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Help: Sound difference in Master System VDP revisions?
Post Posted: Sun Jun 24, 2018 10:17 am
Does anyone have the original Master System with SMS1 VDP or Game Gear? Can you please record sound for me?

http://www.smspower.org/forums/17116-SMSTestSuiteWorkInProgressHomebrew
Download TestSuite.rar (version 0.14) from that thread. Go to Audio Tests and record little bit of the noise channel sound.
Doesn't matter if it's NTSC or PAL.

These are my recordings from my own hardware:
https://www.dropbox.com/s/0ychqy8avry4lee/VDP_PSG.rar?dl=0
Mega Drive recordings have a much louder noise bassdrum. Why is it like this? Using the ModelTest.rar from that thread tells me that my Mega Drives have SMS1 VDP while my Master Systems have SMS2 VDP. Could that be the reason? I haven't heard SMS1 VDP Master System or a Game Gear yet, I'm curious what do they sound like?
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Post Posted: Sun Jun 24, 2018 11:23 am
Last edited by Maxim on Sun Jun 24, 2018 12:10 pm; edited 1 time in total
I suspect it's to do with the analogue filtering applied, recording directly from the video chip pins ("prosound" style) probably makes it sound more similar. Similarly, listening on the same system via RF or AV outputs will probably be a bit different too.
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Post Posted: Sun Jun 24, 2018 11:56 am
Filtering probably does play a part also, I would like to hear direct audio recordings of course too.

OK, I did more tests... I recorded all the 16 different volume levels from both SMS & MD. Then matched the volumes as well as I could.

The loudest levels on Master System are almost the same. On Mega Drive there are much bigger gaps between the high volumes. What I can hear is that SMS & MD volumes are pretty much equal until the third loudest volume level. How do the volumes work again with the PSG, 0 to 15, 0 being the loudest? If so, then the volumes differ between SMS and MD like this:

0 (like double as loud on MD)
1 (much louder on MD)
2 (slightly louder on MD)
3 to 15 (similar volume)

This explains the louder noise bassdrum on my recording. As it's the only instrument in the loop that has full volume. I also quickly tested one of my tracks by changing all the high values to a lower value, it started to sound more similar on MD then.

I still really want to know how these volumes work on original VDP1 SMS and Game Gear? Sorry I'm in a hurry at the moment, but I can upload more examples and pictures later maybe.
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Post Posted: Sun Jun 24, 2018 12:17 pm
Each volume level (attenuation) is 2dB quieter than the previous - or at least, that's what the docs say. This means the gaps get smaller as it gets quieter.

Many years ago when making in_vgm I recorded the sounds using constant tones at each level, via RF from my SMS 2, and saw much the same as you.
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Post Posted: Mon Jun 25, 2018 7:55 am
TomyS wrote
Using the ModelTest.rar from that thread tells me that my Mega Drives have SMS1 VDP while my Master Systems have SMS2 VDP.


that ModelTest ROM was just a quick test, it doesn't give any meaningful info on a MegaDrive.
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Post Posted: Mon Jun 25, 2018 5:32 pm
Regarding PSG volume levels I'll link this post of TmEE where he shows what's wrong with the SMS 2.
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Post Posted: Mon Jun 25, 2018 7:47 pm
Can someone more knowledgeable than me comment on the merits of http://little-scale.blogspot.com/2008/06/how-to-prosound-sega-master-system-2.ht... ? My guess is that it is missing something important, like isolating the pin and boosting the levels to the correct scale, as well as the current sourcing in the linked post.
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Post Posted: Wed Jun 27, 2018 10:38 am
ValleyBell wrote
Regarding PSG volume levels I'll link this post of TmEE where he shows what's wrong with the SMS 2.


Thank you for the link, yes this is exactly how my SMS2 behaves! TmEE also writes: "No such problem on SMS1", but the same problem also affects my SMS1.
So some original Master Systems have the correct volume values and some do not?

I think it's best to make PSG music without the 3 highest volume values then. This way the sound balance is close enough between any console variations. At least it's finally great to know the reason for this difference.
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Post Posted: Wed Jun 27, 2018 12:59 pm
Could always allow the project the track is outputted for to allow selecting between a 'louder' and a 'quieter' set of tracks, depending on the hardware.

Best of both worlds, if it works out correctly.
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Post Posted: Thu Jun 28, 2018 5:33 am
ValleyBell wrote
Regarding PSG volume levels I'll link this post of TmEE where he shows what's wrong with the SMS 2.

Reposting for preservation:
TmEE wrote
PSG doesn't clip.

What the document says is also not clipping but flattening of the PSG output from insufficient resistor value in SMS2. The output can only sink current and requires external resistor for sourcing (or was it opposite, I don't remember), and that resistor is little too high value in SMS2. No such problem on SMS1 or MDs. When that resistor is too low value the volume step goes higher, beyond 2db per step.

Bad resistor :
Image
Correct resistor :
Image

964A21FD-9555-4724-B919-78E592D6DADF.jpeg (94.54 KB)
Good resistor
964A21FD-9555-4724-B919-78E592D6DADF.jpeg

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