Add Phaser and Noise wave forms

Author: elgopher

audio/internal.go

@@ -27,6 +27,10 @@ func oscillatorFunc(instrument Instrument) func(float64) float64 {
 		return internal.Pulse
 	case InstrumentOrgan:
 		return internal.Organ
+	case InstrumentNoise:
+		return internal.Noise()
+	case InstrumentPhaser:
+		return internal.Phaser
 	default:
 		return silence
 	}

audio/internal/oscillator.go

@@ -3,7 +3,10 @@
 
 package internal
 
-import "math"
+import (
+	"math"
+	"math/rand"
+)
 
 type Oscillator struct {
 	Func   func(pos float64) float64
@@ -19,13 +22,15 @@ func (o *Oscillator) NextSample() (v float64) {
 }
 
 func Triangle(pos float64) float64 {
+	// Based on https://github.com/picolove
 	phase := math.Mod(pos, 1)
 	value := math.Abs(phase*2-1)*2 - 1
 
 	return value * 0.45
 }
 
 func TiltedSaw(pos float64) float64 {
+	// Based on https://github.com/picolove
 	phase := math.Mod(pos, 1)
 	var v float64
 	if phase < 0.875 {
@@ -37,11 +42,13 @@ func TiltedSaw(pos float64) float64 {
 }
 
 func Saw(pos float64) float64 {
+	// Based on https://github.com/picolove
 	phase := math.Mod(pos, 1)
 	return (phase - 0.5) * 0.65
 }
 
 func Square(pos float64) float64 {
+	// Based on https://github.com/picolove
 	phase := math.Mod(pos, 1)
 	v := -1.0
 	if phase < 0.5 {
@@ -51,6 +58,7 @@ func Square(pos float64) float64 {
 }
 
 func Pulse(pos float64) float64 {
+	// Based on https://github.com/picolove
 	phase := math.Mod(pos, 1)
 	v := -1.0
 	if phase < 0.3125 {
@@ -61,10 +69,38 @@ func Pulse(pos float64) float64 {
 
 // Organ is triangle / 2
 func Organ(pos float64) float64 {
+	// Based on https://github.com/picolove
 	pos = pos * 4
 
 	v := math.Abs(math.Mod(pos, 2)-1) - 0.5 +
 		(math.Abs((math.Mod(pos*0.5, 2))-1)-0.5)/2 - 0.1
 
 	return v * 0.55
 }
+
+func Noise() func(pos float64) float64 {
+	// Based on https://github.com/picolove
+	lastPos := 0.0
+	sample := 0.0
+	lsample := 0.0
+	const tscale = 2489.0158697766 / SampleRate // 2489.0158697766 is freq for D#5
+
+	return func(pos float64) float64 {
+		scale := (pos - lastPos) / tscale
+		lsample = sample
+		sample = (lsample + scale*(rand.Float64()*2-1)) / (1 + scale)
+		lastPos = pos
+		v := math.Min(math.Max((lsample+sample)*4/3*(1.75-scale), -1), 1)
+		return v * 0.5
+	}
+}
+
+func Phaser(pos float64) float64 {
+	// Based on https://github.com/picolove
+	pos = pos * 2
+
+	v := math.Abs(math.Mod(pos, 2)-1) - 0.5 +
+		(math.Abs(math.Mod(pos*127/128, 2)-1)-0.5)/2 - 0.25
+
+	return v * 0.7
+}

examples/audio/audio.go

@@ -11,7 +11,7 @@ func main() {
 		Notes: [32]audio.Note{
 			{
 				Pitch:      audio.PitchG3,
-				Instrument: audio.InstrumentOrgan,
+				Instrument: audio.InstrumentNoise,
 				Volume:     7,
 			},
 		},
@@ -34,7 +34,7 @@ func main() {
 			audio.SetSfx(0, sfx)
 			audio.Sfx(0, audio.Channel0, 0, 0)
 		}
-		if pi.Btnp(pi.Right) && sfx.Notes[0].Instrument < audio.InstrumentOrgan {
+		if pi.Btnp(pi.Right) && sfx.Notes[0].Instrument < audio.InstrumentPhaser {
 			sfx.Notes[0].Instrument += 1
 			audio.SetSfx(0, sfx)
 			audio.Sfx(0, audio.Channel0, 0, 0)