Arb.

The seven sections are:

     Degrees            Description
   0.0 to  38.7     111 semitones (all keys)
  39.0 to  61.5     65 white keys (C-scale)
  61.9 to  77.7     46 black keys (pentatonic)
  78.0 to 100.5     65 natural minor scale
 100.9 to 123.4     65 harmonic minor scale
 123.8 to 143.1     56 whole-tone scale
 143.4 to 360.0     616 freqs, 1/72nd-octaves

(Note that 1/72 octave equals 1/6 semitone.)

The Phase Modulator Depth and the source stream Level must be adjusted to keep the excursion within the desired range. These two controls act in tandem. If you want to select only the last section of this Arb file, for example, it comprises 616/1024 or about 60% of the full 360 degree range. If you set the modulating source Level to 60%, then (assuming that its wave normally covers the full range of values from negative to positive full-scale) this represents the desired extent of the Arb cycle. So you would set the Arb Phase to the middle of the range (about 251.7 degrees) and set the Phase Modulator Depth to 50% to swing +/-50% of the Source amount in each direction.

See also Composer.GEN Setup File


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