mirror of https://bitbucket.org/ausocean/av.git
Audiofiltering:
Implement bandpass filter by combining lowpass and highpass filters.
This commit is contained in:
ausocean-david
parent
49db1041d3
commit
75124b4494
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@ -12,7 +12,7 @@ import(
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"sync"
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)
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// define constants used in the generation of the sound waves
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// Define the constants to be used in the generation of the sound files.
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const(
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SampleRate float64 = 44100
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Duration = 2
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@ -20,12 +20,17 @@ const(
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length int = 88200
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)
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// main is a driver function which generates a sound file which contains sine waves from across the spectrum.
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// Filters can then be generated and applied to the audio, in order to test their frequency response.
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func main() {
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// Create waitgroups to ensure program runs correctly.
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var wg1, wg2 sync.WaitGroup
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// Take a measurement of the starting point of the program execution to use for execution timing.
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start := time.Now()
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// generate sine waves with different frequencies to test frequency response
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// Generate sine waves with different frequencies to test frequency response.
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n := 100
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wg1.Add(n)
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audio := make([][]float64, n)
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@ -36,14 +41,15 @@ func main() {
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} (i, audio, &wg1)
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}
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// create filter
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// Create the filter.
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filterLen := 500
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wg2.Add(1)
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ch := make(chan []float64, 1)
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go HighPass(filterLen, 2000, &wg2, ch)
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go BandPass(filterLen, 2000, 5000, &wg2, ch)
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// Combine all the generated sine waves into a single audio slice.
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wg1.Wait()
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// combine audio
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combinedAudio := make([]float64, length)
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for i := range audio[0] {
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combinedAudio[i] = 0
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@ -52,34 +58,41 @@ func main() {
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}
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}
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// Get the filter from the filter goroutine called earlier.
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wg2.Wait()
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filter := <- ch
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// convolve sinc with audio
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wg1.Add(1)
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// go SaveAudioData(combinedAudio, "unfiltered", &wg1)
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wg1.Add(2)
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// Save the unfiltered audio to compare the filtered audio against.
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go SaveAudioData(combinedAudio, "unfiltered", &wg1)
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// Apply the filter to the combined audio file by computing the convolution of the 2 slices.
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wg2.Add(1)
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filteredAudio := Convolve(combinedAudio, filter, &wg2)
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wg2.Wait()
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go SaveAudioData(filteredAudio, "highpass-2KHz", &wg1)
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// Save the filtered audio.
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wg2.Wait()
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go SaveAudioData(filteredAudio, "bandpass-2-5KHz", &wg1)
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// Print the total time of execution, to compare different algorithms.
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wg1.Wait()
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fmt.Println(time.Since(start))
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}
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// generate is used to generate a sine wave of the given frequency, calls on the global variables of Duration and SampleRate
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func generate(Frequency float64) []float64 {
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// deteremine number of samples based off duration and sample rate
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// Deteremine the number of samples required based off Duration and SampleRate.
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nsamps := Duration * SampleRate
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// generate x-values
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// Generate the x-values to plot against.
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var angle float64 = tau / float64(nsamps)
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// create sample array
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// Create an array for the generated samples.
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samp := make([]float64, int(nsamps))
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// generate samples and write to file
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// Generate the samples.
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for i := 0; i < int(nsamps); i++ {
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samp[i] = math.Sin(angle * Frequency * float64(4*i))
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}
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@ -88,7 +101,8 @@ func generate(Frequency float64) []float64 {
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}
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func Max (a []float64) float64 {
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// max returns the absolute highest value in a given array.
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func max(a []float64) float64 {
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var runMax float64 = -1
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for i:= range a {
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@ -101,9 +115,10 @@ func Max (a []float64) float64 {
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}
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// LowPass returns an array of coeffiecients over the given channel that can be used in a convolution with a signal to perform
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// a lowpass filtering with the given cut-off frequency fc.
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func LowPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
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// create sinc function
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size := taps + 1
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fd := fc/SampleRate
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b := (2*math.Pi) * fd
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@ -121,9 +136,10 @@ func LowPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
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}
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// HighPass returns an array of coeffiecients over the given channel that can be used in a convolution with a signal to perform
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// a highpass filtering with the given cut-off frequency fc.
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func HighPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
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// create sinc function
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size := taps + 1
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fd := fc/SampleRate
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b := (2*math.Pi) * fd
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@ -141,14 +157,47 @@ func HighPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
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}
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// BandPass returns an array of coeffiecients over the given channel that can be used in a convolution with a signal to perform
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// a bandpass filtering with the given lower and upper cutoff frequencies (using the low and highpass filter functions).
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func BandPass (taps int, lower, upper float64, wg *sync.WaitGroup, ch chan []float64) {
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// Create a waitgroup and channel to be used internally within the function.
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var bpwg sync.WaitGroup
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bpch := make(chan []float64, 2)
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// Call low and highpass filter functions.
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filters := make([][]float64, 2)
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bpwg.Add(2)
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go LowPass(taps, upper, &bpwg, bpch)
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go HighPass(taps, lower, &bpwg, bpch)
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bpwg.Wait()
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for i:=0; i<2; i++ {
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filters[i] = <- bpch
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}
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// Convolve lowpass filter with highpass filter to get bandpass filter.
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bpwg.Add(1)
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bpFilter := Convolve(filters[0], filters[1], &bpwg)
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ch <- bpFilter
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wg.Done()
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}
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// Convolve returns the real convolution of the 2 given arrays.
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func Convolve (x, h []float64, wg *sync.WaitGroup) []float64 {
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// conv waitgroup
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// var convwg sync.WaitGroup
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// Create a waitgroup to be used in goroutines called by Convolution
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var convwg sync.WaitGroup
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// Compute the convolution
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convLen := len(x)+len(h)-1
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y := make([]float64, convLen)
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for n:=0; n<convLen; n++ {
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go func(n int, y []float64) {
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convwg.Add(1)
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go func(n int, y []float64, wg *sync.WaitGroup) {
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var sum float64 = 0
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for k:=0; k<len(x); k++ {
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if n-k >= 0 && n-k < len(h) {
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@ -156,34 +205,31 @@ func Convolve (x, h []float64, wg *sync.WaitGroup) []float64 {
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}
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}
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y[n] = sum
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} (n, y)
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wg.Done()
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} (n, y, &convwg)
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}
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wg.Done()
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return y
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}
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// SaveAudioData takes an input signal and filename and saves the frequency spectrum (to .txt) and the audio signal (to .bin).
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func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
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// compute fft of signal
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// Compute the FFT of the signal
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FFTaudio := fft.FFTReal(signal)
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// normalise and save signal
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// Normalise the frequency response (-1:1).
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spectrum := make([]float64, len(signal))
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for i := range FFTaudio {
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spectrum[i] = cmplx.Abs(FFTaudio[i])/float64(length)
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}
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// maximum := Max(signal)
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// for i := range signal {
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// signal[i] = signal[i]/maximum
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// }
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maximum := Max(spectrum)
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maximum := max(spectrum)
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for i := range spectrum {
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spectrum[i] = spectrum[i]/maximum
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}
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// SAVE
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// Save the frequency response/spectrum.
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wg1.Add(2)
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go func (fileName string, length int, spectrum []float64, wg1 *sync.WaitGroup) {
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file := fileName + ".txt"
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@ -195,6 +241,7 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
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wg1.Done()
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}(fileName, 44100, spectrum, wg1)
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// Save the audio file.
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go func (fileName string, signal []float64, wg1 *sync.WaitGroup) {
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file := fileName + ".bin"
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f, _ := os.Create(file)
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@ -209,28 +256,4 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
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wg1.Done()
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}
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// func SincRedundant (nsamps int, fc float64) []float64 {
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// // n is number of samples either side of n = 0
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// h := make([]float64, nsamps*2 + 1)
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// for n:=-nsamps; n<=nsamps; n++ {
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// if n == 0 {
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// h[n+nsamps] = 2*fc
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// } else {
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// h[n+nsamps] = math.Sin(2*math.Pi*fc*float64(n))/(math.Pi*float64(n))
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// }
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// }
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// return h
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// }
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// func Sinc (x float64) float64 {
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// if x == 0 {
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// return
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// } else {
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// h[n+nsamps] = math.Sin(2*math.Pi*fc*float64(n))/(math.Pi*float64(n))
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// }
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// }
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}
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