proper DMA/PSG balance, use soundbias, remove offset for silence

src/crab/apu.cr

@@ -20,7 +20,7 @@ class APU
   @soundcnt_l = Reg::SOUNDCNT_L.new 0
   getter soundcnt_h = Reg::SOUNDCNT_H.new 0
   @sound_enabled : Bool = false
-  @soundbias = Reg::SOUNDBIAS.new 0
+  @soundbias = Reg::SOUNDBIAS.new 0x3FE
 
   @buffer = Slice(Int16).new BUFFER_SIZE
   @buffer_pos = 0
@@ -101,29 +101,25 @@ class APU
 
   def get_sample : Nil
     abort "Prohibited sound 1-4 volume #{@soundcnt_h.sound_volume}" if @soundcnt_h.sound_volume >= 3
-    # Puts PSGs on scale of 0...0x40
+    # Gets PSGs on scale of -0x80..0x80 each
     psg_sound = ((@channel1.get_amplitude * @soundcnt_l.channel_1_left) +
                  (@channel2.get_amplitude * @soundcnt_l.channel_2_left) +
                  (@channel3.get_amplitude * @soundcnt_l.channel_3_left) +
-                 (@channel4.get_amplitude * @soundcnt_l.channel_4_left))# * 2 - 0x80
-    # Puts PSGs on scale of 0...0x200
-    psg_left = (psg_sound * @soundcnt_l.left_volume) >> (2 - @soundcnt_h.sound_volume)
-    psg_right = (psg_sound * @soundcnt_l.right_volume) >> (2 - @soundcnt_h.sound_volume)
+                 (@channel4.get_amplitude * @soundcnt_l.channel_4_left))
+    # Keep PSGs on scale of -0x200...0x200 (shift by `5 - vol` to account for `*8` from left/right vol)
+    psg_left = (psg_sound * @soundcnt_l.left_volume) >> (5 - @soundcnt_h.sound_volume)
+    psg_right = (psg_sound * @soundcnt_l.right_volume) >> (5 - @soundcnt_h.sound_volume)
 
     # Gets DMAs on scale of -0x100...0x100
     dma_a, dma_b = @dma_channels.get_amplitude
-    dma_a <<= 1
-    dma_b <<= 1
     # Puts DMAs on scale of -0x200...0x200
     dma_a <<= @soundcnt_h.dma_sound_a_volume
     dma_b <<= @soundcnt_h.dma_sound_b_volume
     dma_left = dma_a * @soundcnt_h.dma_sound_a_left + dma_b * @soundcnt_h.dma_sound_b_left
     dma_right = dma_a * @soundcnt_h.dma_sound_a_right + dma_b * @soundcnt_h.dma_sound_b_right
 
-    bias = 0x200
-
-    total_left = (psg_left + dma_left + bias).clamp(0_i16..0x3FF_i16)
-    total_right = (psg_right + dma_right + bias).clamp(0_i16..0x3FF_i16)
+    total_left = (psg_left + dma_left + @soundbias.bias_level).clamp(0_i16..0x3FF_i16) - @soundbias.bias_level
+    total_right = (psg_right + dma_right + @soundbias.bias_level).clamp(0_i16..0x3FF_i16) - @soundbias.bias_level
 
     @buffer[@buffer_pos] = total_left * 32
     @buffer[@buffer_pos + 1] = total_right * 32

src/crab/apu/channel1.cr

@@ -1,9 +1,9 @@
 class Channel1 < VolumeEnvelopeChannel
   WAVE_DUTY = [
-    [0, 0, 0, 0, 0, 0, 0, 1], # 12.5%
-    [1, 0, 0, 0, 0, 0, 0, 1], # 25%
-    [1, 0, 0, 0, 0, 1, 1, 1], # 50%
-    [0, 1, 1, 1, 1, 1, 1, 0], # 75%
+    [-8, -8, -8, -8, -8, -8, -8, +8], # 12.5%
+    [+8, -8, -8, -8, -8, -8, -8, +8], # 25%
+    [+8, -8, -8, -8, -8, +8, +8, +8], # 50%
+    [-8, +8, +8, +8, +8, +8, +8, -8], # 75%
   ]
 
   RANGE = 0x60..0x67
@@ -57,7 +57,7 @@ class Channel1 < VolumeEnvelopeChannel
     end
   end
 
-  # Outputs a value 0..0xF
+  # Outputs a value -0x80..0x80
   def get_amplitude : Int16
     if @enabled && @dac_enabled
       WAVE_DUTY[@duty][@wave_duty_position].to_i16 * @current_volume

src/crab/apu/channel2.cr

@@ -1,9 +1,9 @@
 class Channel2 < VolumeEnvelopeChannel
   WAVE_DUTY = [
-    [0, 0, 0, 0, 0, 0, 0, 1], # 12.5%
-    [1, 0, 0, 0, 0, 0, 0, 1], # 25%
-    [1, 0, 0, 0, 0, 1, 1, 1], # 50%
-    [0, 1, 1, 1, 1, 1, 1, 0], # 75%
+    [-8, -8, -8, -8, -8, -8, -8, +8], # 12.5%
+    [+8, -8, -8, -8, -8, -8, -8, +8], # 25%
+    [+8, -8, -8, -8, -8, +8, +8, +8], # 50%
+    [-8, +8, +8, +8, +8, +8, +8, -8], # 75%
   ]
 
   RANGE = 0x68..0x6F
@@ -33,7 +33,7 @@ class Channel2 < VolumeEnvelopeChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel2
   end
 
-  # Outputs a value 0..0xF
+  # Outputs a value -0x80..0x80
   def get_amplitude : Int16
     if @enabled && @dac_enabled
       WAVE_DUTY[@duty][@wave_duty_position].to_i16 * @current_volume

src/crab/apu/channel3.cr

@@ -8,7 +8,7 @@ class Channel3 < SoundChannel
 
   @wave_ram = Array(Bytes).new 2, Bytes.new(WAVE_RAM_RANGE.size) { |idx| idx & 1 == 0 ? 0x00_u8 : 0xFF_u8 }
   @wave_ram_position : UInt8 = 0
-  @wave_ram_sample_buffer : Int16 = 0x00
+  @wave_ram_sample_buffer : UInt8 = 0x00
 
   # NR30
   @wave_ram_dimension : Bool = false
@@ -27,7 +27,8 @@ class Channel3 < SoundChannel
   def step_wave_generation : Nil
     @wave_ram_position = (@wave_ram_position + 1) % (WAVE_RAM_RANGE.size * 2)
     @wave_ram_bank ^= 1 if @wave_ram_position == 0 && @wave_ram_dimension
-    @wave_ram_sample_buffer = @wave_ram[@wave_ram_bank][@wave_ram_position // 2].to_i16
+    full_sample = @wave_ram[@wave_ram_bank][@wave_ram_position // 2]
+    @wave_ram_sample_buffer = (full_sample >> (@wave_ram_position & 1 == 0 ? 4 : 0)) & 0xF
   end
 
   def frequency_timer : UInt32
@@ -38,11 +39,10 @@ class Channel3 < SoundChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel3
   end
 
-  # Outputs a value 0..0xF
+  # Outputs a value -0x80..0x80
   def get_amplitude : Int16
     if @enabled && @dac_enabled
-      volume_shift = (-1 + @volume_code) % 4
-      (((@wave_ram_sample_buffer >> (@wave_ram_position & 1 == 0 ? 4 : 0)) & 0x0F) >> volume_shift)
+      (@wave_ram_sample_buffer.to_i16 - 8) * 4 * (@volume_force ? 3 : {0, 4, 2, 1}[@volume_code])
     else
       0_i16
     end

src/crab/apu/channel4.cr

@@ -33,10 +33,10 @@ class Channel4 < VolumeEnvelopeChannel
     @gba.scheduler.schedule frequency_timer, ->step, Scheduler::EventType::APUChannel4
   end
 
-  # Outputs a value 0..0xF
+  # Outputs a value -0x80..0x80
   def get_amplitude : Int16
     if @enabled && @dac_enabled
-      ((~@lfsr & 1) * @current_volume).to_i16
+      ((~@lfsr & 1).to_i16 * 16 - 8) * @current_volume
     else
       0_i16
     end

src/crab/apu/dma_channels.cr

@@ -37,7 +37,7 @@ class DMAChannels
       if timer == @timers[channel].call
         if @sizes[channel] > 0
           log "Timer overflow good; channel:#{channel}, timer:#{timer}".colorize.fore(:yellow)
-          @latches[channel] = @fifos[channel][@positions[channel]].to_i16
+          @latches[channel] = @fifos[channel][@positions[channel]].to_i16 << 1 # put on scale of -0x100..0x100
           @positions[channel] = (@positions[channel] + 1) % 32
           @sizes[channel] -= 1
         else