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Merge pull request #12 from nathanntg/resample
Resample audio rather than adjusting parameters
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,81 @@ | ||
| // | ||
| // Resampler.swift | ||
| // SyllableDetector | ||
| // | ||
| // Created by Nathan Perkins on 1/5/16. | ||
| // Copyright © 2016 Gardner Lab. All rights reserved. | ||
| // | ||
|
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| import Foundation | ||
| import Accelerate | ||
|
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| protocol Resampler { | ||
| func resampleVector(data: UnsafePointer<Float>, ofLength numSamples: Int) -> [Float] | ||
| // func resampleVector(data: UnsafePointer<Float>, ofLength numSamples: Int, toOutput: UnsafeMutablePointer<Float>) -> Int | ||
| } | ||
|
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| // potentially use: http://www.mega-nerd.com/SRC/api_misc.html#Converters | ||
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| /// Terrible quality, very fast. | ||
| class ResamplerLinear: Resampler { | ||
| let samplingRateIn: Double | ||
| let samplingRateOut: Double | ||
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| private let step: Float | ||
| private var last: Float = 0.0 // used for interpolating across samples | ||
| private var offset: Float = 0.0 | ||
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| init(fromRate samplingRateIn: Double, toRate samplingRateOut: Double) { | ||
| self.samplingRateIn = samplingRateIn | ||
| self.samplingRateOut = samplingRateOut | ||
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| self.step = Float(samplingRateIn / samplingRateOut) | ||
| } | ||
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| func resampleVector(data: UnsafePointer<Float>, ofLength numSamplesIn: Int) -> [Float] { | ||
| // need to interpolate across last set of samples | ||
| let interpolateAcross = (offset < 0) | ||
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| // expected number of samples from current | ||
| let numSamplesOut = Int((Float(numSamplesIn) - offset) / step) | ||
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| // return list | ||
| var ret = [Float](count: numSamplesOut, repeatedValue: 0.0) | ||
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| // indices | ||
| let indices = UnsafeMutablePointer<Float>.alloc(numSamplesOut) | ||
| var t_offset = offset, t_step = step | ||
| defer { | ||
| indices.destroy() | ||
| indices.dealloc(numSamplesOut) | ||
| } | ||
| vDSP_vramp(&t_offset, &t_step, indices, 1, vDSP_Length(numSamplesOut)) | ||
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| if interpolateAcross { | ||
| indices[0] = 0.0 | ||
| } | ||
|
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| // interpolate | ||
| vDSP_vlint(data, indices, 1, &ret, 1, vDSP_Length(numSamplesOut), vDSP_Length(numSamplesIn)) | ||
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| if interpolateAcross { | ||
| ret[0] = (last * (0 - offset)) + (data[0] * (1 + offset)) | ||
| } | ||
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| offset = indices[numSamplesOut - 1] + step - Float(numSamplesIn - 1) | ||
| last = data[numSamplesIn - 1] | ||
| //print("\(indices[numSamplesOut - 1]) \(numSamplesIn) \(offset)") | ||
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| return ret | ||
| } | ||
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| func resampleArray(var arr: [Float]) -> [Float] { | ||
| // used for testing | ||
| return self.resampleVector(&arr, ofLength: arr.count) | ||
| } | ||
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| // func resampleVector(data: UnsafePointer<Float>, ofLength numSamples: Int, toOutput: UnsafeMutablePointer<Float>) -> Int { | ||
| // | ||
| // } | ||
| } | ||
|
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