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The Acoustic CHOP allows you to design audio filters and sound materials for the SpatialAudio 3D audio system.
Three different types of filters are available:
Describes which frequencies are transmitted (values close to 1) and which are absorbed by the material (values close to 0).
Describes which frequencies are reflected off the material. Currently reflections are not supported.
Describes which frequencies are absorbed by the filter (inverse of the transmission filter).
A sound material for a geometry object or a transmission filter requires either a transmission or absorption filter. A microphone filter requires an absorption filter.
When designing the filter, the CHOP graph should be in Frames mode, so that 1 frame on the graph equals 1KHz and frame 0 corresponds to 0Hz (DC). This means that frame 5.5 corresponds to 5.5kHz (5500Hz).
Filters cannot have negative values. If a filter has values of more than one, it will add power to that frequency (turn on No Resonance to avoid this). A value of 0.4 in a filter will reduce that frequency by 60%.
If checked, a transmission filter is created.
If checked, a reflection filter is created.
If checked, an absorption filter is created.
The frequency range of the filter(s).
Selects a power conservation method. Applicable when more than 1 filter is being designed.
No Power Conservation
Power can be reduced or amplified.
Conserve Total Power
Total power is conserved but the individual frequencies' power is not.
Conserve Power Per Frequency
Each frequency has its power conserved.
If power conservation is on, moving a handle on a filter will adjust the other filters. This parameter allows you to lock one of the filters.
Disallows filter values greater than 1.
The number of manipulation handles to create.
If on, the handles are logarithmically spaced, which is more useful than linear spacing (off) for designing audio filters.
The number of samples in each filter.
How the samples are interpolated from the handles; either nearest neighbor, linearly or cubically.
Reset All Waveforms
Resets all filters to a constant value.
Some of these parameters may not be available on all CHOP nodes.
To determine the channels that are affected, some CHOPs have a scope string. Patterns can be used in 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 the rate of the first input to resample the others.
Resample At Maximum Rate
Resample to the 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 of the time parameters.
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, the existing parameters are not converted to the new units.
Time slicing is a feature that boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel needs 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 the 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 to it for display in the graph, but you can override the color with the 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.