Sound

The WonderSwan features the following sound hardware:

• Four audio channels:
  • channel 1 - wavetable (32 x 4-bit samples),
  • channel 2 - wavetable or 8-bit unsigned PCM sample,
  • channel 3 - wavetable with optional hardware sweep,
  • channel 4 - wavetable or LFSR noise,
• Hyper Voice^(color) - headphone output exclusive 16-bit stereo PCM output,
• 24000 Hz output:
  • internal speaker - 8-bit, mono,
  • headphone output - 16-bit, stereo.

The sound is mixed as follows:

      Ch1 Ch2 Ch3 Ch4                        Glossary: L = left, R = right, M = mono 
       |   |   |   |                                               Mnn = nn-bit mono
       8   8   8   8      port $98                            port $nn =  value port
       |   |   |   |       /
      _V___V___V___V_     /              _____          _____
     |               |--L10------+------|     |        |     |
     |       +       |           |      |  +  |--M11-->| >>r |--M8--> Speaker output
     |_______________|--R10------|-+----|_____|  /     |_____|
                        /       _|_|_           /     (r=0...3)
                       /       |     |         /
                  port $96     | <<5 |      port $9A
                               |_____|
                                 | |
                                 | |
port $68            port $64     | |
 /    _______________   \      __V_V__                  _____
L8-->| (Color only)  |--L16-->|       |----------L16---|     |
     |  Hyper Voice  |        |  + +  |                | I2S |------> Headphone output
R8-->|_______________|--R16-->|_______|----------R16---|_____|
 \                      /
port $69            port $66

Hyper Voice functionality is documented on its own sub-page.

I/O Ports

Sound Channel Frequency

15  bit  8  7  bit  0
 ---------  ---------
 .... .ddd  dddd dddd
       +++--++++-++++- Frequency divisor

This frequency is used for wavetable output. It is calculated as follows: sample rate = 3072000 Hz / (2048 - divisor).

Note that this refers to the sample rate of the wavetable, and needs to be scaled accordingly for a given waveform when performing music playback.

Sound Channel Volume

7  bit  0
---------
llll rrrr
|||| ++++- Right channel volume (0-15)
++++------ Left channel volume (0-15)

This volume is used for wavetable output.

The calculation to get an unsigned 8-bit sample out of a 4-bit wavetable sample / 4-bit volume pair is simple: out_sample = sample * volume. This means that the maximum sample in wavetable output mode is 15 * 15 = 225.

Sound Channel 2 Voice Sample

7  bit  0
---------
ssss ssss
++++-++++- Unsigned 8-bit PCM sample (0-255)

This sample is used for voice output.

Sound Channel 3 Sweep Amount

7  bit  0
---------
vvvv vvvv
++++-++++- Value; 8-bit, signed.

This port is used for wavetable output with sweep enabled.

The signed value in this port will be added to the frequency divider for channel 3 every sweep step (as determined by the Sweep Ticks port). Wraparound is present - adding 1 to a frequency divider value of 2047 will cause it to roll over back to 0.

Sound Channel 3 Sweep Ticks

7  bit  0
---------
...t tttt
   +-++++- Ticks per step - 1

This port is used for wavetable output with sweep enabled.

Every ttttt + 1 ticks, clocked at 375 Hz, the value in the Sweep Amount port will be added to the frequency divider for channel 3.

Sound Channel 4 Noise Control

7  bit  0
---- ----
...e rttt
   | |+++- LFSR tap mode
   | +---- LFSR reset: 1 = reset shift register
   +------ LFSR enabled: 0 = off, 1 = on

This port is used for noise output.

List of LFSR tap modes

Tap mode	Tap bit	Sequence length
0	14	32767
1	10	1953
2	13	254
3	4	217
4	8	73
5	6	63
6	9	42
7	11	28

Noise output works using the following algorithm, performed once per sample generated:

1. Create a new bit by XORing bit 7 with the tap bit.
2. Shift the LFSR register one bit to the left.
3. Write the new bit as bit 0.
4. Use the new bit as if it were a wavetable sample: 0 = 0, 1 = 15.

Sound Wavetable Address

7  bit  0
---- ----
wwww wwww
++++-++++- Wavetable address (bits 6-13)

Sound Channel Control

7  bit  0
---- ----
nsv. 4321
|||  |||+- Channel 1 enable
|||  ||+-- Channel 2 enable
|||  |+--- Channel 3 enable
|||  +---- Channel 4 enable
||+------- Channel 2 mode: 0 = wavetable, 1 = voice
|+-------- Channel 3 sweep: 0 = disable, 1 = enable
+--------- Channel 4 mode: 0 = wavetable, 1 = noise

Sound Output Control

7  bit  0
---- ----
H... hrrs
|    |||+- Internal speaker output enable
|    |++-- Internal speaker shift right value
|    +---- Headphone output enable
+--------- Headphones connected: 1 if true

It is a good idea to set the internal speaker shift right value correctly. If the value is too low, multi-channel music will clip; if the value is too high, single-channel PCM sample playback will be very quiet.

Sound Channel 4 LFSR Register

15  bit  8  7  bit  0
 ---- ----  ---- ----
 .rrr rrrr  rrrr rrrr
  +++-++++--++++-++++- Shift register value

Sound Channel 2 Voice Volume

7  bit  0
---- ----
.... lLrR
     |||+- Right channel 100% volume
     ||+-- Right channel 50% volume
     |+--- Left channel 100% volume
     +---- Left channel 50% volume

This port is used for voice output.

The 50% volume have no effect if their respective 100% volume bits are set.