Fix volume calculation

ryohey/signal#419

Author: ryohey

lib/src/processor/SynthProcessorCore.ts

@@ -95,7 +95,7 @@ export class SynthProcessorCore {
     for (const sample of samples) {
       const oscillator = new WavetableOscillator(sample, this.sampleRate)
 
-      const volume = velocity / 0x80
+      const volume = velocity / 127
       oscillator.noteOn(pitch, volume)
 
       if (state.oscillators[pitch] === undefined) {
@@ -151,12 +151,12 @@ export class SynthProcessorCore {
 
   setMainVolume(channel: number, value: number) {
     const state = this.getChannelState(channel)
-    state.volume = value / 0x80
+    state.volume = value / 127
   }
 
   expression(channel: number, value: number) {
     const state = this.getChannelState(channel)
-    state.expression = value / 0x80
+    state.expression = value / 127
   }
 
   allSoundsOff(channel: number) {
@@ -210,7 +210,7 @@ export class SynthProcessorCore {
 
   modulation(channel: number, value: number) {
     const state = this.getChannelState(channel)
-    state.modulation = value / 0x80
+    state.modulation = value / 127
   }
 
   resetChannel(channel: number) {

lib/src/processor/WavetableOscillator.ts

@@ -64,7 +64,7 @@ export class WavetableOscillator {
 
     const speed =
       (this.baseSpeed * this.speed * this.sample.sampleRate) / this.sampleRate
-    const volume = this.velocity * this.volume * this.sample.volume
+    const volume = (this.velocity * this.volume) ** 2 * this.sample.volume
 
     // zero to pi/2
     const panTheta =