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This CHOP filters an audio clip, and then applies other audio effects. The functions, in the order they are applied, are:
Parametric Filter - Filters any frequency range of the input.
Sideband Filter - Filters the input with another audio channel’s power spectrum (contained in the second input).
Pitch Shift - Shifts the pitch of an audio clip, maintaining the same duration.
Echo Generator - Adds echoes to the audio clip.
This CHOP may be time sliced to filter audio in realtime, though pitch shifting is not available in time slice mode.
Starred parameters (*) may be animated by the third input. These animation channels must be named the same as the control channel names.
The center frequency of the filter.
The bandwidth of the filter, in octaves.
The audio in the frequency range of the filter is multiplied by the Filter Gain.
The audio outside the frequency range of the filter is multiplied by the Pass Gain.
The shape of the filter. Zero is box,
.5 is triangular and
The dropoff factor of the filter shape.
Method to use when sideband filtering.
The power spectrum of a sideband filter can be used to enhance frequencies (Sideband Pass) or remove them (Sideband Stop).
The gain of the sideband filter.
The base gain of the channel.
The frequency effect of the filter.
Shifts the audio pitch up or down, expressed in octaves.
The chunk size at which Octave Shift resamples. Used to fine tune the sound once the correct pitch is found.
The number of echoes to generate before the sound occurs (not natural).
Pre Echo Delay
The amount of time between echoes.
Pre Echo Dropoff
The strength of the audio volume of the first pre-echo (other pre-echoes reduce by the same factor).
The number of echoes to generate after the sound has occurred.
Post Echo Delay
Same as Pre Echo Delay.
Post Echo Dropoff
Same as Pre Echo Dropoff.
See Remainder parameter in Copy or Trigger CHOPs.
Number of samples of input to process at a time for parametric and sideband filters.
The amount to overlap the chunks.
The amount of the chunk to discard.
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.
The current index.
The current channel (0 to NC-1).
The total number of channels.