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Discussing the Open Source FPGA Amiga Project
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 Post subject: Re: write here about software which makes problems until now
PostPosted: Sun Jul 15, 2012 11:22 pm 
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Posts: 479
I thought the high-tone problem in GODS was fixed a longer time ago? I can not hear any disturbing sound there.

But i would be happy, when anybody in the forum here could finally compare the scrolling of "SPEEDBALL 2" on a real Amiga-500 to the Minimig-Normal-Mode and then give a commend about it.


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 8:03 am 
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Posts: 349
Some of us old timer amiga users are a bunch of bssesive-compulsive freaks! :D

I'm talking about myself in the first place, WA72, don't get offended: but you and Imemust be the best examples around. :P

No, the high-pitch tone is still there: it's just less noticeable now because it's a lower-pitch tone, but it's there anyway.


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 9:46 am 
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Posts: 1568
Location: .de
It took a lot effort to get the Sigma/Delta Audio DAC in Minimig operating at this state.
Im not qualified to do any better fixing to this issue. At least the noise is much lower and in my testings it was no longer present.

The Speedball-2 comparison is done MANY times from my side. I could not detect any differences in scrolling.
If there was a big CPU<>Chipset timing problem, many other most critical title (demo) would show it too. But there is nothing like this.
I can not fix any problem, that isn't there ;)

If anyone has a solution, please let me know or build an own FPGA core :)

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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 6:04 pm 
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boing4000 wrote:
It took a lot effort to get the Sigma/Delta Audio DAC in Minimig operating at this state.
Im not qualified to do any better fixing to this issue. At least the noise is much lower and in my testings it was no longer present.

The Speedball-2 comparison is done MANY times from my side. I could not detect any differences in scrolling.
If there was a big CPU<>Chipset timing problem, many other most critical title (demo) would show it too. But there is nothing like this.
I can not fix any problem, that isn't there ;)

If anyone has a solution, please let me know or build an own FPGA core :)


Hello,

I have proposed a 3rd order Sigma/Delta Audio DAC somewhere on this forum.
I can confirm it works great on the Paula clone I put on my Amiga 2000.
A digital low pass filter had to be added too to make it sound like a real Amiga.
Of course, it takes more LUTs than the current implementation.
I did not try Speedball-2 yet. I will do it ASAP.

Regards,

Frederic


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 6:31 pm 
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Joined: Thu Jun 18, 2009 9:54 am
Posts: 349
Would it fit on Minimig 1.1 board?


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 7:41 pm 
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Posts: 341
frenchshark wrote:
I have proposed a 3rd order Sigma/Delta Audio DAC somewhere on this forum.


Yup - here http://minimig.net/viewtopic.php?p=5136#p5136

You mentioned the downside being the need for a 128 sample buffer for oversampling. Am I right in thinking that the window of the running average filter used for oversampling is actually narrower than a single sample at the speeds proposed? If so, am I right in thinking the buffer isn't actually needed, and all you need to do is keep track of when each sample edge enters and leaves the window?

I'm playing around with a delta-sigma DAC on a Cyclone 3 board at the moment, just for fun - so when I get a chance, I'll be interested to try out your 3rd order implementation.

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~ Amiga 4000/030 ~ Amiga 1200 030/50MHz ~ Turbo Chameleon 64 ~ Altera DE1 with Minimig core ~
Details of my projects: http://retroramblings.net


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Mon Jul 16, 2012 9:53 pm 
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MMrobinsonb5 wrote:
frenchshark wrote:
I have proposed a 3rd order Sigma/Delta Audio DAC somewhere on this forum.


Yup - here http://minimig.net/viewtopic.php?p=5136#p5136

You mentioned the downside being the need for a 128 sample buffer for oversampling. Am I right in thinking that the window of the running average filter used for oversampling is actually narrower than a single sample at the speeds proposed? If so, am I right in thinking the buffer isn't actually needed, and all you need to do is keep track of when each sample edge enters and leaves the window?

I thought about that too : IIRC, smallest period on an ECS amiga is 124. It is a good way to save some RAM blocks.
After some fiddling, the window is now 256-sample wide (actually, 248 samples because I need a small attenuation to not saturate the output driver).
248 gives : 3546895 / (2 * 248) = 7151 Hz cutting frequency. This is close enough to the real HW.
Without the filter, the sound is too metallic.
Moreover, by doubling the window one more time, we can easily recreate the LED filter at 3.5 KHz.
Maybe, someone can design a dual-mode filter that does the two different filtering based on the LED state.

Regards,

Frederic


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Tue Jul 17, 2012 2:13 pm 
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Posts: 349
I'm not an VHDL expert, nor am I asking anybody to do it, but... given frenchshark code for the filter is there, and Mmrobinsonb5 has a good idea for a smaller filter, wouldn't it be a good idea to implement that in the original Minimig 1.1 board and get perfect Amiga sound in the original Minimig board?

@Mmrobinsonb5: Would you do it if I donated you a new-in-box Minimig 1.1 board? I know you work on DE1 Minimig core improvements, but I don't know if you have the original Minimig board to twinkle with.


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 Post subject: Re: write here about software which makes problems until now
PostPosted: Tue Jul 17, 2012 5:07 pm 
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Location: .de
Please no audio low-pass filter as in real Amiga!
This sounds uggly and even Jay Miner was annoyed about this "Commodore feature".
All my Amiga model has a permanently disabled filter, no longer depending on LED state.

Better sound output is welcome, as long as it fits into the MinimigV1 FPGA.
Available blockram is almost fully used.

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 Post subject: Re: write here about software which makes problems until now
PostPosted: Tue Jul 17, 2012 10:30 pm 
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Joined: Tue Dec 13, 2011 7:48 pm
Posts: 341
gaula92 wrote:
@Mmrobinsonb5: Would you do it if I donated you a new-in-box Minimig 1.1 board? I know you work on DE1 Minimig core improvements, but I don't know if you have the original Minimig board to twinkle with.


Wow - that's a *very* generous offer - and no, I don't have a "real" Minimig board - but it seems like a lot of reward for what should (in theory!) be a fairly small amount of work!

Let me see how difficult it is to use Frenchshark's DAC first, and then see how difficult my modified filter idea turns out to be. (One complication is that each DAC will be converting the sum of two independent channels, so the length of time between level changes won't be constant.)

I *think* I can make it work, though (without using blockram at all) and if so, adding it to the Mniimig design should be pretty trivial, provided it fits.

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~ Amiga 4000/030 ~ Amiga 1200 030/50MHz ~ Turbo Chameleon 64 ~ Altera DE1 with Minimig core ~
Details of my projects: http://retroramblings.net


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