[Coco] SSC & MIDI

[Nick Marentes]

Fantastic news Jason and I think you definately have the talent to pull 
it off!

Yes, sound generation on the CoCo comes at a price. I have stuck to 
using the internal sound since this is what everyone has.

So far I am holding everything in balance with regards to game time and 
sound generation time.

The SSC cart is something I may consider at the very end but since I 
don't use a multi-pak, I therefore don't have the SCC attached.

(I own a multi-pak... I just hate it)

Midi is an option but that to me seems like an even bigger dongle than a 
multi-pak and SCC cartridge.

Besides, Midi is great for music but sampled sound effects may require a 
fancy midi device that supports samples.

I know back in the day, some Atari ST and Amiga games supported midi 
sound but they were all used just for the music.

It's a real shortcoming of the CoCo3 that they didn't provide a sound 
chip. Not only for better sound but also better speed for the 
application itself.

60 fps 1/2 pixel scrolling can definately be done and with CoCo 
generated sound. I'm confident that even when I insert the new tile 
system, I will still hit the mark. But it does stretch things once the 
rest of the game logic is added and your choice to look for another 
source for sound genetration is sound if you are aiming for 60fps.

At 60 fps, you may need to go for 1 pixel (4 screen) scrolling because 
it may be too fast at 2 pixel. It will be very smooth.

All the best and I look forward to see your progress.

Nick



On 22/06/2014 12:32 PM, jmlaw at iprimus.com.au wrote:
> As the SSC & MIDI topic has come up, I’ve posted some info on my 
> current project at the facebook group.
>
> The background is I’m trying to do a 60 fps 1 & 2 pixel horizontal 
> scrolling Super Mario Bros demo (may lead to more later). My focus 
> isn't so much on cloning it as I am wanting to learn about game 
> programming, and it's a great case study for that with lots of info 
> online. That said, I do intend to try to make it as accurate as I can. 
> With the tile updating, managing four pages, software sound just 
> wasn’t going to be enough to keep the frame rate up, so I’ve had to 
> consider some alternatives. Namely the SSC & DriveWire 4 MIDI.
>
> Now that you’re moving to tiles Nick, maybe something to consider if 
> you haven’t already?
>
> So here’s a copy of that for anyone not in the group who may find it 
> useful/interesting or whatever. Maybe it'll come up in someone's 
> Google list search some day...
>
> ***********
>
> I've been working with the Speech & Sound Cart for the Mario demo 
> background music (BGM). Studying everything I could find on Nintendo 
> Entertainment System (NES) music has taught me heaps about how to 
> apply software envelopes to the SSC generated tones to get a 
> near-perfect NES sound. Though using software envelopes you could 
> probably emulate the sounds of many other systems too.
>
> Not everyone has a SSC so I've also spent some time studying Aaron 
> Wolf's DriveWire 4 MIDI. I moused a short score of the Overworld theme 
> BGM in Robert Gault's modified version of Lyra and via Vcc 1.43b 
> (Becker port) and with the aid of the DriveWire spec, I've learned 
> enough to have it sounding the notes from my own code, but the timing 
> was off. Knowing I'd have to write the code to play the BGM which 
> controls the timing by frame (vsync interrupt) I figured I'll do the 
> SSC first then work out the timing for DriveWire MIDI in relation to 
> that. DriveWire MIDI via the Becker Port and the SSC work in a very 
> similar way so it's ideal. I wasn't going to mention this yet until 
> I'd done it all, but it's come up on the mailing list, so I may as well
>
> A few hiccups:
>
> The SSC requires a delay before sending a command after a reset or it 
> will be ignored. Unless I missed this, it's not documented anywhere. 
> From my tests, testing the status doesn't work in the usual way after 
> you first reset the SSC. I've narrowed it down to 285 cycles after a 
> reset before the SSC is actually ready for commands. 284 cycles you 
> just get allophones for the tone data sent as it ignores the direct 
> access to the AY-3-8913 command. My SSC model is the 26-3144A. I've 
> sent Simon my test binary for the delay, he has the other model and it 
> still works with a 284 cycle delay so it may be there's a ROM 
> difference between the models?? A simple delay loop after a reset 
> fixes this problem. I've extended the delay above 285 cycles just to 
> be sure.
>
> I also had trouble opening the DW4 MIDI channel. I was using the quick 
> version of the command, but could not get it to work after four nights 
> of trying. Maybe I misinterpreted the spec, but the longer open 
> channel command worked perfectly first go. What a relief
>
> I have the main melody square 2 (SQ2) channel playing from my own code 
> to the SSC, I have one more thing to fix then it's add the harmony 
> (SQ1), the baseline (TRI) and percussion noise (NOI) channels. A few 
> things to work out but should hopefully have a sample wav, a few more 
> pics & a vid soon.
>
> In the waveform pic, the top channel is the SQ2 NES, the lower the 
> SSC. This was just my first test. The background noise is greatly 
> exaggerated as I maximized the volume in the SSC recording to compare 
> it to the NES recording in Audacity (I have to adjust my envelopes). 
> The VU meter in the Mario pic is working for the SQ2 channel, the 
> others are just displaying test values until I write the code to play 
> those. They all update per frame and work in MESS & Vcc too, which is 
> great considering the timing required to run them, thought I'd have 
> issues with that.
>
> Ah and playback at 0.89 MHz as I haven't modified my SSC for the CoCo 
> 3 when run at 1.78 MHz yet, so you can play the BGM on a CoCo 2 also. 
> A semi-graphics VU meter of a similar style would be fairly simple in 
> comparison.
>
> So yeah, that's what I've been up to since the Mario scrolling vid, 
> (link in the comments of post with the level editor if you missed it).
>
> ***************
>
> I'm not claiming to be an expert on any of this by any means, I'm just 
> learning it myself and sharing what I've leaned to date. If I'm wrong 
> feel on any of it feel free to set me straight :) This is just my 
> experience. Bill Pierce is far more knowledgeable on MIDI than I am, 
> I'm just having a go.
>
> Thanks heaps Aaron for the DW4 and the MIDI and the Vcc Becker port, 
> it opens up some really nice options for game background music, maybe 
> even the sound effects, not sure haven't got that far yet. I'm a bit 
> worried there may be some noticeable lag re the latter but lets see...
>
> Thanks RG for the Lyra DW4 MIDI mod, helped a lot initially.
>
> Thanks Bill Pierce for the music/MIDI info on your site, first place I 
> started when looking into this :)
>
> Peace :)
>