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Andre Zeps 8579145c66 AD7528: Reduces volume of input to 56%

- Approximates the clipping behavior of a CDI 210/05
- Required to fit the theoretical 17 bit output
  into the 16 bit PCM signal of the MiSTer
- Fixes sound distortion in Hotel Mario

2025-03-28 19:27:09 +01:00

3.7 KiB

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Audio Mixer

for both AD7528, the input A is the same side while the input B is the other side
- 7530 AD7528 produces Audio Right
  - VrefA is DAC Right
  - VrefB is DAC Left
- 7550 AD7528 produces Audio Left
  - VrefA is DAC Left
  - VrefB is DAC Right

Muting results into all DAC values being 0

Audio CD

The system settings have 5 volume levels

Level 0

factor_left_a   0x00
factor_left_b   0x40
factor_right_a  0x00
factor_right_b  0x40

Level 1

factor_left_a   0x00
factor_left_b   0x5B
factor_right_a  0x00
factor_right_b  0x5B

Level 3

factor_left_a   0x00
factor_left_b   0x80
factor_right_a  0x00
factor_right_b  0x80

Level 4

factor_left_a   0x00
factor_left_b   0xB5
factor_right_a  0x00
factor_right_b  0xB5

Level 5

factor_left_a   0x00
factor_left_b   0xFF
factor_right_a  0x00
factor_right_b  0xFF

Note: For some reason, these settings are not transported using the Cx command

Zelda - Wand of Gamelon

Philips Logo (Stereo Music)

Atten: ca  7f 0 7f 0
DAC Left 0   0
DAC Left 1 255
DAC Right 0   0
DAC Right 1 255

Intro Logo

Atten: c0  0 0 0 0
DAC Right 0 255
DAC Left 1 255
DAC Left 0 255
DAC Right 1 255

King Opening Cutscene

Atten: c0  0 0 0 0
DAC Right 0 255
DAC Left 1 255
DAC Left 0 255
DAC Right 1 255

Map (Stereo Music)

Atten: ca  7f 0 7f 0
DAC Left 0   0
DAC Left 1 255
DAC Right 0   0
DAC Right 1 255

Ingame (2 Mono mixed in one)

Atten: c0  0 0 0 0
DAC Right 0 255
DAC Left 1 255
DAC Left 0 255
DAC Right 1 255

Ingame (2 Mono but both damped)

Atten: c0  c c c c
DAC Right 0  64
DAC Left 1  64
DAC Left 0  64
DAC Right 1  64

Zelda's Adventure

Philips Logo + Intro Cutscene

Atten: c5  0 0 0 0
DAC Left 0 255
DAC Left 1   0
DAC Right 0 255
DAC Right 1   0

BGM is on the left channel. SFX is on the right channel.

Atten: c0  0 0  0 12   Zelda at right edge

DAC Left 0 255
DAC Left 1 255
DAC Right 0 255
DAC Right 1  64

Atten: c0  0 0 12  0   Zelda at left edge

DAC Left 0  64
DAC Left 1 255
DAC Right 0 255
DAC Right 1 255

Atten: c0  0 0  0  0   Zelda in center

DAC Left 1 255
DAC Left 0 255
DAC Right 0 255
DAC Right 1 255

Hotel Mario

Philips Logo, Intro, Menu and ingame

Atten: c0  0 0 0 0

factor_left_a   0xFF
factor_left_b   0xFF
factor_right_a  0xFF
factor_right_b  0xFF

Experiments with SDK API

According to the green book, the bit 7 mutes the Audio. Let's test that. Both of these cause a factor of 00 on mixer.

sc_atten(Sound, 0xe0e0e0e0);

Unmute 83
Atten: cf  60 60 60 60
Atten: cf  60 60 60 60
Mute   82

or this

sc_atten(Sound, 0x80808080);

Unmute 83
Atten: cf  0 0 0 0
Atten: cf  0 0 0 0
Mute   82

This here is used by Frog Feast. All A factors are 0xff while B factors are 00 causing a full stereo signal.

/* Set maximum volume in left-left and right-right channels */
sc_atten(Sound, 0x00800080);

Unmute 83
Atten: c5  0 0 0 0
Atten: c5  0 0 0 0
Mute   82

This here does factor 0xff on all 4 parameters. It transforms stereo into mono:

sc_atten(Sound, 0x0);

Unmute 83
Atten: c0  0 0 0 0
Atten: c0  0 0 0 0
Mute   82

It can't hear it but this should swap the channels:

sc_atten(Sound, 0x80008000);

Unmute 83
Atten: ca  0 0 0 0
Atten: ca  0 0 0 0
Mute   82

At least this is what I assume, considering that all A factors are 00 while all B factors are 0xff.

This also means that there is a translation layer in the software.

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