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Re: ay8910 [Re: Dr.Venom] #92271 01/11/14 09:29 AM
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Dr.Venom Offline OP
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Originally Posted By Dr.Venom
Could this be the culprit?


Hmm.. setting them all to zero disables the ay8910 output/volume, but the offset remains. Guess it has nothing to do with it then. I'll stop making wild guesses now, lol wink

Looking forward to the implemetation of the mixing stage. If there's anything that I can test or provide more examples from real MSX, just let me know..

Re: ay8910 [Re: Dr.Venom] #92306 01/14/14 12:37 AM
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Originally Posted By Dr.Venom
Originally Posted By couriersud
The whole mixing as done by the MSX hardware causes such an offset. Just connect an oscilloscope to the MSX sound output.

Would the same argument apply for the two MAME drivers, Bombjack and Nemesis, that I quoted in that message? I can't help but feeling that it seems "suspect" that only the drivers containing the ay8910 (be it in MESS or MAME) seem to have these offsets, but not others.

On the Audacity site the cause for a DC offset is said to be (almost always) a fixed voltage offset somewhere in the audio chain. That page also lists the problems that a DC-offset introduces for sound quality.

Quote:
"The cause is almost always a fixed voltage offset somewhere in the audio chain before the analog signal is converted to digital values. For example, the voltage may be directly caused by a faulty sound card, or may come from some other device that is attached to the card. Any offset is normally so small as to not be noticeable, but with defective or poor quality hardware it may become large enough to be a problem. "


Interestingly I see that a fixed voltage offset is purposedly introduced in the ay8910 driver:
Quote:
"For the AY measurements cited in e.g. openmsx as "Hacker Kay" for a single channel were taken. These were normalized to 0 ... 65535 and consequently adapted to an offset of 0.2V and a VPP of 1.3V.

Could this be the culprit?

If so, what changes would I need to make to remove that voltage offset in the source code? Just so that I can re-run the audiogram test.


Originally Posted By Dr.Venom

MAME Nemesis ay8910:


MAME Bombjack ay8910:



The AY8910 does *exactly* output what the original did. Even with the netlist code you'll get an offset. That's been the design. The only difference will be, that we burn millions of cpu cycles to amplify the - if I remember correctly - 1 to 3 volts to hmm- say - 2 to 12 volts. Well, you'll get some decay from the 8255 sound output. somebody needs to tell me the value of C55, though.

Any sound signal for which limit(t->inifinity, "avg"(0, t, f(t)) = 0 is produced after the msx schematics end - at least those I digged out on the internet.

Just onnect an oszilloscope in "DC" mode to the sound output :-)

Re: ay8910 [Re: couriersud] #92309 01/14/14 09:03 AM
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Dr.Venom Offline OP
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Originally Posted By couriersud
Just onnect an oszilloscope in "DC" mode to the sound output :-)

Unfortunately I don't have an oscilloscope, maybe one day. Regardless, I believe you :-)


Originally Posted By couriersud
somebody needs to tell me the value of C55, though.

Where do you see C55? I can't see it on the NMS8245 schematics (or the NMS8250/55). Possibly you have a link for people to look at?


Re: ay8910 [Re: Dr.Venom] #92313 01/14/14 07:09 PM
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Here the link:

http://msx.hansotten.com/uploads/msxdocs/STM-A_SVI318-328.pdf

The capacitor actually is not annotated (sorry,) it is on page 9 quadrant D7.

The NMS8245 schematics are different. Sound signals passes through a high-pass filter before mixing. And after the amplifying transistor is a DC-block capacitor.

Thus, on this model the sound output should be DC-free (Audio on Scart connector). No need to buy an oscilloscope :-)

Re: ay8910 [Re: Dr.Venom] #92320 01/14/14 07:57 PM
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So basically every MSX model sounds different? smile

Re: ay8910 [Re: Dr.Venom] #92321 01/14/14 08:08 PM
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hap Offline
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Yeah, volume balance differs often between models. I'd love to see this emulated with help of netlist, including the stupid production error in Philips 8250. =)

Re: ay8910 [Re: Dr.Venom] #92322 01/14/14 08:26 PM
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That would be super cool. Hopefully netlist will settle down into a production form soon; I'll take the appearance of a second TTL game driver (ie, not Pong) as meaning that's at least close ;-)

Re: ay8910 [Re: Dr.Venom] #92323 01/14/14 09:53 PM
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judge Offline
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And then we'd also have to really start cleaning up the msx driver code as well...

Re: ay8910 [Re: couriersud] #92333 01/15/14 01:50 PM
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Dr.Venom Offline OP
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Originally Posted By couriersud

Note that these schematics are for the Spectravideo 318/328, which is not officially an MSX machine (although very close). See here. The first Spectravideo MSX machine was the SVI-728, which also had a completely reworked mainboard.


Originally Posted By hap
Yeah, volume balance differs often between models. I'd love to see this emulated with help of netlist, including the stupid production error in Philips 8250. =)

Emulating the differences between models would bring forward the question what model / schematic the defaults "msx" , "msx2" and "msx2p" should be based upon?

Preferably (IMO) they would be based upon a model / schematic for which:
a) all components are known (no guessing of values), and
b) for which we have a real machine/model to verify the emulation results against

such that we obtain high / verified accuracy for the default drivers. I guess the NMS8245 matches these criteria, but I don't know if that's possible from a netlist viewpoint (with the high-pass filter in there and such).

Added bonus would be no DC offset :-)

Last edited by Dr.Venom; 01/15/14 01:53 PM.
Re: ay8910 [Re: Dr.Venom] #92334 01/15/14 06:38 PM
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IMO the defaults "msx" , "msx2" and "msx2p" should be removed from MESS =)

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