Pass Filter channel node

Filters audio input using one of four different filter types.

All

Parameters

Local variables

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 popup 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.

Parameters

Filter

Filter type:

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.

Low Cutoff

The frequency (in Hertz) of the lower cutoff. This value is not used by a low pass filter.

High Cutoff

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.

Rolloff Factor

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.

Digital

Filter Chunk	This parameter allows you to select the chunk size, to balance the demands of animating filter parameters with the quality of sound.
Chunk Overlap	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 `.05` to `.3`. Values too close to zero will not entirely remove the discontinuity.
Chunk Discard	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 discard between `.05` and `.2`.

Common

Some of these parameters may not be avaiable on all CHOP nodes.

Scope

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:

`chan2`	Matches a single channel name.
`chan3 tx ty tz`	Matches four channel names, separated by spaces.
`chan*`	Matches each channel that starts with `chan`.
`foot`	Matches each channel that has `foot` in it.
`t?`	The `?` matches a single character. `t?` matches two-character channels starting with t.
`r[xyz]`	Matches channels `rx`, `ry` and `rz`.
`blend[3-7:2]`	Matches number ranges giving `blend3`, `blend5`, and `blend7`.
`blend[2-3,5,13]`	Matches channels `blend2`, `blend3`, `blend5`, `blend13`.
`t[xyz]`	`[xyz]`matches three characters, giving channels `tx`, `ty` and `tz`.

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.

Units

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).

Note

When you change the Units parameter, it does not convert the existing parameters to the new units.

Time Slice

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.

Unload

Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.

Export Prefix

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 /obj/geo1/tx.

Note

You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as obj:geo1:tx.

Graph Color

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.

Local variables

I	Current evaluation index.
N	Current chunk being filtered.
C	Current channel being filtered.
NC	Total number of channels.

Usages in other examples

Example name	Example for