Spatial Audio channel node

The rendering engine for producing 3D audio.

See also: Acoustic, Sound, Microphone

The Spatial Audio CHOP is the rendering engine for producing 3D audio. It uses the Sound and Microphone objects to define positional sources and microphones, Geometry objects to define obstructions and Acoustic CHOPs to define sound materials and audio filters.

The first input is an optional lookup table for the volume dropoff over distance. This is required if the Distance Volume Loss parameter is set to Distance/Volume Lookup Table. The second input is an optional 'Environment Filter' which describes how the environment affects the frequencies of sound traveling through it (used with the Distance Volume Loss parameter).

Parameters

Environment

Microphones	Specifies the microphone objects to use. One channel is created per microphone.
Sound Sources	Specifies the sound objects to use.
Meters Per Unit	Length of 1 world unit, in meters.
Speed of Sound	The speed of sound of the environment, in meters per second (default speed is for air).

Effects

Enable Distance Delay

Enables delays over long distances, as well as the doppler effect (realistic if on).

Distance Volume Loss

Method for calculating volume loss over distance.

None	Distance does not diminish sound.
Realistic Distance Dropoff	Natural volume dropoff `(1/d^2)`.
Distance/Volume Lookup Table	Determine from the lookup table connected to the first input.

10m Volume Loss

How much volume is decreased after traveling 10 meters (.4=40% decrease).

Volume Lookup Range

The range of the distance lookup table; (10,100) means that the table describes how the volume behaves from 10-100 meters.

Use Microphone Filters

Enables or disables all microphone filters.

Check For Obstacles

Turns on the algorithm for obstacle occlusion.

Obstacles

Add geometry objects as an obstacles. The sound material for these object must be defined. The geometry detail should be low.

Collision Detection

Specifies the collision detection algorithm.

Object Bounding Box	Uses the bounding box of the entire object as the collision object (very fast).
Primitive Bounding Box	Uses a bounding box per primitive. Good for objects that consist of separate geometries.
Object Geometry	Uses the actual geometry as the collision object (slowest & most accurate).

Obstacle Softness

If an object is between a microphone and a sound source, this parameter determines how abruptly the cutoff is (0 = abrupt, 1 = smooth).

Echo

Echo Method	Computes static or dynamic environmental echoes.
Number of Echoes	The number of echoes to compute.
Echo Delay	The time between echoes.
Echo Volume	Adjusts the volume of all echoes.
Dynamic Echo Effect	Percentage longer that echoes take to arrive than the initial sound (.5 = 50% longer)

Channel

Compute Full Animation Range	Compute using the full animation range, otherwise use the start/end parameters.
Preroll	The amount computed before the start of the interval.
Object Sample Rate	The rate that object are sampled at.
Audio Sample Rate	The sample rate of the audio produced.

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.

Usages in other examples

Example name	Example for