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This CHOP filters audio input using one of four different filter types. Incoming channels are broken into chunks that overlap in time.
The second input is the Filter Animation Channels, which allows the filter parameters to be changed over the CHOP’s interval. See the Band EQ CHOP help, or the section in the Common Options of CHOPs called Filter Animation Channels Input.
This CHOP may be time sliced to filter audio in realtime.
See the Pass Filter CHOP section in the Houdini manual for explanation of filter terminology.
Low Pass Filter
All frequencies below the High Cutoff are passed through the filter (the “pass band”).
High Pass Filter
All frequencies above the Low Cutoff are passed through.
Band Pass Filter
All frequencies between the Low and High Cutoff are passed through.
Band Stop Filter
All frequencies above the High Cutoff and below the Low Cutoff are passed though.
Type of filter design to use:
The default filter design.
Filter which has maximally flat magnitude in the passband. Only available for low pass and high pass filters.
Order of the filter. Only used by Butterworth filters.
The frequency (in Hertz) of the lower cutoff. This value is not used by a low pass filter.
The frequency (in Hertz) of the upper cutoff. This value is not used by a high pass filter.
Pass Gain (dB)
The gain of passed frequencies, specified in dB (decibels). Every increase of 20dB corresponds to a 10-times power increase.
How the filter drops off at the cutoff frequencies. Low values (less than one) produce more gradual rolloff, and higher values produce sharper filters.
Also Filter Phase
Normally, the magnitude of the signal is filtered. You can optionally filter the phase of the signal.
This parameter allows you to select the chunk size, to balance the demands of animating filter parameters with the quality of sound.
How much of the current chunk is overlapped and blended with
the previous chunk. From zero (no overlap and blending) to
.95 (95% overlapped). Keep between
.3. Values too
close to zero will not entirely remove the discontinuity.
The chunk to throw away. Since the middle section is most
accurate, the end sections are discarded. From zero (don’t
discard anything) to
.95 (keep only the middle 5%). Normally
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.
Current evaluation index.
Current chunk being filtered.
Current channel being filtered.
Total number of channels.