implement linear adsr

a.csv

@@ -1,2 +1,32 @@
-0.000000,0.050625,0.151875,0.303750,0.506250,0.759375,1.063125,1.417500,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,
-0.025313,0.050625,0.101250,0.202500,0.405000,0.810000,1.620000,3.240000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,0.150000,
+x,y
+0,0.000000
+1,0.002531
+2,0.005063
+3,0.007594
+4,0.010125
+5,0.012656
+6,0.015187
+7,0.017719
+8,0.020250
+9,0.019594
+10,0.018937
+11,0.018281
+12,0.017625
+13,0.016969
+14,0.016313
+15,0.015656
+16,0.015000
+17,0.015000
+18,0.015000
+19,0.015000
+20,0.015000
+21,0.015000
+22,0.015000
+23,0.015000
+24,0.015000
+25,0.013125
+26,0.011250
+27,0.009375
+28,0.007500
+29,0.005625
+30,0.003750

b.csv

@@ -0,0 +1,33 @@
+x,y
+0,0.000000
+1,0.084375
+2,0.168750
+3,0.253125
+4,0.337500
+5,0.421875
+6,0.506250
+7,0.590625
+8,0.675000
+9,0.653125
+10,0.631250
+11,0.609375
+12,0.587500
+13,0.565625
+14,0.543750
+15,0.521875
+16,0.500000
+17,0.500000
+18,0.500000
+19,0.500000
+20,0.500000
+21,0.500000
+22,0.500000
+23,0.500000
+24,0.500000
+25,0.437500
+26,0.375000
+27,0.312500
+28,0.250000
+29,0.187500
+30,0.125000
+31,0.062500

go.mod

@@ -1,3 +1,5 @@
 module github.com/fr3fou/gusic
 
 go 1.14
+
+require github.com/davecgh/go-spew v1.1.1

go.sum

@@ -0,0 +1,2 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=

gusic/adsr.go

@@ -1,5 +1,6 @@
 package gusic
 
+// NewADSR is a constructor for an ADSR
 func NewADSR(attack, attackMultiplier, decay, decayMultiplier, sustain, release, releaseMultiplier float64) *ADSR {
 	return &ADSR{
 		attackRatio:       attack,
@@ -9,22 +10,25 @@ func NewADSR(attack, attackMultiplier, decay, decayMultiplier, sustain, release,
 		sustainRatio:      sustain,
 		releaseRatio:      release,
 		releaseMultiplier: releaseMultiplier,
+		currentMultiplier: 0.0,
 	}
 }
 
 func (a *ADSR) attack(notes []Note) {
-	multiplier := a.attackMultiplier / float64(len(notes))
+	step := a.attackMultiplier / float64(len(notes))
 
 	for i := range notes {
-		notes[i].Volume *= multiplier * float64(i)
+		notes[i].Volume *= a.currentMultiplier
+		a.currentMultiplier += step
 	}
 }
 
 func (a *ADSR) decay(notes []Note) {
-	multiplier := a.decayMultiplier / float64(len(notes))
+	step := a.decayMultiplier / float64(len(notes))
 
 	for i := range notes {
-		notes[i].Volume *= multiplier * float64(i)
+		notes[i].Volume *= a.currentMultiplier
+		a.currentMultiplier -= step
 	}
 }
 
@@ -35,13 +39,15 @@ func (a *ADSR) sustain(notes []Note) {
 }
 
 func (a *ADSR) release(notes []Note) {
-	multiplier := a.releaseMultiplier / float64(len(notes))
+	step := a.releaseMultiplier / float64(len(notes))
 
 	for i := range notes {
-		notes[i].Volume *= multiplier * float64(i)
+		notes[i].Volume *= a.currentMultiplier
+		a.currentMultiplier -= step
 	}
 }
-func (a *ADSR) apply(notes []Note) {
+
+func (a *ADSR) Apply(notes []Note) {
 	length := len(notes)
 
 	attackEnd := int(a.attackRatio * float64(length))

gusic/adsr_test.go

@@ -0,0 +1,28 @@
+package gusic
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestADSR(t *testing.T) {
+	adsr := NewADSR(0.25, 1.35, 0.25, 0.35, 0.25, 0.25, 1.0)
+
+	n := 32
+
+	notes := []Note{}
+
+	for i := 0; i < n; i++ {
+		notes = append(notes, A(4, time.Second, 0.015))
+	}
+
+	adsr.Apply(notes)
+	printVolume(notes)
+}
+
+func printVolume(notes []Note) {
+	for i, note := range notes {
+		fmt.Printf("%d,%f\n", i, note.Volume)
+	}
+}

gusic/gusic.go

@@ -30,6 +30,8 @@ type ADSR struct {
 
 	releaseRatio      float64
 	releaseMultiplier float64
+
+	currentMultiplier float64
 }
 
 // Note is a note

main_test.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestEnvelope(t *testing.T) {
+	n := 32
+
+	notes := []Sample{}
+
+	for i := 0; i < n; i++ {
+		notes = append(notes, 0.5)
+	}
+
+	printVolume(Envelope(notes, 0.25, 0.25, 0.25))
+}
+
+func printVolume(notes []Sample) {
+	for i, note := range notes {
+		fmt.Printf("%d,%f\n", i, note)
+	}
+}