u/RSS130871

Continuing the PSG sound-design deep-dive for Cloaca Maxima.

Last time I focused on Register 13 (“Volume over Time”), which controls how sounds fade, pulse and evolve.

This time I dug into Registers 0..5: the actual TONE generators.
What started as a simple question (“how does the PSG represent musical notes internally?”) quickly turned into a fascinating little hardware archaeology project.

The key realization is that the MSX PSG does NOT store frequencies directly. Instead, it stores timer divisions called “periods”, split across two registers (“fine” and “coarse”) to form a 12-bit value.

So the process becomes:

NOTE → FREQUENCY → PERIOD → REGISTER VALUES

The attached charts show:

• the frequencies of musical notes,
• how these translate into PSG periods,
• and finally how those periods are split into actual SOUND register values.

I'm curious, is this kind of post interesting...?
Let me know!

Greetings, Ron.

P.S.: I hope this answers your question, u/riotinareasouthwest

I'm currently working on the SOUNDSCAPE for Cloaca Maxima.

First things first: there will NOT be in-game music.

Partly because of memory limitations on a stock MSX1, but mostly because it simply wouldn’t fit the atmosphere. There’s no marching band accompanying four terrified Romans into the ancient sewers beneath Rome.

What will be present are sound effects:

• dripping water,
• distant gusts of wind,
• metallic grates,
• footsteps,

To achieve this, I’ve started diving deep into the MSX PSG (Programmable Sound Generator), and honestly: the existing documentation is REALLY sketchy. Most references describe the hardware electrically, but not acoustically — meaning they tell you what the bits do, but not what you actually hear.

So I decided to reverse-engineer the envelope system myself by experimentation, and create practical reference material for future sound design work.

Turns out the PSG’s “waveforms” are not really waveforms at all, but changes in VOLUME over time.

The result is the documentation shown above: a more human-readable interpretation of PSG Register 13 and the envelope timing system used by Registers 11 and 12.

As always: let me know what you think. Especially since this is not the usual DEVlog fare, but more of a technical deep-dive into the MSX PSG itself.

Greetings, Ron.

When development started, Cloaca Maxima was intended to be a dungeon crawler. Four characters, one sewer system, one mission.

The mission is still there. So are the sewers.

But somewhere along the way, the game found its story.

The four operatives Rome sends below the city are not heroes. They are expendable. Assembled from the compromised, the coerced, and the desperate. Each of them carries a history that Rome would prefer forgotten. Each of them sees the tunnels differently.

That difference is now at the heart of the game.

Cutscenes (short text scenes triggered by exploration and discovery) are told from the perspective of whoever is currently scouting ahead. Find the same object with a different scout, and you find a different story. The same tunnels. The same darkness. Four different ways of moving through it.

No moral lectures. No easy answers. Just four people descending into something Rome sent them to destroy, carrying everything they know.

Some of them may begin to wonder if Rome was right.