From 4fe46e4cd0ef865acc144b18b3d228855cc49bf1 Mon Sep 17 00:00:00 2001
From: jbphet <jpblanco@yahoo.com>
Date: Tue, 4 Oct 2022 15:28:27 -0600
Subject: [PATCH] improve sound generation, see
 https://github.com/phetsims/greenhouse-effect/issues/185

---
 js/common/view/FluxMeterNode.ts           |  1 +
 js/common/view/FluxMeterSoundGenerator.ts | 72 +++++++++++++++--------
 2 files changed, 49 insertions(+), 24 deletions(-)

diff --git a/js/common/view/FluxMeterNode.ts b/js/common/view/FluxMeterNode.ts
index e5c3431d..b1cb2f0f 100644
--- a/js/common/view/FluxMeterNode.ts
+++ b/js/common/view/FluxMeterNode.ts
@@ -310,6 +310,7 @@ class FluxMeterNode extends Node {
   public reset(): void {
     this.wasDraggedProperty.reset();
     this.zoomFactor.reset();
+    this.soundGenerator.reset();
   }
 }
 
diff --git a/js/common/view/FluxMeterSoundGenerator.ts b/js/common/view/FluxMeterSoundGenerator.ts
index 792c3b8f..2c8e9fbe 100644
--- a/js/common/view/FluxMeterSoundGenerator.ts
+++ b/js/common/view/FluxMeterSoundGenerator.ts
@@ -17,11 +17,16 @@ import greenhouseEffect from '../../greenhouseEffect.js';
 // constants
 const DEFAULT_OUTPUT_LEVEL = 0.22;
 
-// amount of time after a change before starting the fade out, in seconds
-const PRE_FADE_TIME = 1;
+// amount of time before starting to fade where flux change is below the threshold, in seconds
+const PRE_FADE_TIME = 0.5;
 
-// amount of time to fade from full volume to zero, in seconds
-const FADE_TIME = 1;
+// rate at which the sounds increase in volume, in proportion per second
+const FADE_IN_RATE = 5;
+
+// rate at which sounds decrease in volume, in proportion per second
+const FADE_OUT_RATE = 2;
+
+const FADE_OUT_TIME = 1 / FADE_OUT_RATE;
 
 // the rate of flux change considered necessary to produce sound, empirically determined
 const FLUX_CHANGE_RATE_THRESHOLD = 300000;
@@ -60,7 +65,10 @@ class FluxMeterSoundGenerator extends SoundGenerator {
     this.irPreviousFluxUp = irFluxUpProperty.value;
 
     // Create the sound clip user for IR flux in the upward direction.
-    this.irUpFluxSoundClip = new SoundClip( irFluxUp_mp3, { rateChangesAffectPlayingSounds: false } );
+    this.irUpFluxSoundClip = new SoundClip( irFluxUp_mp3, {
+      initialOutputLevel: 0,
+      loop: true
+    } );
     this.irUpFluxSoundClip.connect( this.masterGainNode );
 
     // Define the class-specific dispose function.
@@ -78,40 +86,56 @@ class FluxMeterSoundGenerator extends SoundGenerator {
 
     const irFluxUpChangeRateThisStep = Math.abs( this.irPreviousFluxUp - this.irFluxUpProperty.value ) / dt;
 
+    // Adjust the countdown timer based on the rate of flux change.
     if ( irFluxUpChangeRateThisStep > FLUX_CHANGE_RATE_THRESHOLD ) {
-
-      // The flux is changing at a rate high enough that the corresponding sound should be produced at full volume.
-      if ( !this.irUpFluxSoundClip.isPlaying ) {
-        this.irUpFluxSoundClip.play();
-      }
-      this.irUpFluxSoundClip.outputLevel = 1;
-      this.irUpFluxChangedCountdownTimer = PRE_FADE_TIME + FADE_TIME;
+      this.irUpFluxChangedCountdownTimer = PRE_FADE_TIME + FADE_OUT_TIME;
     }
     else {
-
-      // The change during this step is below the threshold, so fade the sound.
       this.irUpFluxChangedCountdownTimer = Math.max( this.irUpFluxChangedCountdownTimer - dt, 0 );
-      if ( this.irUpFluxChangedCountdownTimer === 0 ) {
+    }
+
+    // Adjust the output level of the IR flux up sound based on the corresponding countdown timer and the current output
+    // level.
+    let irUpFluxSoundOutputLevel = this.irUpFluxSoundClip.outputLevel;
+    if ( this.irUpFluxChangedCountdownTimer > FADE_OUT_TIME ) {
 
-        // It's time to stop this sound from playing.
-        this.irUpFluxSoundClip.outputLevel = 0;
-        this.irUpFluxSoundClip.stop();
-      }
-      else if ( this.irUpFluxChangedCountdownTimer < PRE_FADE_TIME ) {
+      // Move towards full volume if not already there.
+      irUpFluxSoundOutputLevel = Math.min( irUpFluxSoundOutputLevel + FADE_IN_RATE * dt, 1 );
+    }
+    else if ( this.irUpFluxChangedCountdownTimer > 0 ) {
+      irUpFluxSoundOutputLevel = Math.max( irUpFluxSoundOutputLevel - FADE_OUT_RATE * dt, 0 );
+    }
+    else {
+      irUpFluxSoundOutputLevel = Math.max( irUpFluxSoundOutputLevel - 0.1 * dt, 0 );
+    }
 
-        // Based on the countdown timer value, this sound is fading, so set the output level appropriately.
-        this.irUpFluxSoundClip.outputLevel = Math.max( this.irUpFluxChangedCountdownTimer - PRE_FADE_TIME / FADE_TIME, 0 );
-      }
+    // Start or stop the sound clip if appropriate.
+    if ( irUpFluxSoundOutputLevel > 0 && !this.irUpFluxSoundClip.isPlaying ) {
+      this.irUpFluxSoundClip.play();
+    }
+    else if ( irUpFluxSoundOutputLevel === 0 && this.irUpFluxSoundClip.isPlaying ) {
+      this.irUpFluxSoundClip.stop( 0.1 );
     }
 
+    // Set the output level.
+    this.irUpFluxSoundClip.setOutputLevel( irUpFluxSoundOutputLevel );
+
     // Set the playback rate for the IR up sound.  This happens regardless of whether it is playing.
-    const playbackRate = 1 + Math.min( this.irFluxUpProperty.value / MAX_EXPECTED_IR_FLUX, 1 ) * 2;
+    const playbackRate = 1 + Math.min( this.irFluxUpProperty.value / MAX_EXPECTED_IR_FLUX, 1 ) * 4;
     this.irUpFluxSoundClip.setPlaybackRate( playbackRate );
 
     // Update the previous flux values for the next step.
     this.irPreviousFluxUp = this.irFluxUpProperty.value;
   }
 
+  public reset(): void {
+    this.irUpFluxChangedCountdownTimer = 0;
+    this.irUpFluxSoundClip.outputLevel = 0;
+    this.irUpFluxSoundClip.stop( 0.1 );
+    this.irUpFluxSoundClip.setPlaybackRate( 1 );
+    this.irPreviousFluxUp = 0;
+  }
+
   public override dispose(): void {
     this.disposeFluxMeterSoundGenerator();
     super.dispose();