add dipped crossfade type

src/components/player/Player.tsx

@@ -80,6 +80,14 @@ const listenHandler = (
             nextPlayerVolumeCalculation =
               ((fadeDuration - timeLeft) / fadeDuration) * playQueue.volume;
             break;
+          case 'dipped':
+            // https://math.stackexchange.com/a/4622
+            percentageOfFadeLeft = timeLeft / fadeDuration;
+            currentPlayerVolumeCalculation =
+              (percentageOfFadeLeft * playQueue.volume) ** 2;
+            nextPlayerVolumeCalculation =
+              ((percentageOfFadeLeft - 1) * playQueue.volume) ** 2;
+            break;
           default:
             currentPlayerVolumeCalculation =
               (timeLeft / fadeDuration) * playQueue.volume;

src/components/settings/Config.tsx

@@ -232,6 +232,7 @@ const Config = () => {
           >
             <Radio value="equalPower">Equal Power</Radio>
             <Radio value="linear">Linear</Radio>
+            <Radio value="dipped">Dipped</Radio>
           </RadioGroup>
           <br />
           <ControlLabel>Volume fade</ControlLabel>