# init(previousDFT:count:direction:transformType:ofType:) Initializes a new discrete Fourier transform structure. ``` init(previousDFT: vDSP.DiscreteFourierTransform?, count: Int, direction: vDSP.FourierTransformDirection, transformType: vDSP.DFTTransformType, ofType: T.Type) throws ``` ## Parameters `previousDFT` A previous DFT instance to share data with. `count` The number of complex elements. `transformType` Specifies whether the forward transform is real-to-complex or complex-to-complex. ## Discussion The `count` parameter must be: - For split-complex real-to-complex: `2ⁿ` or `f * 2ⁿ`, where `f` is `3`, `5`, or `15` and `n >= 4`. - For split-complex complex-to-complex: `2ⁿ` or `f * 2ⁿ`, where `f` is `3`, `5`, or `15` and `n >= 3`. - For interleaved: `f * 2ⁿ`, where `f` is `2`, `3`, `5`, `3x3`, `3x5`, or `5x5`, and `n>=2`. --- 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)