This CHOP calculates the frequency spectrum of the input channels, or a portion of the channels. The spectrum can be manipulated and then converted back to get a filtered signal.
When converting a signal to its spectrum, two channels are created from the one containing the signal. One channel contains the magnitude of the frequency components, and the other contains the phase. The channels are named <channel name><suffix>, where <suffix> is the magnitude or phase suffix.
In order to convert back to a signal, both channels are required. The suffixes should be the same as those used in the previous spectrum CHOP.
Determines whether to calculate the frequency spectrum from a signal, or reconstruct a signal from a frequency spectrum.
If on, only a small segment of the channel is analyzed. If off, the spectrum is computed from the entire channel.
Determines how Start/End parameters are interpreted.
The segment is the start/end values.
Relative to Start/End
The segment is a shift from the old positions of the input’s start/end.
Relative to Current Frame
The segment is a shift from the current frame.
Determines the start of the segment to be analyzed (in Units).
Determines the end of the segment to be analyzed (in Units).
When converting to a spectrum, the string appended to the channel name that identifies the channel as containing magnitudes.
Similar to Magnitude Suffix, but for phase channels.
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.