> Additionally, it is possible to engage a low-pass 12 dB/oct Butterworth filter tuned at approximately 3.2 kHz by turning the Amiga power LED brighter with a special protracker command.
This didn't happen on the earliest Amigas. It just changed the power LED brightness.
I had one game (Psygnosis "Baal", otherwise fairly unmemorable) that flickered the LED with the beat of the title track just because it looked cool. It sounded awful on anything besides an A1000.
This is a classic "you ran out of pins / wanted a convenient debug feature, didn't you" design indication.
I'm slightly unclear on what the Paula pulse train would have looked like; is it what would normally be called a "1-bit DAC", or is it PWM at the PAL frequency?
IIRC when the machine crashed while playing sound, with the well-known blinking of the Power LED, you could hear the filter going on and off, too. And most games that had polished music turned the filter off.
> Additionally, it is possible to engage a low-pass 12 dB/oct Butterworth filter tuned at approximately 3.2 kHz by turning the Amiga power LED brighter with a special protracker command.