draft a simpler version of the bell eq

patch.go

@@ -206,6 +206,11 @@ var UnitTypes = map[string]([]UnitParameter){
 		{Name: "stereo", MinValue: 0, MaxValue: 1, CanSet: true, CanModulate: false},
 		{Name: "channel", MinValue: 0, MaxValue: 6, CanSet: true, CanModulate: false, DisplayFunc: arrDispFunc(channelNames[:])}},
 	"sync": []UnitParameter{},
+	"eq": []UnitParameter{
+		{Name: "stereo", MinValue: 0, MaxValue: 1, CanSet: true, CanModulate: false},
+		{Name: "frequency", MinValue: 0, MaxValue: 128, CanSet: true, CanModulate: true, DisplayFunc: func(v int) (string, string) { return filterFrequencyDispFunc(v) }},
+		{Name: "bandwidth", MinValue: 0, MaxValue: 128, CanSet: true, CanModulate: true, DisplayFunc: func(v int) (string, string) { return eqBWdisplayFunc(v) }},
+		{Name: "gain", MinValue: 0, Neutral: 64, MaxValue: 128, CanSet: true, CanModulate: true, DisplayFunc: func(v int) (string, string) { return eqGainDisplayFunc(v) }}},
 }
 
 // compile errors if interface is not implemented.
@@ -266,6 +271,13 @@ func filterFrequencyDispFunc(v int) (string, string) {
 	return strconv.FormatFloat(f, 'f', 0, 64), "Hz"
 }
 
+func eqBWdisplayFunc(v int) (string, string) {
+	return strconv.FormatFloat(float64(v)/64.*100, 'f', 2, 64), "%"
+}
+func eqGainDisplayFunc(v int) (string, string) {
+
+	return strconv.FormatFloat(40*(float64(v)/64.-1.), 'f', 2, 64), "dB"
+}
 func compressorTimeDispFunc(v int) (string, string) {
 	alpha := math.Pow(2, -24*float64(v)/128) // alpha is the "smoothing factor" of first order low pass iir
 	sec := -1 / (44100 * math.Log(1-alpha))  // from smoothing factor to time constant, https://en.wikipedia.org/wiki/Exponential_smoothing
@@ -435,6 +447,7 @@ var stackUseMonoStereo = map[string][2]StackUse{
 		{Inputs: [][]int{{0}}, Modifies: []bool{false}, NumOutputs: 1},
 		{},
 	},
+	"eq": stackUseEffect,
 }
 var stackUseSendNoPop = [2]StackUse{
 	{Inputs: [][]int{{0}}, Modifies: []bool{true}, NumOutputs: 1},

tracker/presets.go

@@ -464,6 +464,7 @@ var defaultUnits = map[string]sointu.Unit{
 	"compressor": {Type: "compressor", Parameters: map[string]int{"stereo": 0, "attack": 64, "release": 64, "invgain": 64, "threshold": 64, "ratio": 64}},
 	"send":       {Type: "send", Parameters: map[string]int{"stereo": 0, "amount": 64, "voice": 0, "unit": 0, "port": 0, "sendpop": 1}},
 	"sync":       {Type: "sync", Parameters: map[string]int{}},
+	"eq":         {Type: "eq", Parameters: map[string]int{"stereo": 0, "frequency": 64, "bandwidth": 64, "gain": 64}},
 }
 
 var defaultInstrument = sointu.Instrument{

vm/go_synth.go

@@ -594,6 +594,23 @@ func (s *GoSynth) Render(buffer sointu.AudioBuffer, maxtime int) (samples int, r
 				if stereo {
 					stack = append(stack, gain)
 				}
+			case opEq:
+				for i := range channels {
+					inputSample := stack[l-1-i]
+					w := params[0] * params[0]
+					alpha := w * params[1] * 2
+					A := float32(math.Pow(2, float64(params[2]-.5)*6.643856189774724))
+					u := alpha * A
+					v := alpha / A
+
+					a0, a1, a2 := 1+v, w*w-2, 1-v
+					b0, b1, b2 := 1+u, a1, 1-u
+
+					output := (b0*inputSample + unit.state[i]) / a0
+					unit.state[i] = b1*inputSample - b1*output + unit.state[2+i]
+					unit.state[2+i] = b2*inputSample - a2*output
+					stack[l-1-i] = output
+				}
 			case opSync:
 				break
 			default:

vm/go_synth_test.go

@@ -109,6 +109,7 @@ var defaultUnits = map[string]sointu.Unit{
 	"compressor": {Type: "compressor", Parameters: map[string]int{"stereo": 0, "attack": 64, "release": 64, "invgain": 64, "threshold": 64, "ratio": 64}},
 	"send":       {Type: "send", Parameters: map[string]int{"stereo": 0, "amount": 128, "voice": 0, "unit": 0, "port": 0, "sendpop": 1}},
 	"sync":       {Type: "sync", Parameters: map[string]int{}},
+	"eq":         {Type: "eq", Parameters: map[string]int{"stereo": 0, "freq": 1000, "q": 10, "gain": 64}},
 }
 
 var defaultInstrument = sointu.Instrument{

vm/opcodes.go

@@ -12,27 +12,28 @@ const (
 	opDelay      = 8
 	opDistort    = 9
 	opEnvelope   = 10
-	opFilter     = 11
-	opGain       = 12
-	opHold       = 13
-	opIn         = 14
-	opInvgain    = 15
-	opLoadnote   = 16
-	opLoadval    = 17
-	opMul        = 18
-	opMulp       = 19
-	opNoise      = 20
-	opOscillator = 21
-	opOut        = 22
-	opOutaux     = 23
-	opPan        = 24
-	opPop        = 25
-	opPush       = 26
-	opReceive    = 27
-	opSend       = 28
-	opSpeed      = 29
-	opSync       = 30
-	opXch        = 31
+	opEq         = 11
+	opFilter     = 12
+	opGain       = 13
+	opHold       = 14
+	opIn         = 15
+	opInvgain    = 16
+	opLoadnote   = 17
+	opLoadval    = 18
+	opMul        = 19
+	opMulp       = 20
+	opNoise      = 21
+	opOscillator = 22
+	opOut        = 23
+	opOutaux     = 24
+	opPan        = 25
+	opPop        = 26
+	opPush       = 27
+	opReceive    = 28
+	opSend       = 29
+	opSpeed      = 30
+	opSync       = 31
+	opXch        = 32
 )
 
-var transformCounts = [...]int{0, 0, 1, 0, 5, 1, 1, 4, 1, 5, 2, 1, 1, 0, 1, 0, 1, 0, 0, 2, 6, 1, 2, 1, 0, 0, 0, 1, 0, 0, 0}
+var transformCounts = [...]int{0, 0, 1, 0, 5, 1, 1, 4, 1, 5, 3, 2, 1, 1, 0, 1, 0, 1, 0, 0, 2, 6, 1, 2, 1, 0, 0, 0, 1, 0, 0, 0}