From d4873545b2c22d3822453023b66172099d0f5a39 Mon Sep 17 00:00:00 2001
From: Steven Hugg <hugg@fasterlight.com>
Date: Sat, 24 Aug 2019 10:46:32 -0400
Subject: [PATCH] audio: remove dc bias

---
 src/audio.ts           | 7 ++++---
 src/machine/vicdual.ts | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/audio.ts b/src/audio.ts
index 9a48b2df..75eacf84 100644
--- a/src/audio.ts
+++ b/src/audio.ts
@@ -395,10 +395,11 @@ export var SampleAudio = function(clockfreq) {
     self.sr=self.context.sampleRate;
     self.bufferlen=2048;
 
-    // Amiga 500 fixed filter at 6kHz. WebAudio lowpass is 12dB/oct, whereas
-    // older Amigas had a 6dB/oct filter at 4900Hz.
+    // remove DC bias
     self.filterNode=self.context.createBiquadFilter();
-    self.filterNode.frequency.value=6000;
+    self.filterNode.type='lowshelf';
+    self.filterNode.frequency.value=100;
+    self.filterNode.gain.value=-6;
 
     // mixer
     if ( typeof self.context.createScriptProcessor === 'function') {
diff --git a/src/machine/vicdual.ts b/src/machine/vicdual.ts
index 184860a0..391ab0da 100644
--- a/src/machine/vicdual.ts
+++ b/src/machine/vicdual.ts
@@ -27,7 +27,7 @@ const vsyncFrequency = hsyncFrequency / 0x148;
 const cpuCyclesPerLine = cpuFrequency / hsyncFrequency;
 const timerFrequency = 500; // input 2 bit 0x8
 const cyclesPerTimerTick = cpuFrequency / (2 * timerFrequency);
-const audioOversample = 4;
+const audioOversample = 2;
 const audioSampleRate = 60 * scanlinesPerFrame; // why not hsync?
 
 export class VicDual extends BasicScanlineMachine {