Signal Generator

sigen.go

package main

import (
	"math"
	"os/exec"
)

const (
	tau float64 = math.Pi * 2
)

type Sin struct {
	Vol float64
	Freq float64
}

func (s *Sin) DSP(t float64) float64 {
	return math.Sin(tau * s.Freq * t) * s.Vol
}

type Square struct {
	Vol float64
	Freq float64
}

func (s *Square) DSP(t float64) float64 {
	if math.Sin(tau * s.Freq * t) > 0 {
		return 1 * s.Vol
	}
	return -1 * s.Vol
}


type SigGen interface {
	DSP(float64) float64
}

type DDC struct {
	Frame uint64
	Rate int32
	In SigGen
}

func (d *DDC) Read(p []byte) (n int, err error) {
	for n=0; n < len(p); n++ {
		var b float64 = (d.In.DSP(float64(d.Frame) / float64(d.Rate))/2+0.5) * 0xff
		if b > 0xff {
			b = 0xff
		}else if b < 0x00 {
			b = 0x00
		}
		p[n] = byte(b)
		d.Frame++
	}
	return
}

type Mixer struct {
	Ins []SigGen
}

func (m *Mixer) DSP(t float64) float64 {
	var mix float64 = 0
	for n := 0; n < len(m.Ins); n++ {
		mix += m.Ins[n].DSP(t)
	}
	return mix
}

func main() {

	sin := new(Sin)
	sin.Freq = 438
	sin.Vol = 0.2

	sqr := new(Square)
	sqr.Freq = 440
	sqr.Vol = 0.2

	mxr := new(Mixer)
	mxr.Ins = make([]SigGen, 2)
	mxr.Ins[0] = sin
	mxr.Ins[1] = sqr
	
	ddc := new(DDC)
	ddc.Rate = 44100
	ddc.In = mxr

	cmd := exec.Command("pacat", "--format=u8", "--channels=1")
	cmd.Stdin = ddc
	cmd.Run()
 
}