Fix bass channel - warmer, less synthetic sound

- Use pure triangle wave for bass preset (warmest option)
- Reduce harmonics from 64 to 16 with gentle rolloff
- Add 2kHz low-pass filter to wave channel
- Route all wave sounds through filter for warmth

src-v2/audio/apu/WaveChannel.ts

@@ -34,6 +34,7 @@ export class WaveChannel {
   private volume: WaveVolume = 1; // Default to 100%
   private outputNode: GainNode;
   private currentPreset: WavePreset;
+  private lowpassFilter: BiquadFilterNode;
   
   constructor(
     audioContext: AudioContext,
@@ -44,6 +45,14 @@ export class WaveChannel {
     this.outputNode = outputNode;
     this.currentPreset = preset;
     
+    // Create a low-pass filter to warm up the sound
+    // GB wave channel had natural rolloff from the DAC
+    this.lowpassFilter = audioContext.createBiquadFilter();
+    this.lowpassFilter.type = 'lowpass';
+    this.lowpassFilter.frequency.value = 2000; // Cut harsh highs
+    this.lowpassFilter.Q.value = 0.7;
+    this.lowpassFilter.connect(outputNode);
+    
     // Initialize wavetable with preset
     this.waveTable = new WaveTable();
     this.loadPreset(preset);
@@ -149,9 +158,9 @@ export class WaveChannel {
     const stopTime = now + duration + releaseTime;
     gain.gain.linearRampToValueAtTime(0.001, stopTime);
     
-    // Connect nodes
+    // Connect nodes through low-pass filter for warmer sound
     oscillator.connect(gain);
-    gain.connect(this.outputNode);
+    gain.connect(this.lowpassFilter);
     
     // Schedule playback
     oscillator.start(now);
@@ -211,7 +220,7 @@ export class WaveChannel {
     gain.gain.linearRampToValueAtTime(0.001, stopTime);
     
     oscillator.connect(gain);
-    gain.connect(this.outputNode);
+    gain.connect(this.lowpassFilter);
     
     oscillator.start(now);
     oscillator.stop(stopTime + 0.01);