Steam Community :: Video :: NES PCM 40kHz Demo - Infected Mushroom U R So F**ked RIOT Remix

> Videos > David Macintosh's Videos

NES PCM 40kHz Demo - Infected Mushroom U R So F**ked RIOT Remix

Award

Title

Description

Today, let me talk a little about the NES and its infamous DPCM Channel.

You may already know the fact that NES has 5 audio channels: 4 analogue and 1 digital. The digital one, called the DMC (Delta Modulation Channel) can output 1-bit delta-encoded or 7-bit directly loaded raw audio samples.

Many NES games began to use this channel mainly to play simple, short, not-so-audible samples, e.g. steel drums that appear in Super Mario Bros. 3. soundtrack. So why didn't they use it to play long digital samples as a whole BG music? The answer is simple: They use a lot of precious PRG space. It also explains why the vast majority of PCM samples have a low sample rate.

So I decided to create a PCM tech demo!

What you're hearing right now is a seamlessly looped part of a remix of U R So F*cked by Infected Mushroom converted to a long 7-bit 40000Hz mono audio sample and played directly by the NES DPCM channel. The ROM is 4 194 320 bytes (4 MiB) large and the audio data takes 99.6% of the whole ROM.

How it works?

All thanks to the UxROM mapper that is able to switch 16 PRG banks which gives us 2 MiB of total PRG space (256 PRG banks, 4MiB in total in NES 2.0 format). The audio was split into 256 16kib chunks, one per PRG Bank. Then, the main code loads the first PRG bank and streams all bytes by directly loading them to the PCM register from the beginning to the end of the bank. When the streaming is over, the RPG bank is switched to a next one and so on.

Credits for the music used in production of this demo belongs to Infected Mushroom (for the original song) and RIOT (for the remix): https://www.youtube.com/watch?v=21IJWFlsdjs

ROM Download: https://drive.google.com/file/d/12v1m90LZRhEJ68rRSk2o1rIocMarGYEF/view?usp=sharing

NOTE: The included ROM uses the NES 2.0 header format and may not be played correctly on emulators that don't support NES 2.0 format! I tested it on many emulators and only Nintendulator and Nestopia seem to run it properly (FCEUX has a tiny problem with PRG bank switching indexed above $03).

No audio tricks have been implemented in production of this video.

Save Cancel

19	Unique Visitors
0	Current Favorites