Expander

The Expander increases the dynamic range of a signal by weakening any part of the input signal that is below a pre-defined threshold value. When the signal is soft and below the threshold, the Expander begins to reduce the signal's gain. When the signal is at or louder than the threshold value, no gain reduction is applied to the signal.

A ratio factor determines the extent of the dynamic expansion when the input is below the threshold. For example, a ratio of 4 means that for every 4 dB the input signal is below the threshold, only 1 dB will be observed in the output signal.

To provide smooth transitions between the areas of gain reduction and no gain reduction, you can specify times for the attack and release properties. The attack time is the time it takes for the gain to be reduced when the input is below threshold. The release time is the time it takes for the signal to return to the threshold level where gain reduction is no longer applied.

The Expander plug-in contains a series of properties, many of which can be edited in real-time and can be mapped to specific Game Parameters using RTPCs.

You can use the Expander plug-in to reduce unwanted background noise. For example, you may need to reduce a low sounding background noise such as a hiss, so that other sounds could be heard more clearly. In some cases you can remove sounds from the output signal almost completely by setting a high expander ratio (over 10:1). This high ratio is known as a noise gate as it closes the gate for sounds whose gain has been reduced to this extent.

	Caution
	Sounds with a DC offset may alter the results of the Expander Effect. Make sure to remove the DC offset before applying the Expander Effect in Wwise. You can remove the DC offset before importing the audio file, or in Wwise when you convert the audio file.

Note

The following are some general remarks on Wwise dynamic processing plug-ins:

There is no interpolation of ratio control (RTPC parameter) for Compressor, Expander, or Peak Limiter. Changing this parameter during playback may lead to signal discontinuities on very clean signals.
Sounds with DC offset may alter results of compression/expansion because the sidechain detection algorithm will be offset considerably. DC offset should be removed prior to use in Wwise.
The Compressor, Expander, and Peak limiter are non-linear audio processes. This means that order of processing is important. For example, results will be different if you apply gain before or after the Effect.
For the first audio buffers, the processing algorithms are said to be in non-steady state. Because the estimated signal power operated by the side chain has no knowledge of the past, its estimate of signal power may be erroneous for a short period of time (but only if the Compressor is already engaged at the start of the sound). A solution to this (if it's a problem at all) is to start the Compressor with a ratio of 1 and shortly after bring it to the desired value.
If the Compressor applies some gain reduction and is suddenly bypassed, a signal discontinuity will be heard. A potential solution is to gradually bring the ratio to 1 prior to bypassing the Effect.

Using Expander on an Audio Objects bus

Applying a linear Effect, such as the Parametric EQ, to multiple Audio Objects independently is identical to applying it once to a downmix of those objects. Typically, this is not the case with non-linear Effects, such as compression or expansion. However, the Expander plug-in is a special type of Effect, called an Object Processor. When the Expander plug-in is inserted on an Audio Objects bus, the result is as follows:

The Effect is instantiated only once per bus instance, regardless of how many Audio Objects are routed to the bus.
It achieves the expansion of multiple Audio Objects together by working on an internal downmix, all while preserving the individual Audio Objects (that is, without mixing them down).
The gain reduction is common to all Audio Objects.
Expansion occurs implicitly in Channel Linked mode. Consequently, the Channel Link option is ignored.

Refer to Using Effects with Audio Objects for further details.

Expander properties

Interface Element

Description

Name

The name of the Effect instance.

Effect instances are a group of effect property settings. They can be one of two types: custom instances or ShareSets. Custom instances can be used by only one object, whereas ShareSets can be shared across several objects.

(Object Color)

Displays the object's color. Clicking the icon opens the color selector.

Select a color to apply it to the object. When you choose a color for an object, a palette icon appears on the selected square, as well as a yellow triangle in the lower-right corner, as shown.

To inherit the parent object's color, select the square at the far left of the color selector.

Inclusion

Determines whether the element is included in the SoundBanks when they are generated. When selected, the element is included. When unselected, the element is not included.

To optimize your sound design for each platform, you might want to exclude certain elements on certain platforms. By default, this check box applies across all platforms. Use the Link indicator to the left of the check box to unlink the element. Then you can customize the state of the check box per platform.

When this option is unselected, the property and behavior options in the editor become unavailable.

Default value: true

(Show references)

Indicates the number of elements in your project that contain direct references to the object. The icon is displayed in orange when references to the object exist, and in gray when no references exist.

Selecting the button opens the Reference View with the object's name in the References to: field.

Notes

Additional information about the Effect.

Metering

Indicates the name of the object currently being metered.

Allows you to browse for other objects to meter.

	Note
	The metering interface elements only appear in the Effect Editor for Effects that include VU meters.

Sets the display of the Effect Editor's selected tabs. By default, there is one panel displaying only one selected tab. You can, however, click a splitter button to split the panel into two, either side by side or one on top of the other, for two different tabs. The currently selected option is highlighted with a background color.

	Note
	You cannot display the same tab in both panels. If you select the tab that is currently displayed in the other panel, then the other panel will automatically display another tab.

Threshold	Specifies the point below which the expander will begin to process the signal and apply gain reduction. Default value: -40 Range: -96.3 to 0 Units: dB
Ratio	The representation of the amount of expansion that has been applied. A ratio of 2:1 indicates that the portion of the output level below the threshold will be further reduced by two times the value of the input. At a ratio of 10:1 and higher, you can create a noise gate. Default value: 3 Range: 1 to 50
Attack Time	The time it takes for the gain to be reduced when the input is below threshold. Default value: 0.1 Range: 0 to 2 Units: s
Release Time	The time it takes for the signal to return to the threshold level where gain reduction is no longer applied. Default value: 0.01 Range: 0 to 2 Units: s
Output Gain	The gain applied to the output level after the dynamic expansion. Default value: 0 Range: -24 to 24 Units: dB
Process LFE	Determines whether the Effect is processed in the LFE channel or not. When selected, the Effect is processed in the LFE channel. When unselected, the LFE channel will be unaffected. When selected, this option increases CPU usage even if there is no LFE signal in your pipeline. Default value: true
Channel Link	Applies the same gain reduction to all channels. This is implemented by taking the RMS power in the signal of all channels. The threshold is set by scaling the power in dB for the number of channels that are linked. If this option is not selected, no information is shared between channels, and the Effect is applied on a per-channel basis. Default value: true

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Expander

Expander

Using Expander on an Audio Objects bus

Expander properties

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