I've been reading about the audio hardware in retro systems recently and I found an interesting opinion in one blog post I found. According to the poster while the term chiptune first appeared on the Amiga it isn't actually capable of them because it uses sample based hardware.
I didn't agree with this for various reasons but I thought I'd dig out the hardware reference manual and see what it said. I was quite surprised:
Paula is quite a capable girl, she can do:
4 channel 8 bit audio
2 channel 8 bit audio modulated by 6 bit volume (how the 14bit playback systems work).
OK, we all know that, but she can do much more:
2 channel 8 bit modulated by 6 bit volume at audio frequencies is known as amplitude modulation (AM). Analogue synth nuts know this as "ring modulation".
You can also have chains of modulation so channel 0 mods-> 1 mods-> 2 mods-> 3.
So your ring mod can ring mod it's ring mod. Complex stuff, I don't know of anything else that can do this other than modular synths.
Modulation of this sort is uncommon as it's highly complex but on the other hand chains of modulation is exactly how frequency modulation (FM) synths work.
Guess what? The Amiga can also do FM. The set up is the same as Amplitude modulation so you can have:
2 channels modulated by the other 2 channels.
1 channel modulated by a chain of the other 3 channels.
So the Amiga can act as a pretty complex FM monosynth, the limited bit depth and playback rate means it's not exactly going to be a DX7 but it will give it a grungy quality the DX7 (or any other FM synth) doesn't have.
But it gets better - Paula can have the FM and AM on at the same time. That'll allow über complex modulation and wave mutilation possibilities. I don't know of *anything* else that can do that sort of thing.
But back to the original question: Can the Amiga do chip tunes?
The question is really about is the Amiga used as a sampler or as a synth. Actually the Amiga can do both.
The Amiga normally plays back samples but these "samples" can also be computer generated waveforms. It is thus quite capable of doing pure synthesis (known as wavetable synthesis).
The Amiga has been doing this from the very beginning and it's still done today, If you use the Octamed synth waveform editor you are using the Amiga as a wavetable synth, indeed this appears the term chiptune probably came from the use of this feature.
You can use the Amiga for sample playback but even here it has special "features". Actually they're not features but limitations of the system that give it a unique sound.
Paula plays sounds by playing 8 bit samples from memory, but it does it in an interesting way. Most systems (including mixed Amiga audio) work by mixing the waveforms together and playing them through a pair of channels at a fixed frequency.
The Amiga doesn't do this, it plays different notes by changing the playback speed of the samples. This isn't unique (the PPG Wave synth did the same) but the limitations of 8 bit and low sampling frequencies combine with this have an interesting effect.
Early Amiga mods had to fit on a disc so samples often used a very low sampling rate. I seem to remember a lot used to be around 8KHz in the old days.
The problem is 8 bit sounds suffer from quantisation noise. When you sample at too low a rate (like 8KHz...) you also get aliasing noise. These are quite noticeable on Amiga audio samples when you compare it to a modern system.
The interesting bit is because of the way the Amiga speeds up and slows down samples to play them, it also speeds up and slows down the noise. The noise isn't just in the background, it becomes part and parcel of the Amiga sound.
I don't know if any of the Amiga emulators or even things like minimig etc. try to emulate this effect.
So, all in all the Amiga has a much more powerful audio system than you might think.
Because of the ability to play samples, I don't think Paula has ever been pushed to see what she can do. Unlike say SID on the C64 which has been investigated throughly.
Clearly Paula is capable of some highly sophisticated synthesis with FM, AM samples and wavetable capabilities - all of which could conceivably be used at once. Then of course is the 68K itself which unlike the 8 bit micros got upgraded, there's nothing from throwing some real time sample generation or wave manipulation into the mix as well.
So, yes the Amiga can do chip tunes, but it's capable of much, much more. Far more than we ever used it for.
Oh, BTW Paula can also do a 1.7 MHz (yes that's MHz) carrier thing...
