Audiofiltering:

Improve filter performance by reducing frequency leakage.

cmd/audiofiltering/main.go

@@ -6,6 +6,7 @@ import(
 	"os"
 	"encoding/binary"
 	"github.com/mjibson/go-dsp/fft"
+	"github.com/mjibson/go-dsp/window"
 	"math/cmplx"
 	"time"
 	"sync"
@@ -36,7 +37,7 @@ func main() {
 	}
 	
 	// create filter
-	filterLen := 25
+	filterLen := 500
 	wg2.Add(1)
 	ch := make(chan []float64, 1)
 	go HighPass(filterLen, 2000, &wg2, ch)
@@ -55,12 +56,12 @@ func main() {
 	filter := <- ch
 
 	// convolve sinc with audio
-	wg1.Add(2)
+	wg1.Add(1)
-	go SaveAudioData(combinedAudio, "unfiltered", &wg1)
+	// go SaveAudioData(combinedAudio, "unfiltered", &wg1)
 	wg2.Add(1)
 	filteredAudio := Convolve(combinedAudio, filter, &wg2)
 	wg2.Wait()
-	go SaveAudioData(filteredAudio, "highpass", &wg1)
+	go SaveAudioData(filteredAudio, "highpass-2KHz", &wg1)
 	
 	wg1.Wait()
 	fmt.Println(time.Since(start))
@@ -100,29 +101,41 @@ func Max (a []float64) float64 {
 
 }
 
-func LowPass (n int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
+func LowPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
 
-	// n is number of points on either side of 0
-	// determine digital frequency equivalent for fc
-	fd := (fc*4)/(2*SampleRate)
 	// create sinc function
-	ch <- Sinc(n, fd)
+	size := taps + 1
+	fd := fc/SampleRate
+	b := (2*math.Pi) * fd
+	filter := make([]float64, size)
+	winData := window.FlatTop(size)
+	for n:=0; n<(taps/2); n++ {
+		c := float64(n) - float64(taps)/2
+		y := math.Sin(c*b) / (math.Pi * c)
+		filter[n] = y * winData[n]
+		filter[size-1-n] = filter[n]
+	}
+	filter[taps/2] = 2*fd*winData[taps/2]
+	ch <- filter
 	wg.Done()	
 
 }
 
-func HighPass (n int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
+func HighPass (taps int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
 
-	// n is number of points on either side of 0
-	// determine digital frequency equivalent for fc
-	fd := 0.5-((2*fc)/(SampleRate))
-	fmt.Println(fd)
 	// create sinc function
-	filter := Sinc(n, fd)
+	size := taps + 1
-	// convert lowpass to highpass filter
+	fd := fc/SampleRate
-	for i:=-n; i<=n; i++ {
+	b := (2*math.Pi) * fd
-		filter[i+n] = filter[i+n] * math.Pow(-1, float64(i))
+	filter := make([]float64, size)
+	winData := window.FlatTop(size)
+	for n:=0; n<(taps/2); n++ {
+		c := float64(n) - float64(taps)/2
+		y := math.Sin(c*b) / (math.Pi * c)
+		filter[n] = -y * winData[n]
+		filter[size-1-n] = filter[n]
 	}
+	filter[taps/2] = (1 - 2*fd) * winData[taps/2]
 	ch <- filter
 	wg.Done()	
 
@@ -130,11 +143,12 @@ func HighPass (n int, fc float64, wg *sync.WaitGroup, ch chan []float64) {
 
 func Convolve (x, h []float64, wg *sync.WaitGroup) []float64 {
 
-	convLen := len(x)+len(h)
+	// conv waitgroup
+	// var convwg sync.WaitGroup
+	convLen := len(x)+len(h)-1
 	y := make([]float64, convLen)
 	for n:=0; n<convLen; n++ {
-		wg.Add(1)
+			go func(n int, y []float64) {
-		go func (n int, x, h, y []float64, wg *sync.WaitGroup) {
 				var sum float64 = 0
 				for k:=0; k<len(x); k++ {
 					if n-k >= 0 && n-k < len(h) {
@@ -142,8 +156,8 @@ func Convolve (x, h []float64, wg *sync.WaitGroup) []float64 {
 					}
 				}
 			y[n] = sum
-			wg.Done()
+			} (n, y)
-		}(n, x, h, y, wg)
+			
 	}
 	wg.Done()
 	return y
@@ -160,6 +174,10 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
 	for i := range FFTaudio {
 		spectrum[i] = cmplx.Abs(FFTaudio[i])/float64(length)
 	}
+	// maximum := Max(signal)
+	// for i := range signal {
+	// 	signal[i] = signal[i]/maximum
+	// }
 	maximum := Max(spectrum)
 	for i := range spectrum {
 		spectrum[i] = spectrum[i]/maximum
@@ -170,8 +188,8 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
 	go func (fileName string, length int, spectrum []float64, wg1 *sync.WaitGroup) {
 		file := fileName + ".txt"
 		f, _ := os.Create(file)
-		for i:=0; i<20000; i++ {
+		for i:=0; i<len(spectrum)/2; i++ {
-			fmt.Fprintf(f, "%v\n", /*20*math.Log10*/(spectrum[i]))
+			fmt.Fprintf(f, "%v\n", 20*math.Log10(spectrum[i]))
 		}
 		fmt.Printf("Saved spectrum values to: %s\n", fileName)
 		wg1.Done()
@@ -181,8 +199,8 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
 		file := fileName + ".bin"
 		f, _ := os.Create(file)
 		var buf [8]byte
-		for i:=0; i<length; i++ {
+		for i:=0; i<len(signal); i++ {
-			binary.LittleEndian.PutUint32(buf[:], math.Float32bits(float32(signal[i])))
+			binary.LittleEndian.PutUint64(buf[:], math.Float64bits(signal[i]))
 			_, _ = f.Write(buf[:])
 		}
 		fmt.Printf("Saved binary values to: %s\n", fileName)
@@ -193,18 +211,26 @@ func SaveAudioData (signal []float64, fileName string, wg1 *sync.WaitGroup) {
 
 }
 
-func Sinc (nsamps int, fc float64) []float64 {
+// func SincRedundant (nsamps int, fc float64) []float64 {
 
-	// n is number of samples either side of n = 0
+// 	// n is number of samples either side of n = 0
-	h := make([]float64, nsamps*2 + 1)
+// 	h := make([]float64, nsamps*2 + 1)
-	for n:=-nsamps; n<=nsamps; n++ {
+// 	for n:=-nsamps; n<=nsamps; n++ {
-		if n == 0 {
+// 		if n == 0 {
-			h[n+nsamps] = 2*fc
+// 			h[n+nsamps] = 2*fc
-		} else {
+// 		} else {
-			h[n+nsamps] = math.Sin(2*math.Pi*fc*float64(n))/(math.Pi*float64(n))
+// 			h[n+nsamps] = math.Sin(2*math.Pi*fc*float64(n))/(math.Pi*float64(n))
-		}
+// 		}
-	}	
+// 	}	
 
-	return h
+// 	return h
 
-}
+// }
+
+// func Sinc (x float64) float64 {
+// 	if x == 0 {
+// 		return 
+// 	} else {
+// 		h[n+nsamps] = math.Sin(2*math.Pi*fc*float64(n))/(math.Pi*float64(n))
+// 	}
+// }