Commodore 64 SID Oscillator Behaviour (Especially "Random" Noise) LFSR

Let's explore how the Commodore 64 SID (Sound Interface Device) oscillators behave, with special attention to the noise ("random") oscillator. We attempt to simulate the 23-bit Linear Feedback Shift Register with a BASIC program, and then fiddle with the SID's test bit to reset the oscillator and make it match the simulation. Robin From The Future also shows up to let you HEAR what these waveforms sound like on a real C64. The original cut of this video didn't have any SID audio!! Kinda weird experimental stuff! To support 8-Bit Show And Tell: Become a patron: https://patreon.com/8BitShowAndTell One-time donation: https://paypal.me/8BitShowAndTell 2nd channel: https://youtube.com/channel/UCAgWzEh5c8391eJnELDy9OA End credits music is "Confounded to Corruption" by Bedford Level Experiment. Here's an earlier mix of it with C64 visuals: https://youtu.be/U1VKwqUWYa8 Download the .d64 with the BASIC code: https://8bitshowandtell.com/downloads/sidlfsr.d64 Waveform diagrams from Chapter 4 of Commodore 64 Programmer's Reference Guide: https://archive.org/details/c64-programmer-ref/page/n213/mode/2up Interesting reading on the noise waveform: http://www.oxyron.de/html/registers_sid.html https://csdb.dk/forums/?roomid=11&topicid=118693&showallposts=1 https://codebase64.org/doku.php?id=base:noise_waveform http://www.sidmusic.org/sid/sidtech5.html https://web.archive.org/web/20220703212619/http://www.dekadence64.org/sidwav.txt https://web.archive.org/web/20150406004628/http://sid.kubarth.com/articles/interview_bob_yannes.html Linear Feedback Shift Registers article on Wikipedia: http://en.wikipedia.org/wiki/Linear_feedback_shift_register Optimal taps to choose for different length LFSRs on Page 5. NOTE: the bit numbers in this document are 1-based while I've used 0-based bit numbers in this video. Subtract 1 from the numbers in the document for use in my BASIC program. https://www.xilinx.com/support/documentation/application_notes/xapp052.pdf Index: 0:00 SID Oscillator 3 Output Program 3:42 Triangle Waveform 5:45 Robin From The Future 8:38 Sawtooth Waveform 10:07 Pulse Waveform 13:48 Noise Waveform 16:31 Internal 24-bit Oscillators 18:48 BASIC SID LFSR Simulation output 21:40 BASIC code walkthrough (section 1) 24:30 Explaining the taps 28:38 BASIC code walkthrough (section 2) 31:50 SID Test Bit: Resetting the oscillator 35:35 Is this riveting or what?? Trial & error. 41:49 Future ideas: SuperCPU? 45:00 Thanks!