Bad Apple video ported to BBC Micro (Patreon)

If you're not familiar with Bad Apple, it's a a song from ZUN's Touhou game series. It was remixed and featured in a promotional silhouette video and quickly became a meme in the demoscene as a bar for video compression and streaming. Demo groups have been actively "porting" the PV to various computers and consoles, and the results have just been insane. There are Commodore 64, Atari  2600, even TI84 calculator versions of the demo, each with its own set  of technical achievements. There's also a version for the original IBM PC, written by Trixter, who may or may not have something to say in the comments... (hi Jim)!

Anyway, there was no port of the video to the BBC Micro (colloquially,  "Beeb"), a popular UK computer, until now. UK demogroup Bitshifters took it upon themselves to produce a version of the Bad Apple video that would not only replay on a BBC Micro but also do so smoothly in a Teletext mode exclusive to the machine and fit on a single floppy disk. They also needed someone to port the audio to the Beeb, which is where I came in. 

To properly understand the capabilities of the machine, it has a 6502  running at 2mhz with 32KB of RAM, perhaps roughly comparable to an Apple II+. The Beeb also has an SN76489 for sound which provides three channels of 50% square wave and rudimentary whitenoise that sounds like banging on trashcan lids. This chip first appeared in the TI99/4 (as the TMS9919 or SN94624), and also in several other systems like the  Colecovision, Sega Master System/Game Gear, IBM PCjr, and Tandy 1000.  There were various revisions. 

To properly get a song over to the BBC Micro, I first wrote an SMS song in Deflemask's PAL mode to get things as closely to our target as possible, and then we used additional scripts to convert the output to  the Beeb, mainly because the oscillator clock runs at different speeds between the two machines. Then we fine-tuned the errors out as best we  could. 

You can watch the final result here:  
bitshifters.github.io/posts/prods/bs-badapple.html 

One thing I found while working with this is that the diffferent variants of SN76489 — while the changes between revisions were extremely minor — might contribute to a lot of interesting bugs and errors. I'm already researching this more.

As soon as I have a good recording from a BBC Micro, I'll also release that, but in the meantime, I've released the Sega Master System version (which is slightly more bug-free) on my bandcamp, and thanks to your support, I have made it free:

http://inversephase.bandcamp.com/track/bad-apple-sms-sn76489

Grab yourself a free copy (Patrons, please enter 0 for the price) and let me know what you think! If you'd like, there are social media posts on twitter, facebook, and google+  that you can share with your friends and family.

Thanks for supporting!