# PHASEEnvelope A collection of segments that connect to graph a complex curve over a linear input. ``` class PHASEEnvelope ``` ## Overview In traditional audio uses, an *envelope* defines a complex graph that determines the volume of audio data over an input duration. PHASE uses envelopes in a similar way. Given a value on the envelope’s input axis, the [`evaluate(x:)`](/documentation/PHASE/PHASEEnvelope/evaluate(x:)) function plots and returns the result on the output axis. The following are possible uses of this class: - Sound event nodes, such as [`PHASEBlendNodeDefinition`](/documentation/PHASE/PHASEBlendNodeDefinition), can shape their volume using an envelope; see [`addRange(envelope:subtree:)`](/documentation/PHASE/PHASEBlendNodeDefinition/addRange(envelope:subtree:)). - Distance models shape sounds with a 3D position using an envelope; see [`PHASEEnvelopeDistanceModelParameters`](/documentation/PHASE/PHASEEnvelopeDistanceModelParameters). - An envelope can do more than shape audio. To gradually change an envelope’s input value over time, use the [`PHASEMappedMetaParameterDefinition`](/documentation/PHASE/PHASEMappedMetaParameterDefinition) class, which creates a function with a metaparameter value as input. An app can use the numeric result for any purpose. For example, the x-axis can be distance and the y-axis can be playback rate. At runtime, PHASE determines whether a particular member of the [`segments`](/documentation/PHASE/PHASEEnvelope/segments) array slopes up or down along the domain depending on the envelope’s particular use case. ### Create an Envelope and Shape its Curve To use an envelope in your app, define its shape by defining a series of segments. Each segment specifies a curve that collectively connect to form a graph. The following code creates an envelope with a single segment that’s shaped like the lettter *s:* ```objc // Create a segments array. NSMutableArray* segments = [NSMutableArray new]; // Create a single segment with a sigmoid curve to give "ease in, // ease out" movement along the domain. Define an endpoint of (1, 1). PHASEEnvelopeSegment* segment = [[PHASEEnvelopeSegment alloc] initWithEndPoint:simd_make_double2(1.0, 1.0) curveType:PHASECurveTypeSigmoid]; // Add the segment to the array. [segments addObject:segment]; // Create the envelope and set the start point to (-1, -1). PHASEEnvelope* envelope = [[PHASEEnvelope alloc] initWithStartPoint:simd_make_double2(-1.0, -1.0) segments:segments]; ``` The graph flexes at runtime depending on the source content on which the envelope operates. A [`PHASEEnvelope`](/documentation/PHASE/PHASEEnvelope) doesn’t constrain the [`evaluate(x:)`](/documentation/PHASE/PHASEEnvelope/evaluate(x:)) function’s output to predertermined values. Instead, PHASE applies the envelope’s curves to the source content as a rate of change. ## Topics ### Creating an Envelope [`- initWithStartPoint:segments:`](/documentation/PHASE/PHASEEnvelope/init(startPoint:segments:)) Creates an envelope with a start point and segments. ### Inspecting the Envelope [`- evaluateForValue:`](/documentation/PHASE/PHASEEnvelope/evaluate(x:)) Provides the height of the envelope for an input value. [`segments`](/documentation/PHASE/PHASEEnvelope/segments) An array of the envelope’s segments. [`startPoint`](/documentation/PHASE/PHASEEnvelope/startPoint) The starting point along the envelope’s duration. ### Bounding the Input [`domain`](/documentation/PHASE/PHASEEnvelope/domain) The range of the envelope’s possible input values. [`range`](/documentation/PHASE/PHASEEnvelope/range) The bounds of the output value. ## Relationships ### Conforms To [`Hashable`](/documentation/Swift/Hashable) [`Equatable`](/documentation/Swift/Equatable) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`CVarArg`](/documentation/Swift/CVarArg) [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) ### Inherits From [`NSObject-swift.class`](/documentation/ObjectiveC/NSObject-swift.class) --- 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)