Signal Carnival

At Revision 2025, we released "Signal Carnival" (csdb, YouTube). This demo asks you to switch the audio and video cable of your C64: (Diagram by Felidae) Technically, "misplugging" those cables is not a completely new idea. In the 90s, it was a common thing to connect audio to both speaker and video, to get screen flickering timed with the music beats. However, "Signal Carnival" is the first production to switch both these cables, while still being able to play meaningful audio and video. How to drive audio using a video signal The C64's VIC chip operates at a frequency of 7.9Mhz, and new values can be written to it by the 6502 at a rate of up to 246kHz. Since even high quality audio rarely exceeds 44kHz, this is easily a high enough frequency to generate music. Inspired by the music routine from freespin, we combined two timers to get an interesting waveform, which is adjusted once per frame. This is the code that drives audio: lda $dc06 ora $dd06 eor $02 sta $d020 Here, $dc06 ... Read full article.