# channelCapabilities Expresses valid combinations of input and output channels. ``` var channelCapabilities: [NSNumber]? { get } ``` ## Discussion Array elements are values containing integers. The array index alternates between input and output counts, in ascending order of input/output channels—for example: [0] = first input count, [1] = first output count, [2] = second input count, [3] = second output count, etc. Positive array values specify the number of input and/or output channels supported. Negative array values have particular meanings. An input/output value pair of `(-1, -1)` (i.e. [0] = -1, [1] = -1) indicates that any number of channels are supported, as long as they are the same number for both input and output. An input/output value pair combination of `-1` and `-2` (e.g. [0] = -1, [1] = -2) also indicates that any number of channels are supported, but without the requirement that the input and output counts are the same. A negative value less than `-2` (e.g. [0] = -16) specifies a total number of channels across every bus in that scope, regardless of how many channels are set on any particular bus. An array value of `0` (e.g. [0] = 0) specifies that the input/output channel is not applicable (though typically only used for input channels). The table below shows a sample selection of valid input and output channel combinations: |Array Index |Integer Value |Meaning | |---------------------|-----------------|------------------------------------------------------------------------------------------------------------------------------------------| |[0]  [1] |-1  -1|First input/output count.  Any number of input and output channels, requiring that the numbers match. This is the default case.| |[2]  [3] |-1  -2|Second input/output count.  Any number of input and output channels, without requiring that the numbers match. | |[4]  [5] |2  6 |Third input/output count.  Exactly two input channels, exactly six output channels. | |[6]  [7] |-1  2 |Fourth input/output count.  Any number of input channels, exactly two output channels. | |[8]  [9] |0  1 |Fifth input/output count.  No input channels, exactly one output channel. | |[10]  [11]|-4  -8|Sixth input/output count.  Up to four input channels, up to eight output channels. | This version 3 property is bridged to the version 2 `kAudioUnitProperty_SupportedNumChannels` API. --- 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)