Parametric EQ channel node

Filters an audio clip, and then applies other audio effects.

All

Parameters

Local variables

This CHOP filters an audio clip, and then applies other audio effects. The functions, in the order they are applied, are:

Parametric Filter - Filters any frequency range of the input.
Sideband Filter - Filters the input with another audio channel’s power spectrum (contained in the second input).
Pitch Shift - Shifts the pitch of an audio clip, maintaining the same duration.
Echo Generator - Adds echoes to the audio clip.

This CHOP may be time sliced to filter audio in realtime, though pitch shifting is not available in time slice mode.

Starred parameters (*) may be animated by the third input. These animation channels must be named the same as the control channel names.

Parameters

Filter

Center Frequency*	The center frequency of the filter.
Bandwidth*	The bandwidth of the filter, in octaves.
Filter Gain*	The audio in the frequency range of the filter is multiplied by the Filter Gain.
Pass Gain*	The audio outside the frequency range of the filter is multiplied by the Pass Gain.
Filter Shape*	The shape of the filter. Zero is box, `.5` is triangular and `1` is Gaussian.
Filter Dropoff*	The dropoff factor of the filter shape.

Sideband

Sideband Filter	Method to use when sideband filtering.
Filter Type	The power spectrum of a sideband filter can be used to enhance frequencies (Sideband Pass) or remove them (Sideband Stop).
Sideband Gain	The gain of the sideband filter.
Base Gain	The base gain of the channel.
Sideband Effect	The frequency effect of the filter.

Pitch

Octave Shift*	Shifts the audio pitch up or down, expressed in octaves.
Pitch Chunk	The chunk size at which Octave Shift resamples. Used to fine tune the sound once the correct pitch is found.

Echo

Pre Echoes	The number of echoes to generate before the sound occurs (not natural).
Pre Echo Delay	The amount of time between echoes.
Pre Echo Dropoff	The strength of the audio volume of the first pre-echo (other pre-echoes reduce by the same factor).
Post Echoes	The number of echoes to generate after the sound has occurred.
Post Echo Delay	Same as Pre Echo Delay.
Post Echo Dropoff	Same as Pre Echo Dropoff.
Remainder	See Remainder parameter in Copy or Trigger CHOPs.

Digital

Filter Chunk	Number of samples of input to process at a time for parametric and sideband filters.
Chunk Overlap	The amount to overlap the chunks.
Chunk Discard	The amount of the chunk to discard.

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	The current index.
C	The current channel (0 to NC-1).
NC	The total number of channels.

Usages in other examples

Example name	Example for