Author Topic: What is custom stereo Dac on mega everdrive x7?  (Read 3596 times)

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Offline Crimsonseraph188

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What is custom stereo Dac on mega everdrive x7?
« on: October 24, 2016, 09:12 PM »
As the title suggests, im confused about what custom stereo dac is since it is only included in the x7, vs the x5 and x3. Thanks!

Offline thecavalry

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #1 on: October 25, 2016, 10:50 PM »
Currently I think this feature is disabled in the latest OS revision. Krikzz may have to weigh in on that. Anyways, DAC is digital-to-a converter. It's on there because some model 2 motherboards have really bad sound handling compared to other board revisions.

From the mega everdrive manual:

Sound File Playback
The Mega EverDrive currently allows 8-bit 22Khz Stereo WAV file playback. The
(C) button allows user to switch between the internal Genesis DAC or Mega
EverDrive's internal stereo DAC.
Mega EverDrive's internal stereo DAC sounds terrible on Genesis Model 2 with
motherboard revision VA0-VA1.

Offline Arnold101

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #2 on: September 02, 2017, 10:54 PM »
Currently I think this feature is disabled in the latest OS revision. Krikzz may have to weigh in on that. Anyways, DAC is digital-to-a converter. It's on there because some model 2 motherboards have really bad sound handling compared to other board revisions.

From the mega everdrive manual:

Sound File Playback
The Mega EverDrive currently allows 8-bit 22Khz Stereo WAV file playback. The
(C) button allows user to switch between the internal Genesis DAC or Mega
EverDrive's internal stereo DAC.
Mega EverDrive's internal stereo DAC sounds terrible on Genesis Model 2 with
motherboard revision VA0-VA1.
so what as been disabled? changing dac with C not work for me. So now it use console dac to play wav? or cart one?

Offline Amerika

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #3 on: September 08, 2017, 09:29 AM »
I was not aware that this was a feature of the x7.  I own one and I also specifically got my hands on a model 1 "High Definition Graphics" Genesis to make sure that I had good sound.  But I do have a model 2 that would go better with my model 2 Sega CD and fit my shelving a lot easier if that DAC fixes the sound issues in those models.

So yeah, I would definitely like to know more about that feature, how it's enabled and if it's currently working or at least has a toggle in the latest OS release.

Thanks!!
NES Everdrive N8, SD2SNES, Mega EverDrive x7, Turbo EverDrive, NeoSD, EverDrive-GBA x5, Ultra EverDrive64 v3

Offline Ali-Pacha

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #4 on: December 15, 2018, 08:55 PM »
Just did some digging, but I didn't find any answers to some questions about this feature :
- which DAC is included within the Mega ED X7 ? Some Burr Brown / Texas Instrument / Cirrus Logic /Sabre "mainstream stuff" or something else ?
- what's exactly the function allowing streaming through the Megadrive audio circuitry ? Looks like there are dedicated pins on the cartridge slot (and those pins are disconnected on the Sega Nomad, seen a thread about this), but I don't fully understand why Sega did this...
- ...because obviously, no game did benefit from this feature back in the days. RAM-size issue ?
- and last but not least, why is it limited to 8-bit - 22 khz stereo ? Looks like it isn't a full "pass-thru" feature, but something that deals with some chips limitation within the Meagdrive. And it doesn't look like it has something to do with the YM2612, the DAC within is mono but can go up to 26 khz...

Last question : I've some "clicks" from time to time when playing a song through this feature (8 bit - 22 khz, directly ripped from CDs)...any idea where it comes from ?

I know it's only a proof of concept, but whenever Krikzz is around, I'd be glad to know more about this stuff :)

Ali

Offline DhinCardoso

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #5 on: January 11, 2019, 09:33 PM »
My Megadrive really sounds bad, I would love to know that if I can use the X7 to solve this or have I to mod it with MegaAmp or such =/

@KRIKzz ! Help us!

Offline DrYak

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Dac on mega everdrive x7
« Reply #6 on: February 07, 2019, 07:34 PM »
- which DAC is included within the Mega ED X7 ? Some Burr Brown / Texas Instrument / Cirrus Logic /Sabre "mainstream stuff" or something else ?

Less sure for that part, I don't own an x7 yet (waiting to set some budget aside for that), but from the picture I've seen, it seems that the audio pin are wired to the FPGA.
So, "something else", the audio seems to be generated as part of the circuitry simulated by the FPGA (same as the FM for old SMS games).

But we'll have to wait for Krikzz to chip in and tell how he's setup the audio.

- what's exactly the function allowing streaming through the Megadrive audio circuitry ? Looks like there are dedicated pins on the cartridge slot (and those pins are disconnected on the Sega Nomad, seen a thread about this), but I don't fully understand why Sega did this...
- ...because obviously, no game did benefit from this feature back in the days.

Actually, adding extra audio hardware has always been quite popular on several consoles. (Atari 7800 game carts could feature an extra Pokey for better audio, etc.)
SEGA's 8bit console have not been different from that point of view: some game could support an extra FM sound chip. Though in some later console versions (Japanese master system) the chip was built-in, it was initially an optional add-on thus the ports of the console (SG-3000) obviously need to carry audio (sadly, some later console like the western Master system dropped the option altogether and require soldering to re-enable).

So of course it would seem obvious to SEGA engineer to add extra pins for audio routing.

In the case of the mega drive :
 - the Sega CD uses the audio pins on the extension port to mix its audio (e.g.: for playing CD audio).
 - the 32x uses the audio pins on the cartridge port to mix its audio (extra PCM channels)
 - the SVP chip could add extra audio through the cartridge port.

And although not officially supported by SEGA in the Powerbase converter, there are solution to add the optionnal FM chip used in 8bit consoles and mix it through the cartridge port audio.
e.g.: the Mega Everdrive x7 can simulate a YM2413 core on its FPGA to add FM to supporting SMS games.

Another SEGA console example:
the Game Gear has audio pins which are used by the TV tunner to bring the audio in.

no game did benefit from this feature back in the days. RAM-size issue ?

RAM (if you decide to store actual samples) would be one reason, and the already decent-enough quality of the built-in FM Synth would be another (little incentive to add yet another synth).

e.g.: Virtua Racing doesn't actually use the audio capability that SVP could provide, because the cartridge is already expensive enough like this (with the SVP), no need to increase the price even more by adding more ROM just for extra samples.

On the other hand, the Sega CD did definitely not suffer from space limitation and some game take their music from the CD (and feed it through the external port).


Offline Marteicos

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Re: What is custom stereo Dac on mega everdrive x7?
« Reply #7 on: February 07, 2019, 07:55 PM »
The 32x cart port in have audio input pins, they are connected to its own mixer, the audio out from this mixer goes to the cartridge port to Mega Drive.