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Resample audio rather than adjusting parameters
Previously, attempted to adjust window size and overlap to handle different sampling rates, but this was error prone and imprecise. The frequency values would not line up. Instead, the new approach uses a generic resampler tool to resample audio. The current implementation only offers a very naive, but very fast linear interpolator.
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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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