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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.
When it is synthesizing tones from the basic waveforms, it 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
-1 gives 220 Hz. Steps of
1 in Pitch Control are 1 octave apart.
1/12 (.08333) are 1 semitone apart.
Up to three input chops can be used.
The first input affects the pitch. (It is "logarithmic".) Output channels are generated for each Pitch Control channel.
The second (optional) input contains pulses that restart the
oscillator from the beginning of the wave or the Playback Source.
in the input means "play the oscillator".
1 means "stop the
oscillator and cue it at the start of the waveform or Playback
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
The Oscillator CHOP can serve as a general motion time-warper. If
you put motion channels into the third input, you can control the
time warp by feeding different Pitch Control curves.
0 pitch is
1 is double speed.
Unlike the Waveform 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.
The shape of the waveform to repeat. Sine, Gaussian, Triangle, Ramp, Square, Pulse
Cycles per second when Pitch Control is 0.
Units per Octave
Amount that the Pitch Control needs to increase by to raise the pitch by one octave. The default of 1 means that a Pitch Control of 1 raises the pitch by one octave.
Values output from the CHOP can have an added to them.
Values output from the CHOP can be scaled.
Shape control for Triangle, Gaussian and Square waves. For triangle waves, it moves the peak. For square waves, it alters the width.
A value of .5 is a phase shift of 180 degrees, or one half cycle.
Smooth Pitch Changes
Samples the pitch curve for every sample between frames vs. using a single per-frame value.
The sample rate of the CHOP.
Some of these parameters may not be available on all CHOP nodes.
To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example
* (match all), and
? (match single character).
The following are examples of possible channel name matching options:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
Sample Rate Match
The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.
Resample At First Input’s Rate
Use rate of first input to resample others.
Resample At Maximum Rate
Resample to highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
The units for which time parameters are specified.
For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).
When you change the Units parameter, it does not convert the existing parameters to the new units.
Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
The Export prefix is prepended to CHOP channel names to determine where to export to.
For example, if the CHOP channel was named
geo1:tx, and the prefix was
/obj, the channel would be exported to
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.
Graph Color Step
When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.