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Discussing the Open Source FPGA Amiga Project
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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Nov 11, 2012 10:58 pm 
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Joined: Tue Dec 13, 2011 7:48 pm
Posts: 341
And here's the core:
Attachment:
2ndOrder1.zip [94.59 KiB]
Downloaded 120 times


Edit: Nuts, the page has turned!
@Chaos, have a look at my previous post - I'm seeing some odd effects with this. I might have messed something up in getting it to work on the Minimig - but I didn't touch the modulator itself, it was just a matter of plumbing it in...

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Feb 10, 2013 7:13 pm 
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So today I've been trying to improve my 2nd order SD design, and the results are at least on the right track ;)

First I tried to implement the sigma-delta in a C model, and I can honestly say that the results of the processed sounds through the model are indiscernible from the original with just 128x oversampling, so at least the model is pretty good. ;) (Pro audio DACs usually use 5-stage SD, and can achieve perfect conversion with just 64x oversampling.) Here are links to some samples processed with the C model:

https://dl.dropbox.com/u/524989/BarryLe ... _MODEL.wav
https://dl.dropbox.com/u/524989/BruceCo ... _MODEL.wav
https://dl.dropbox.com/u/524989/Karsten ... _MODEL.wav
https://dl.dropbox.com/u/524989/MartinG ... _MODEL.wav
https://dl.dropbox.com/u/524989/Patrick ... _MODEL.wav
https://dl.dropbox.com/u/524989/Porcela ... _MODEL.wav
https://dl.dropbox.com/u/524989/TimFoll ... _MODEL.wav
https://dl.dropbox.com/u/524989/TimFoll ... _MODEL.wav
https://dl.dropbox.com/u/524989/TimFoll ... _MODEL.wav

I also played some MODs on the FPGA itself, here are the links:
https://dl.dropbox.com/u/524989/Enigma_FPGA.mp3
https://dl.dropbox.com/u/524989/GauntletIII_FPGA.mp3
https://dl.dropbox.com/u/524989/GuitarSlinger_FPGA.mp3
https://dl.dropbox.com/u/524989/Stardust_FPGA.mp3
https://dl.dropbox.com/u/524989/UnrealII_FPGA.mp3

The FPGA output has a slight high-pitched tone present, I believe it's probably my power supply and/or recording setup. I'll look into that later. I also tested the game Gods, and I didn't hear any spurious noises after jumps, picking up stuff etc.

What's changed:
- I used MMrobinsonb5's silence fix (thanks!)
- the input of the SD is passed through a 16-stage linear interpolator
- all bits of the input are used, so no dithering is applied
- I improved the quality of the noise generator by using two independent LFSR PRNGs, which are combined and slightly high-pass filtered and they give a pretty good HP triangular-shaped PDF noise
- the random noise is applied directly before the quantizer, which will help randomize the 1/0 output of the SD, but should not be detectable, as the error feedback will in this case cancel it out
- some noise-shaping is applied to the error feedback signal

Like I said, the SD will probably need some further fixes, or it even might not work out at all. In any case, I attached the Audio.v file for anyone interested.

Enjoy!


Attachments:
Audio.zip [6.47 KiB]
Downloaded 102 times

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Feb 10, 2013 8:25 pm 
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Joined: Tue Dec 13, 2011 7:48 pm
Posts: 341
Nice work - sounds pretty good at a first listen! I hear the background sound too, though - it seems to be some kind of idle tone at 200Hz and goes away if even very quiet sounds are playing.
Here's a frequency plot, which apart from the background tone looks very good:
Attachment:
FreqPlot.jpg
FreqPlot.jpg [ 110.76 KiB | Viewed 1487 times ]


@gaula92: over to you my bat-eared friend!
Attachment:
Chaos2ndOrder_20120210.zip [104.12 KiB]
Downloaded 117 times

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Feb 10, 2013 8:43 pm 
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Posts: 313
MMrobinsonb5, thanks for trying it!

Looks like the background sound is real, not just in my head :) (or a result of my power supply). The C model is more or less a complete emulation of the FPGA sigma-delta, and I can't hear any weird noises, so it could be something wrong with either my implementation in Verilog, or a weird combination of some unknown factors. Will look into that!

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Mon Feb 11, 2013 12:18 am 
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Joined: Thu Jun 18, 2009 9:54 am
Posts: 349
This version sounds good but the background noise is annoying :D
Thanks for the testing core, MMRobinsonb5, and for your efforts on this, Chaos!


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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Mon Feb 11, 2013 10:52 pm 
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Location: .de
Agreed, also Gods has again a short error noise at char jump.
This was totally gone in last Audio.v module, that I used in the 130117 release.

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Mar 10, 2013 1:40 pm 
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I just edit the working Audio.v module and "fixed" the reset behaviour.
Synthesized core works like before (no side noise in Gods or other title).


Attachments:
Audio.zip [6.01 KiB]
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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Sun Mar 10, 2013 3:37 pm 
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What reset behavior, Boing4000? I haven't noticed anything like that with your last core revision with TURBO set at 28MHz (from viewtopic.php?f=5&t=557).


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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Mon Mar 11, 2013 10:03 am 
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Location: .de
There was a (!n_reset) in the sources permanently defined at 1'b1 and a comment like "// fixme reset behaviour".
This is now gone because it was not needed at all.

Minimig sound the same but FPGA now has a bit more free space inside ;)

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 Post subject: Re: Minimig Sigma-Delta and the noise in Gods!
PostPosted: Wed Mar 13, 2013 7:04 am 
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Joined: Fri Jan 20, 2012 9:32 pm
Posts: 55
Guys,

Have anyone try to look if all that issues high pitch sound, not silenced DAC are not related to missed attach functionality in an audio module imlementation? It would be nice if someone could take a look how an audio HW is configured to play GODS music at the end of that "corupted" tones.


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