What are Amiga samplers?

Over the course of the Commodore Amiga's active lifespan, a great many samplers (also known variously as sampler carts/cartridges, sound cards, audio digitisers, audio interfaces, etc) were manufactured to exploit audio capabilities that were unmatched by any other home computer of its time. In 1989 an Amiga 500 with a cheap 8bit parallel-port sampler gave you the means to produce professional sounding music in your bedroom for a few hundred pounds - about the same as it cost to hire a recording studio for a few days. Acid house and techno were exploding; hardcore, jungle and drum'n'bass were just around the corner. Even if your sample-based Amiga music wasn't quite professional sounding by the standards of audiophiles and hi-fi enthusiasts and the old-fashioned music industry, it was probably good enough for underground clubs and illegal raves! Countless dance, bass and electronic music superstars got their start with an Amiga and a cheap sampler.

Some samplers back then cost a lot of money and offered advanced features or higher quality than the rest, although there was (and still is) a fundamental limit to the sound quality it's possible to squeeze out of an Amiga. This project is a clone of the typical low-budget sampler design that flooded the market in the late 1980s and early 1990s. They're often referred to as 'carts', but they're actually not cartridges: they're usually small 25-pin parallel port dongles whose circuit boards and connectors are housed in the type of plastic shell that systems like the C64 and the VIC-20 used as cartridge housings. But some manufacturers called them cartridges, and we've been calling them carts for decades, so we'll stick with that. Some live in separate boxes attached by a parallel extension cable to the Amiga's printer port, and some connect to both parallel and serial ports, or even to a joystick port, as a hacky but clever way of getting up to 16bit resolution. Interesting stuff, but out of this project's scope for now!

The common features of these cheap sampler carts were:

• 8bit sample resolution
• Stereo or mono
• Typical maximum sampling rate of ~55Khz in mono (~37Khz for stereo)
• Usually claimed to feature impressive SNR, anti-aliasing filters, and special ~90Khz frequency modes (sometimes these claims were even true!)

The feature set of the Open Amiga Sampler is:

• 8bit sample resolution
• Mono
• Typical maximum sampling rate of ~52Khz
• Input amplifier with variable gain

In this documentation we'll explain how the OAS works, why and how we developed it, why we've chosen specs which appear to be lower than even the cheap samplers of the Amiga's heyday, and why that's actually a good thing!