AMS I vs. AMS II
The original Advanced Music System was released in 1982. It required the BASIC cartridge to be inserted, limiting the amount of available RAM for songs. The Advanced Music System II came out in 1983 and did not require the BASIC cartridge. It also introduced memory-saving techniques such as built-in enveloping. Here, the original 1982 AMS is retroactively renamed to AMS I.
Importantly, reading an AMS I file into AMS II is not quite compatible. AMS II defaults to a non-flat envelope for each note, interfering with the original intention of the file creator. This might be a good default for straightforward, non-improvised AMS I files, but not for the AMS I files presented here. It is important to play AMS I files with AMS I and AMS II files with AMS II.
The Techniques
Pushing the Limits
• Enveloping (that is, in AMS I where it wasn’t explicitly provided, or custom enveloping in AMS II). This is accomplished by tying together notes of the same pitch but different loudnesses.
• Pitch-bending. This is accomplished by tying together notes of the same loudness but sequential pitch.
• Percussion. This is accomplished by playing a thirty-second note or shorter at loud volume in the lowest notes, where AMS applies a distortion value.
• Time-multiplexing a voice to simulate more than the four voices available. This is stealing a thirty-second note or shorter from the bass line for the percussion above.
Techniques
• Solos. Transcribing guitar and drum solos “by ear” rather than from piano sheet music (which omitted said solos)
• Vocals. Approximating vocals by mimicking duration and loudness of each syllable
• Color. Ensuring the blue-colored voice is used for the vocals to make it visually obvious which voice that was (for AMS I, especially, as in AMS II voice #1 was changed to blue).
Tricks
• Sound effects. Laser sound effect (really, a special case of pitch-bending). Also gongs and drum echoes.
Hardware and Software Limitations
The Atari 400/800 computers synthesized music, using its POKEY chip, in four voices — the number of notes that could be played simultaneously. POKEY did have the ability to add distortion, but it did not have hardware-supported audio envelope capability the way the Commodore 64 did (which came out three years after the Atari 400/800).
Software that came out years after AMS, such as AMP demonstrate what is possible with the hardware. But in terms of available music software, during our active years of 1982-1984, AMS was it, and so that is what we worked with. By far the biggest limitation of AMS is its lack of “subroutines”. Repeating bass and rhythm lines, which we spent so much time (and RAM) perfecting, just had to be repeated over and over again, consuming precious RAM.
A further limitation is the lack of an option to add distortion to the higher-pitched notes. There was a cutoff somewhere an octave or so below middle C where AMS had hard-wired a switchover from pure tones to slightly distorted tones. Having an option to apply distortion to higher notes would have allowed more flexibility in simulating various percussion.
Comparison: Galen vs. Conventional
In comparing the two renditions of “Tom Sawyer (Rush)” below, not only is it obvious in the beginning that Galen’s has percussion as well as a much more accurate synth laser sound effect, but Galen’s is also 99 seconds longer. The reason? Because he listened by ear for the drum solos and guitar solos, and included those. They are not present in standard piano sheet music, which is what was commonly available at the time in music stores, and which was conventionally used by most users of AMS.
Galen’s “Tom Sawyer (Rush)”
Conventional “Tom Sawyer (Rush)” by unknown file creator
Emulation
Way back in 1995, David Firth wrote a hardware-exact emulator of the Atari 800. To this day, it is still the most accurate.
Floppy disk “images” are 92K each and have the .ATR file extension. ATR images of the software can be downloaded for AMS I and AMS II. PDF of the user manual can be downloaded for AMS I.
Windows command line to execute AMS I
atari800 -osb_rom ATARIOSB.ROM -basic_rom ATARIBAS.ROM -basic_rev a -basic -atari -ntsc -nopatchall AMSI.atr
Windows command line to execute AMS II
atari800 -osb_rom ATARIOSB.ROM -atari -ntsc -nopatchall AMSII.atr
Where to Download
The AMS I & II files from this website can be downloaded from archive.org.
There are a couple of utilities to create or extract from .ATR files. We use atrutil.zip.
To load a large AMS I file, it is necessary to first launch the “Auxiliary program” (option J) from the main menu after starting AMS I.