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This CHOP is a 14-band equalizer which filters audio input channels in the same way that a conventional band equalizer uses a bank of sliders to filter fixed-frequency bands of sound.
The CHOP has 14 bands from 10Hz to 82kHz with one parameter per band. The 20Hz band ranges from 14 Hz to 28 Hz (1 octave centered at 20Hz). These bands may be be all shifted up or down in frequency with the Base Shift parameter. The shape of each band filter may also be specified as a Gaussian filter (smooth falloff, where the bands overlap) or a Box filter (sharp cutoff, where the bands don’t overlap).
The first input contains the channels to be filtered.
The second input contains optional channels called Filter Animation Channels, that override the frequency parameters of the CHOP. They replace the control channels in the CHOP dialog box (b10, b20…), and can be used to animate the filter parameters over the interval of the CHOP. To override a parameter with an Filter Animation Channel, it must have the exact same name as the parameter’s channel. To control the 40Hz band, the channel in the second input must be named “b40”.
Filter Animation Channels are evaluated at the beginning of every Filter Chunk that is processed. As the chunk size decreases, the rate at which your parameters can change increases, but the low frequency sound quality degrades. The first input and the second input should have the same start-end interval.
This CHOP can be time sliced to operate on audio in realtime.
The number of octaves to shift the bands up (positive values) or down (negative values). Each octave shifted up doubles each of the bands' frequencies.
Selects the band filter type to use. Gaussian produces a smooth filter, while Box produces a very sharp filter.
10, 20, 40
10, 20 and 40 Hz bands. /b10, b20, b40
80, 160, 320
80, 160 and 320 Hz bands. /b80, b160, b320
640 Hz and 1.28 kHz bands. /b640, b1k
2K, 5K, 10K
2.56, 5.12, 10.24 kHz bands. /b2k, b5k, b10k
20K, 41K, 82K
20.48, 40.96, 81.92 kHz bands. /b20k, b41k, b82k
The size of the chunk that is processed at one time, in samples.
The portion of the chunk to overlap with the previous one.
The portion 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.
Current evaluation index.
Current chunk being filtered.
Current channel being filtered.
Total number of channels.