Minimig Discussion Forum

Im offering help/test/cooperate in implementing the DAC in the MinimigV1.
Currently it seems to be a bit hard (to me) to implement the code in the core structure.
If its done, its ready for testing and adjustments

Now that you are telling that, I remember that was one reason I did not explore that path.
Another reason is that the 6-bit volume change is not synchronous with the 8-bit sample change.
Potentially, you can get quite some 15-bit sample changes over a 256-cycle window.

On the other hand, putting only the new DAC is quite trivial but you will get that metallic sound.
You can try also a simpler 1st order IIR filter. The article from Antti Lankila gives some good hints : http://www.bel.fi/~alankila/modguide/interpolate.txt

Regards,

Frederic

Ah yes. (Fun fact: the Amiga's volume control was apparently implemented as a PWM gate on the audio path.) I would imagine registering the volume transitions to become synchronous with the sample edges would be possible, though, and wouldn't impair accuracy to any great degree.



Indeed - I've got the DAC itself working on the cheap EBay CIII board I've been using for experimentation.

The output of the 3rd order filter seems rather attenuated compared with the simple 1st order filter I've been playing with, though. Is this a side-effect of the algorithm, or a deliberate choice to keep the output at line level when driven from 3.3v?



Ah thanks for that - I've just had a quick peep, and there's some good info there.

Edit: by the way, is there a practical upper limit to the frequency at which a sigma delta DAC can run before imperfect waveforms on the output pins of the FPGA become an issue, or is it OK in practice to run them at near the fmax?

I noticed that too, I think it is a side effect of the algorithm. You can play with the quantizer :
assign w_data_qt_p2 = (r_data_fwd_p2[23]) ? 24'hF00000 : 24'h100000;
Be careful of not saturating the computation.


Since it is a passive RC filter, you will always get imperfect waveform, switching at many MHz.
I ran mine at 85.9 MHz without any problem. It might get tough on the I/O drivers.

Regards,

Frederic

I suggest the DAC discussion would better fit in the Development thread

Good point - the next step for me is to try and get some FFT plots , so if no-one beats me to it, I'll start one in the Development forum when I'm ready to post them.

I have news here to some of the few games, which can not be loaded until now on the Minimig.

The two games "ARCADE POOL" and "THE DEEP" don`t work at all on the Minimig, when normal Diskversions of them was used.

But especially "ARCADE POOL" is a great game, which i also wanted to play on my Minimig.

So, yesterday i created some "Loader-Disks" for this games and i was successful in making this two games work now.

The game "ARCADE POOL" works perfect now with this Loader-Disk. No problems at all. It just has 2 Disks now, instead of 1.

The game "THE DEEP" has massive problems with the loading-process on the Minimig and until now, also freezing the game, just resulted in a blackscreen. But now with this Loader-Disk here, i succeeded in making a workable ingame-freeze and it´s normal playable now. Sadly, when you lost all lifes, the game don`t go back to the game-menue, but rather hangs in a blackscreen then. So the Minimig must be resetted to play again. Not perfect, but better than nothing, because the game itself works perfect, just when you finish a game it hangs.

So here are the Minimig Loader-Disks for this two games. Just rename from pdf to adf and use the Minimig-settings, which was written as instructions in the Amiga-DOS in the files itself.