Oscillator CHOP

Summary

The Oscillator CHOP generates sounds in two ways. It synthesizes tones using a choice of common waveforms, or it repeats a prepared incoming audio clip of any duration. The LFO CHOP by default generates waves at lower frequencies and sample rates, though both Oscillator and LFO are interchangeable.

When it is synthesizing tones from the basic waveforms, the Oscillator CHOP steps through the waveform at a rate that depends on the Pitch Control input. By default, a Pitch Control of 0 gives a middle A at 440 Hz; a 1 gives 880 Hz; a -1 gives 220 Hz. Steps of 1 in Pitch Control are 1 octave apart. Steps of 1/12 (.08333) are 1 semitone apart.

Up to three input CHOPs can be connected to the Oscillator CHOP.

Pitch Control - The first (optional) input affects the pitch. Output channels are generated for each Pitch Control channel. When pitch control is 0, it outputs a wave at the base frequency (default 440 Hz at 44,100 samples per second). It is "logarithmic": By default, increasing the pitch control by 1 increases the pitch by 1 octave, by 2 it increases by 2 octaves (3 times the frequency).

Reset Pulse - The second (optional) input contains pulses that restart the oscillator from the beginning of the wave or the Playback Source. 0 in the input means "play the oscillator". 1 means "stop the oscillator and cue it at the start of the waveform or Playback Source".

Playback Source - The third (optional) input is a replacement of the waveform Type. It is a sound clip to play at a rate modified by the Pitch Control, and can contain any number of channels. These channels are generated for each Pitch Control channel. The waveform Type and the Base Frequency parameters are disabled.

If you plug any sound clip into the Oscillator CHOP's Playback Source, and Pitch Control is a constant value of 0 of any duration, it will just repeat the Playback Source. If you feed a Wave CHOP as its Pitch Control, it will raise and lower the speed/pitch of the input.

The Oscillator CHOP can serve as a general motion time-warper and repeater. If you put motion channels into the third input, you can control the time warp by feeding different Pitch Control curves. 0 pitch is normal speed, 1 is double speed.

Unlike the Wave CHOP, this is an iterating CHOP, that is, it steps through the waveform while the pitch changes. To see this effect, feed a Wave CHOP into the Oscillator. Unlike the LFO CHOP, the Oscillator CHOP is designed for audio frequencies.

See also: LFO CHOP, Wave CHOP.

Parameters - Waveform Page

Type - The shape of the waveform to repeat, unless overridden by the Playback Source:

• Sine (-1 to 1)
• Gaussian (0 to 1)
• Triangle (-1 to 1)
• Ramp (0 to 1)
• Square (-1 to 1)
• Pulse (0 to 1)

Base Frequency /frequency - The cycles per second when the Pitch Control is zero.

Units per Octave /octave - Amount that the Pitch Control needs to increase by to raise the pitch by one octave. The default of 1 means that Pitch Control of 1 raises the pitch by 1 octave. Units per Octave of .08333 means that a Pitch Control of 3 raises the pitch by a factor of 3 x .08333 (three semitones). This is suitable for using MIDI note numbers as pitch control.

Offset /offset - Values output from the CHOP can have an offset added to them.

Amplitude /amp - Values output from the CHOP can be scaled.

Bias /bias - Shape control for Triangle, Gaussian and Square waves. For triangle waves, it moves the peak. For square waves, it alters the width of the peak. Zero means no bias.

Phase /phase - A value of .5 is a phase shift of 180 degrees, or one half cycle.

Reset - This button resets the channel(s) to 0.

Reset Condition - This menu determines how the Reset input triggers a reset of the channel(s).

• Off to On - channels are reset when the Reset input goes off to on.
• While On - channels are reset when the Reset input goes on. The channel will hold the reset value until the input turns off.
• On to Off - channels are reset when the Reset input goes on to off.
• While Off - channels are reset when the Reset input goes off. The channel will hold the reset value until the input turns on.

Smooth Pitch Changes - If the Pitch Control channel input to the Oscillator CHOP is rising and is running at the Touch default of 60 frames per second, then the pitch will hold for 1/60 second before stepping up for another 1/60 second. This is an audible step. With this option On, the pitch rises for every audio sample, giving perfectly smooth glissando at extra compute cost.

Parameters - Channel Page

Sample Rate - The sample rate of the CHOP. The default sample rate is 44100 Hz.

Standard Options and Local Variables

None.