Music Monday: How NES Sound Works

Nick The Newbie is the public relations director for MAGFest, an annual video game music festival coming up January 13-16, 2011.

The sound on an NES is obviously lower in quality than something you’d hear on a CD, because recording audio into a digital format in the 80s and early 90s took up an inherently large amount of storage space, and storage was prohibitively expensive. You simply could not hold the 10MB/minute of music on a chip. If one could, instead, give simple parameters, a signal could be shaped and modified to give a desired sound with minimal storage required. This is the entire basis of synthesis, and is the general theory driving classic console sound hardware.

The CPU for the NES was the Ricoh 2a03, which handily included a programmable sound generator (PSG). This PSG had two square wave oscillators, one triangle wave oscillator, a noise channel, and a PCM (digital audio) channel. With these five outputs, an NES could effectively put out five individual sounds at once.

The square oscillators enabled modification of the volume, frequency (pitch), and widths of the peaks, and typically played the melody and harmony lines. The triangle wave had less flexibility, at least in terms of volume, and thus was usually used for the bass line, since it required less dynamics.

The noise channel was only capable of outputting static, and so varying bursts of static were often used for drum/cymbal hits as well as other sound effects. The PCM (pulse code modulation) channel was able to output recorded samples, albeit very low quality ones. This could put out some otherwise unsynthesizable sounds like voice samples (TMNT “Hey!”). Konami was rather clever in realizing the potential of the PCM channel, and often used it to store snare and bass drum hits, to give their music a little more character.

As you might remember from my special on Akumajou Densetsu, the NES and the Famicom are close, but not completely identical in sound hardware. There were additional pins on the cartridge slot which allowed for game manufacturers to add their own sound chips to famicom games, extending the capabilities of a lone famicom/nes chip.

Here are some expansion chips and games to go with them:

Konami – VRC6
-Added Channels – two square wave, one sawtooth wave
-Notable games – Akumajou Densetsu (Japanese castlevania 3), Mouryou Senki Madara

Konami – VRC7
-Added channels – six FM synthesis channels (similar to a genesis)
-Notable (only) game – Lagrange Point.

Nintendo – Famicom Disk System
-Notable games – Zelda 2, Metroid

FME-7 (Sunsoft 5 version)
-Added channels – three square waves
-Only game – Gimmick!

NAMCO106
-Added channels – eight additional channels, but quality degrades as more channels are used

Nintendo MMC5
-Added channels – two square waves.

There were quite a lot of games that never made it stateside due to the hardware differences, so make it a point to find the soundtracks that made use of these chips, and get rocking.