when hearing a bit of Atari Lynx music today, i thought to myself, “huh this mostly sounds like Sega Master System music, where it’s all just square waves, but it’s a bit more complex than that. what actually is this console’s sound chip?” Wikipedia just says “4 channel sound”, but further searching turned up an AtariAge forum post that described it as such:
It has a form of a linear feedback shift register (or LFSR) random number generator that has a length of 12 bits.
Bits 0-5, 7, 10, and 11 can be feedback taps. Each bit also has an output gate to XOR feedback.It was time-consuming for composers to get a decent waveform out of the LFSR synthesizer, so they just kept one feedback bit enabled, in which generates what is called "pure square waves". That's why most games tend to sound like a "Master System" at times.
The chip also had a mode for "integrated" output, which is just a form of random DPCM instead of raw noise. This just changed the amplitude of the DAC up or down over time. This would've been easier for "flute-like" sounds of those composers, as they can possibly simulate a triangle wave.The DACs also had a register for streaming 8-bit PCM audio. Klax and Qix are currently the only games I know that used PCM music.
this sounds absolutely buckwild for a sound chip design! i struggle to imagine how one would wrangle these synthesizers into doing reasonable‐sounding things. and yet, today i also found a new favourite obscure tune of mine by someone who managed to do just that within this console’s brief lifespan (though apparently this game went unreleased until 2004!), which i want to share: