Houdini 11 Nodes Channel nodes

Receives audio input from the analog audio ports or the digital port.

This CHOP receives audio input from the analog audio ports or the digital port. It always outputs time sliced audio data. If you want to record the data, use a Record CHOP.


Receiving audio from an audio CD using a CD-ROM is not supported. Instead, feed the audio through the Audio-in port.



Audio Source

Selects the audio port to listen to.


Listens to the analog microphone port.


Listens to the analog line in port.


Listens to the digital port.

Audio Format

Selects mono, stereo, or 4 channel mode. 4 Channel mode is not available on all systems. This parameter also determines how many channels are created (1, 2 or 4).

Use Global Sample Rate

If on, audio is sampled at the system input sample rate. Otherwise, the next parameter allows you to change the system input sample rate.


This may disrupt other applications using the audio system. This parameter does not set the actual channel sample rate; that is set by the Sample Rate parameter in the Channel tab. These two sample rates can differ; the audio is resampled to the channel sample rate.

Input Sample Rate

The sample rate of the audio input system.

Record Queue

The number of seconds of audio to buffer at the input. Input audio will be delayed by this amount of time. A large buffer allows for slower cooking; if the buffer is too small, gaps and pops will be heard in the audio.


Channel 1-4

Each channel can be scaled separately by any factor.

Input Attenuation

This parameter controls the audio system hardware’s input attenuation, which corresponds to the “record level” of a tape recorder. 0 is the lowest recording level, and 1 is the highest recording level. If you notice audio is being clipped at +-1, lower this value.


Channel 1-4 Name

The names of the audio channels.

Sample Rate

The sample rate of the audio channels. This may be different from the audio input’s sample rate; the input audio will be resampled to the CHOP’s sample rate.

Extend Left, Right

The extend conditions for the audio channels.

Default Value

The default value for the 'Default Value' extend condition.


Some of these parameters may not be avaiable 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 chan.

Matches each channel that has foot in it.


The ? matches a single character. t? matches two-character channels starting with t.


Matches channels rx, ry and rz.


Matches number ranges giving blend3, blend5, and blend7.


Matches channels blend2, blend3, blend5, blend13.


[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.


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 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.


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.


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.

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