Analogue Audio

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witchmaster
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Analogue Audio

Postby witchmaster » Thu Oct 11, 2018 7:31 am

What can be expected from analogue audio output of the MISTer (using the IO board). Does all cores support it and how is the quality?

@Sorgelig wrote in the Genesis Core thread, and I quote: "analog audio may get interference from other components. Also DAC used on I/O board is primitive. So you may hear some side signals like on old computers where you could hear how HDD is working through speakers"

Are the "side signals" something I can expect or is the analogue audio with the DAC on the IO board usually OK? From the schematic of the IO board I can see that the DAC uses passive components only. I guess that the audio signal coming from GPIO1 pins 2 and 7 is PWM?

I would prefer to use analogue audio so I'm looking into the options:
1. Buy the IO board or build the DAC part of it only for my project.
2. Buy an HDMI audio extractor.
3. Build a more advanced DAC.

I'm going to experiment myself but I figured it's good to ask since others probably have experience with this already. Grateful for any input! :)

Sorgelig
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Re: Analogue Audio

Postby Sorgelig » Thu Oct 11, 2018 10:16 am

analog DAC is Sigma-Delta.
Quality is actually OK, because all these retro systems never had high quality audio, so it's not tainted by this DAC.
Another issue with analog audio is BOOM sound when you load the cores. Different cores have different zero level making the capacitor charge at some level and then discharge when other core is loaded.

Besides the analog audio and HDMI, there is an option to use I2S external DAC as it's used in my PiTop case schematic. I2S signals arae available on I/O board v5.5. So you can use the same I2S DAC. Note: there is no MCLK signal so you need to choose a correct I2S DAC.

Generally speaking, none of existing cores provide high quality audio, so there is no point in expensive DACs.

witchmaster
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Re: Analogue Audio

Postby witchmaster » Thu Oct 11, 2018 12:05 pm

Thank you very much for the clarification! :)

amadama
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Re: Analogue Audio

Postby amadama » Thu Oct 11, 2018 2:48 pm

Sorgelig obviously knows the most and has the definitive answer.
I will share what I'm doing, and it works well for me.
I use my MISTer connected to either CRT VGA monitor or 4:3 1600x1200 LCD.
I don't have the I/O board (only SDRAM).
I use an HDMI to VGA adapter that has an audio output:

https://www.amazon.com/gp/product/B00ZM ... UTF8&psc=1

Image
Image

Works great for me and it's cheap. (about US $8)
I also use it for Raspberry PI and other SBC. For MISTer no need to connect the USB power, just plug the VGA and audio and it just works.
If using a 4:3 monitor make sure all cores you are running are set to 16:9 aspect ratio so they fill the screen.
Good luck!

Sorgelig
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Re: Analogue Audio

Postby Sorgelig » Thu Oct 11, 2018 3:51 pm

amadama wrote:If using a 4:3 monitor make sure all cores you are running are set to 16:9 aspect ratio so they fill the screen.

for 4:3 monitors it's better to select 4:3 resolution in MiSTer.ini like 1024x768

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Re: Analogue Audio

Postby amadama » Thu Oct 11, 2018 6:13 pm

Thank you Sorgelig. That works very well indeed. Last time I tried it it did not work because I altered the wrong setting (I put the value in DVI mode line by mistake).

Is there a 1600x1200 mode (native resolution of my monitor)?

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Re: Analogue Audio

Postby BBond007 » Thu Oct 11, 2018 6:20 pm

witchmaster wrote:
I'm going to experiment myself but I figured it's good to ask since others probably have experience with this already. Grateful for any input! :)


I just built up the analog audio circuit from the IO board schematic on a bread board with through-hole components. It was maybe 6 or so caps and a few resistors. (pic here: viewtopic.php?f=117&t=33895)

I have the audio out of the monitor connected to a switch box.I honestly can't tell the difference between the HDMI audio and the analog. I notice no crosstalk or noise. I don't know if I should expect less or more noise how I did it.

The BOOM Sorgelig spoke of when changing cores definitely happens but does not bother me even though I have a subwoofer connected. To me its more of a POP than BOOM.

It's definitely not like the Raspberry Pi where the analog audio is totally popping and hissing garbage compared to the HDMI output. I ended up putting a HiFiberry on that thing.

Sorgelig
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Re: Analogue Audio

Postby Sorgelig » Thu Oct 11, 2018 6:53 pm

amadama wrote:Is there a 1600x1200 mode (native resolution of my monitor)?

there is no predefined 1600x1200 resolution but still can be created in ini as custom resolution. But it may not work due to high pixelclock frequency.
I suggest to use 800x600 which is exactly quarter of 1600x1200 and should look perfect.

witchmaster
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Re: Analogue Audio

Postby witchmaster » Fri Oct 12, 2018 7:18 am

amadama wrote:I use my MISTer connected to either CRT VGA monitor or 4:3 1600x1200 LCD.
I don't have the I/O board (only SDRAM).
I use an HDMI to VGA adapter that has an audio output:

Works great for me and it's cheap. (about US $8)
I also use it for Raspberry PI and other SBC. For MISTer no need to connect the USB power, just plug the VGA and audio and it just works.
If using a 4:3 monitor make sure all cores you are running are set to 16:9 aspect ratio so they fill the screen.
Good luck!

Thank you for that idea! A CRT monitor would be nice to use with the MISTer indeed but currently I don't have one.

BBond007 wrote:I just built up the analog audio circuit from the IO board schematic on a bread board with through-hole components. It was maybe 6 or so caps and a few resistors. (pic here: viewtopic.php?f=117&t=33895)

I have the audio out of the monitor connected to a switch box.I honestly can't tell the difference between the HDMI audio and the analog. I notice no crosstalk or noise. I don't know if I should expect less or more noise how I did it.

The BOOM Sorgelig spoke of when changing cores definitely happens but does not bother me even though I have a subwoofer connected. To me its more of a POP than BOOM.

It's definitely not like the Raspberry Pi where the analog audio is totally popping and hissing garbage compared to the HDMI output. I ended up putting a HiFiberry on that thing.

Thanks! I ended up doing the same yesterday. I get some slight noise/crosstalk but it's not too bad, it seems to be sporadic. I didn't notice any issues with the Amiga core but with the TurboGFX core I noticed some high pitched whining sound. At least so far I'm happy with the analogue audio quality. The POPs when changing cores doesn't bother me at all.

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Re: Analogue Audio

Postby Shamus » Mon Oct 15, 2018 3:16 pm

I also simply grabbed the analogue signals and ground from GPIO1. The resistors and caps fit on a tiny PCB, see schematic. The "crack" sound when switching to the OSD main menu is absolutely bearable. It actually never annoyed me before reading this forum thread.
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