Negative Charge

Refining the Acorn Electron 1-bit sound. Spent a lot of time in the debugger measuring cycles. 🔊 youtu.be/D3JL4Qk4Mhc?...

C64 SID Playback on the Acorn Electron This is better! I used the same output routine from the PT3 player for 1-bit sound, and it's a significant improvement. Shouldn't make your ears bleed as much. 😂🔊

Returning to the Acorn Electron and my ongoing mission to get better sound out of it... I've taken the Vortex II PT3 player engine from the BBC Micro player I put together and created a new 1-bit Electron ULA stage to dynamically play the PT3 files. Sounds better than the SID attempt so far. 🔊

Thought I'd try converting one of the newer Atari ST SNDH tracks to the BBC Micro, and now wondering whether I can produce something like AmigAtari for the Beeb (www.pouet.net/prod.php?whi...). First I want to take a look at digidrums and sample playback. 🔊

So, I kicked out the OS and employed all 4 6522 VIA timers to map to envelopes plus the three MFP timers to bring Mad Max's (Jochen Hippel) famous track "There Aren't Any Sheep in Outer Mongolia" from the "Ooh Crikey Wot A Scorcher" Atari ST demo to the BBC Micro as it should be heard. 🔊

Here's a second Atari ST YM2149F tune converted to the BBC Micro SN76489. This one uses both hardware envelopes and timer effects across all three MFP timers that have to reproduced in software / 6522 IRQs on the BBC. There are a few glitches due to CPU demand, but working on reducing that. 🔊

Things the BBC Micro SN76489 shouldn't be able to do - Part 2 So it's possible to create a basic software emulation of the SID chip. Now, what should be an easier task of emulating the YM2149F, as we're dealing with square waves and hardware envelopes, but also MPF timer effects - it wasn't. 🔊

So... this shouldn't really be possible (and to some degree it isn't), but here's a version of my SoftSID emulator that plays C64 SID files now running on an Acorn Electron on it's ULA... 1-bit sound... on and off. Carrier noise and artefacts, but it's running.... ⚠️🔊 Turn down your speakers!⚠️

A few more updates... starting to look more like a game, but still a little too slow to be playable. Added in opponent cars - sprites are all placeholders (as is the music). Included code from one of my old sample players as well. I may remove the road shading to see if I can get more speed. 🔊

A quick palette change at the top half of the screen (leaves no longer changing colour at the horizon), and a fix to the disappearing trees, along with better tracking of road curvature and height. Next to see if I can add opponents to the track without severely impacting performance. 🔊

A little more progress... the music is in, added some trees (which randomly disappear at the moment, and don't look right above the horizon due to the palette change) and a mountain range. The small map (you might recognise it) will eventually mirror the curves on screen, but not quite working yet🔊

...and here's what I'll be adding next. Rather than play back the complete SID file I've extracted the original sequencer from the C64 driver (order lists -> patterns -> notes/commands) so I don't have to dynamically convert the SID frequencies to the SN76489. Let's hope there's enough space! 🔊

A few updates.... horizon moved to middle of the screen, now has three lanes for the road, dithering improved and applied to grass too, and added some clouds (which don't move at the moment). It's slightly slower but working on reclaiming cycles. Here's the code running in the beebjit emulator:

Not sure where I'm going to go with this, if anywhere at all. Interesting experiment to try and get the ideas from here working on the BBC Micro: www.extentofthejam.com/pseudo/ E-Type (www.bbcmicro.co.uk/game.php?id=...) was pretty good, but was always a little disappointed by the viewport size.

A few updates to the SID emulation on the SN76489. Playback speed is better. I'll put all three players (SoftSID, HardSID & NoSID) up on GitHub soon. Just sorting out the automatic memory relocation to filter out digi tracks these players can't yet handle. 🔊

Just a small update, but I now have 4x speed SID files dynamically playing on the SN76489. Cycles are very tight so I had to disable the scope and colour cycling, but sounds good. 🔊

Added in IRQ software bass by default... this is less harsh than using periodic noise via the LFSR. Also improved the scope visualization a little. Still lots of issues with SID files that trample all over the BBC Micro memory map, but this one appears to work just fine. 🔊

I've posted many C64 SID to SN76489 conversions previously. These are pre-processed register dumps with large memory footprints and need compression / SWRAM. What you're seeing here is actual SID playback with dynamic SN76489 conversion. A game changer thanks to @kieranhj.bsky.social's AKS work.

Inspired by @kieranhj.bsky.social 's realtime AKS player on the BBC Micro, I reused the AY-3-8912 to SN76489 converter to expand this to realtime playback of PT3 files from Vortex Tracker. This opens up another tracker that can now be used for BBC Micro music composition. Much smaller than ym files.

A little side project I've been working on... a lightweight streaming ZX02 music driver for the BBC Micro. Supports main memory as well as multiple chunks spread over SWRAM banks. Without giving too much away, the ultimate platform for this driver isn't just the SN76489... more to come 🔊

A bit of a diversion from SoftSID. I realised that with a few minor changes I could add support for the BeebSID device which interfaces with a hardware SID. Also added a rudimentary menu system and tools to automate the batch relocation of SID files. Should be ready to publish to GitHub soon. 🔊

Added a rudimentary oscilloscope view to the BBC Micro SoftSID player. It takes up cycles which means I have to drop sampling down to 6500hz, but @pauliehughes.bsky.social SID driver still sounds good on hardware and a sound chip it was never supposed to work on 😊🔊

Working on getting some of the more complex SIDs playing. Created a Mode 7 version to free up more base memory, and updated the command line parsing to allow loading from any drive. Still some problematic SIDs that relocate to memory regions not writable on the BBC Micro which need recompiling.

A little more progress on SoftSID for the BBC Micro. Thanks to @kieranhj.bsky.social for testing on real hardware, which highlighted subtle inconsistencies on all emulators... they may sound fine, but the real hardware doesn't like it when you try an over-optimise the writes to the SN76849.

Here’s the complete Monty on the Run SID playing back using SoftSID on the BBC Micro (albeit slightly too slow). Trying to work out what’s causing the high-pitched carrier tone on other emulators - BeebEm is surprisingly the best right now. youtu.be/2Pw7LqgPdTI

BBC Micro SoftSID v0.03 Now working on other emulators, and directly parsing relocated .sid files. This is the track I've always wanted to get playing properly on the BBC Micro. Getting closer.... 🔊

Just to prove to myself that playback of other SID files via the SoftSID, here's Plastic Pop by Danko 🔊

SoftSID v0.02 for the BBC Micro This is a bit more like it. Upped the audio rate to 6.1 kHz to match the VIC-20 version. Also re-located the SID to &1100 which was the cause of the random hangs and inability to playback on the Model B due to a DFS clash. I need to relocate a different SID now 😊🔉

I previously had a go at converting Tim Follin's 1-bit ZX Spectrum beeper routine for Agent X II to the BBC Micro's SN76489. Here's a follow up attempt with Chronos. The percussion isn't quite right, but the melody is perfectly recognisable. 🔊

Just to close this one out... random colour palette, screen fades and the odd teapot. Source code at the link below for those interested. I'm sure it can be optimized and even implemented in a better way. github.com/NegativeChar...

I haven't posted any demos for a long while, so here's a version of 2D Pipes in Mode 2 which works as quite a good screensaver for the BBC Micro. No music on this one as I waste 20kb just on the screen mode. No random teapots at the moment either. It might look better in Mode 1 with square pixels.

I've replaced the compression with zx02 from lzss, which on average is giving 2kb smaller files. I've also implemented a new SID converter to handle some of the trickier tunes. Doesn't look any different, but I can now squeeze a few extra tracks onto the BBC Micro music disks. 🔊

Slowly putting together some new music disks for the BBC Micro using a new set of converters. This one demonstrates squeezing a multi channel song down into 3 tone channels and one noise channel. Still some refinement needed. Here's the original for comparison: demozoo.org/music/134849/ 🔊

Putting the BBC Micro compressed VGM to the side for now as I can't get it to work at the required speed. Instead, I've been looking at some of the Tim Follin archives posted by @breakintoprogram.co.uk to GitHub to see if I can get any of the classic beeper music playing back on the SN76489: 🔊

While I continue to battle with compressed VGM playback streaming from disk at a decent speed, here's some brand new BBC Micro music by Enfys from Outline 2026. 🔊

Some progress! I now have compressed VGM files (.VGZ) streaming from disk and decompressing on the fly. How do I know it's working? At the very end of the clip you can make out the GD3 strings. Very close to having a streaming, decompressing, SN76489 VGM playback engine. 14KB expanding to 95KB.

Buffer size reduced to 2kb which leaves plenty of memory for vgz decompression. 8271 floppy disk controller support fixed. 60Hz VGM playback fine. So now I'll work on a basic streaming decompressor to a ring buffer for VGZ. The window should be 32kb (which I don't have free) but we won't need that.