# PHASEGeometricSpreadingDistanceModelParameters An object that dissipates sound frequencies over distance. ``` class PHASEGeometricSpreadingDistanceModelParameters ``` ## Overview This class implements a *roll-off* effect — a strategy that aims to model the real-world manner in which sound changes with distance. When the distance between a sound and listener changes, the roll-off effect dissipates certain audio frequencies more than others. ### Dissipate Sound by Choosing a Roll-Off Factor PHASE emphasizes or deemphasizes the volume loss of the mixer’s sound sources based on the [`rolloffFactor`](/documentation/PHASE/PHASEGeometricSpreadingDistanceModelParameters/rolloffFactor) you choose. For example, a [`rolloffFactor`](/documentation/PHASE/PHASEGeometricSpreadingDistanceModelParameters/rolloffFactor) of `1.0` reduces sound between the source and listener by 6 dB for every doubling of distance. At `2.0`, the loss doubles. At `0.5`, the loss halves. To add a geometric-spreading distance model to a spatial sounds, set the mixer’s [`distanceModelParameters`](/documentation/PHASE/PHASESpatialMixerDefinition/distanceModelParameters) property to an instance of this class. For example: ```swift let simpleModel = PHASEGeometricSpreadingDistanceModelParameters() simpleModel.rolloffFactor = 1.0 spatialMixer.distanceModelParameters = simpleModel ``` ## Topics ### Creating the Distance Model Parameters [`init()`](/documentation/PHASE/PHASEGeometricSpreadingDistanceModelParameters/init()) Creates the geometric spreading distance model parameters. ### Setting the Roll-Off Factor [`rolloffFactor`](/documentation/PHASE/PHASEGeometricSpreadingDistanceModelParameters/rolloffFactor) A value that fades specific frequencies over a distance. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)