Create audio from raw bits in Scala

music.scala

package com.awwsmm

import javax.sound.sampled.{AudioFormat, AudioSystem, SourceDataLine}

// Inspired by https://community.oracle.com/tech/developers/discussion/1273219/example-code-to-generate-audio-tone
// and https://stackoverflow.com/questions/1932490/java-generating-sound/47916383

// still some "crackling" / "popping" at the end of the tune, but most of the way there
object Main extends App {

  val G  = 196.00 // Hz
  val Eb = 155.56
  val F  = 174.61
  val D  = 146.83

  val bpm = 108.0
  val quarter = 1000.0 * 60.0 / bpm
  val triplet = quarter / 3.0
  val half = quarter * 2.0

  val quarterRest = Note(0, quarter, 0)
  val tripletG = Note(G, triplet)
  val halfEb = Note(Eb, half)
  val tripletF = Note(F, triplet)
  val halfD = Note(D, half)

  val bars12: List[Note] = List(quarterRest, tripletG, tripletG, tripletG, halfEb)
  val bars34: List[Note] = List(quarterRest, tripletF, tripletF, tripletF, halfD, quarterRest)

  val tune = Tune.empty

  (bars12 ++ bars34).foreach(tune.addNote)

  tune.play()
  tune.close()
}

object Tune {
  def empty: Tune = {
    val sampleRate = 44100 // samples / sec
    val audioFormat = new AudioFormat(sampleRate, 8, 1, true, false)
    new Tune(sampleRate, audioFormat)
  }
}

class Tune(val sampleRate: Int, audioFormat: AudioFormat) {

  private[this] var sourceDataLine: Option[SourceDataLine] = None
  private[this] var ready = false

  private var bytes = Array[Byte]()

  def start(): Unit = {
    sourceDataLine = Some(AudioSystem.getSourceDataLine(audioFormat))
    sourceDataLine.get.open(audioFormat)
    sourceDataLine.get.flush() // this eliminates "crackling" / "popping" at the beginning of the tune
    sourceDataLine.get.start()
    ready = true
  }

  def addNote(note: Note): Unit = {
    bytes ++= note.bytes(sampleRate)
  }

  def play(): Unit = {
    if (!ready) start()
    sourceDataLine.get.write(bytes, 0, bytes.length)
    sourceDataLine.get.drain() // this causes the "crackling" / "popping" at the end of the tune
  }

  def close(): Unit = {
    sourceDataLine.foreach(_.flush())
    sourceDataLine.foreach(_.stop())
    sourceDataLine.foreach(_.close())
    ready = false
  }
}

case class Note(frequency: Double, msecs: Double, volume: Double = 128.0, fade: Boolean = true) {

  // this (mostly) eliminates "crackling" / "popping" at the beginning / end of each tone
  def fadeVolume(sampleIndex: Int, nSamples: Int): Double = {
    val fadedSamples = 0.1 * nSamples // 10% fade in/out

    if (sampleIndex < fadedSamples) { // fade in
      val x = sampleIndex / fadedSamples // [0, 1]
      x * x * volume
    } else if ((nSamples - sampleIndex) < fadedSamples) { // fade out
      val x = (nSamples - sampleIndex) / fadedSamples // [0, 1]
      x * x * volume
    } else volume
  }

  val wavelength: Double = 2.0 * Math.PI * frequency

  def bytes(sampleRate: Int): Array[Byte] = {
    val nSamples = (msecs * sampleRate / 1000.0).toInt
    (0 to nSamples).map({ sampleIndex =>
      val angle = wavelength * sampleIndex / sampleRate
      val fadedVolume = if (fade) fadeVolume(sampleIndex, nSamples) else volume
      (Math.sin(angle) * fadedVolume).toByte
    }).toArray
  }
}

// notes
// https://stackoverflow.com/questions/9630324/popping-crackling-when-using-a-java-source-data-line-for-audio
// https://stackoverflow.com/questions/34579950/java-audio-crackling
// https://community.oracle.com/tech/developers/discussion/1273219/example-code-to-generate-audio-tone
// https://stackoverflow.com/questions/59888683/consistent-popping-sound-while-playing-audio-through-a-sourcedataline
// https://stackoverflow.com/questions/57207927/preventing-the-click-when-stopping-sourcedataline