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 Post subject: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 3:49 am 


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So, I've seen random mentions of the N64 being capable of native digital audio but I can't seem to find any actual guides/mods/PCBs for how to actually do it. Is this really possible? I'd assume it is since the UltraHDMI mod exists, unless that's just taking the analog audio and converting it to digital.
I just want a way to be able to send digital audio to a receiver or something while sending RGB to a CRT or OSSC. Bonus points if it works with already existing boards such as the SNES digital audio mod.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 7:38 am 


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N64 audio is all over the place internally, different frequencies in different games and stuff, apparently it took Marshall a very long time to get the analogue to digital audio working on the UltraHDMI so I doubt a SPDIF mod would be straightforward.
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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 1:26 pm 


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BuckoA51 wrote:
N64 audio is all over the place internally, different frequencies in different games and stuff, apparently it took Marshall a very long time to get the analogue to digital audio working on the UltraHDMI so I doubt a SPDIF mod would be straightforward.


Oh, so it's confirmed the UltraHDMI mod takes the analog audio and converts it to digital? I was just assuming it was tapping digital audio signals like the SNES SPDIF mod does. When using RGB I only care about a digital audio mod that's digital to digital since analog to digital isn't going to perform any magic unless someone just had bad quality cables.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 1:46 pm 


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cr4zymanz0r wrote:
BuckoA51 wrote:
N64 audio is all over the place internally, different frequencies in different games and stuff, apparently it took Marshall a very long time to get the analogue to digital audio working on the UltraHDMI so I doubt a SPDIF mod would be straightforward.


Oh, so it's confirmed the UltraHDMI mod takes the analog audio and converts it to digital? I was just assuming it was tapping digital audio signals like the SNES SPDIF mod does. When using RGB I only care about a digital audio mod that's digital to digital since analog to digital isn't going to perform any magic unless someone just had bad quality cables.


No marhall's mod uses the digital audio signals. The audio DAC itself is somewhat weird and does not use a master clock and there lies the problem for an audio mod, and trying to stop jitter. I've thought about trying L-Trains SNES mod, as I think it will work fine. Just haven't had the time.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 6:32 pm 


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citrus3000psi wrote:
No marhall's mod uses the digital audio signals. The audio DAC itself is somewhat weird and does not use a master clock and there lies the problem for an audio mod, and trying to stop jitter. I've thought about trying L-Trains SNES mod, as I think it will work fine. Just haven't had the time.


Let me know if you get time and make some progress. I ordered some of your PCBs off Oshpark and will be Toslink modding all my compatible consoles in the coming weeks :)


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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 8:15 pm 


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cr4zymanz0r wrote:
citrus3000psi wrote:
No marhall's mod uses the digital audio signals. The audio DAC itself is somewhat weird and does not use a master clock and there lies the problem for an audio mod, and trying to stop jitter. I've thought about trying L-Trains SNES mod, as I think it will work fine. Just haven't had the time.


Let me know if you get time and make some progress. I ordered some of your PCBs off Oshpark and will be Toslink modding all my compatible consoles in the coming weeks :)


Im not sure when I'll get the time, as I'm juggling too many projects right now. However I think I read borti might be investigating it. :D


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 Post subject: Re: N64 digital audio mod?
PostPosted: Mon Mar 26, 2018 9:22 pm 



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Posts: 1348
Is the digital audio offered by the Ultra HDMI a noticeable improvement over the standard analog audio? Or is it just simply for convenience and compatibility sake?


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 Post subject: Re: N64 digital audio mod?
PostPosted: Tue Mar 27, 2018 4:00 am 



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GeneraLight wrote:
Is the digital audio offered by the Ultra HDMI a noticeable improvement over the standard analog audio? Or is it just simply for convenience and compatibility sake?

As with other native-digital audio solutions, you won't have issues with interference/crosstalk or an analog noise floor. If you have any hiss from your N64 using the analog audio, it will disappear when you switch to digital. This was the case with my Xbox, when I switched from the analog RCA audio to TOSLINK--no more hiss--the silence was actually silent.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Tue Mar 27, 2018 12:33 pm 


citrus3000psi wrote:
However I think I read borti might be investigating it.


You are right here. The "problem" is that the master clock is not present on the N64 mainboard (at least I haven't found it). This however can be recovered from left/right clock using a PLL. To keep the mod easy a stand-alone specialized one would be preferable; but I haven't found one yet.
Nevertheless, the CS4350 audio DAC has an internal PLL doin' that task. I'm thinking of just using this IC to recover master clock and leaving the analog part unused, here. Then one would have the master clock available for the SPDIF transmitter.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Tue Mar 27, 2018 3:22 pm 


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borti4938 wrote:

You are right here. The "problem" is that the master clock is not present on the N64 mainboard (at least I haven't found it). This however can be recovered from left/right clock using a PLL. To keep the mod easy a stand-alone specialized one would be preferable; but I haven't found one yet.
Nevertheless, the CS4350 audio DAC has an internal PLL doin' that task. I'm thinking of just using this IC to recover master clock and leaving the analog part unused, here. Then one would have the master clock available for the SPDIF transmitter.


Thats a cool IC. 8) Didn't know there was such a thing. I'm going to have to squeeze toslink some how on my machine now :wink:


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 3:19 am 



Joined: 11 Jun 2014
Posts: 15
I got a hold of an N64 to try my SNES SPDIF mod on, and as I suspected, it works! I'm not sure if it's 100% compatible with the N64 since I only have one game (Super Smash Bros.), but this is very promising.

Spoiler: show
Image


For those that are willing to experiment and try this out, boards and info are here: https://oshpark.com/shared_projects/5NrKCmY9. I tapped the I2S signal from the DAC, the reset signal comes from pin 6 on the PIF-NUS (the /ColdReset pin), and 5V is sourced from the onboard regulator.

I'd like to get my hands on some more games to test with. Does anyone know of any games that have very low (e.g. 22050 Hz) or non-standard playback rates? Or if there are any games dynamically change their playback rate during game play?


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 12:30 pm 


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L-Train wrote:
I got a hold of an N64 to try my SNES SPDIF mod on, and as I suspected, it works! I'm not sure if it's 100% compatible with the N64 since I only have one game (Super Smash Bros.), but this is very promising.

Spoiler: show
Image


For those that are willing to experiment and try this out, boards and info are here: https://oshpark.com/shared_projects/5NrKCmY9. I tapped the I2S signal from the DAC, the reset signal comes from pin 6 on the PIF-NUS (the /ColdReset pin), and 5V is sourced from the onboard regulator.

I'd like to get my hands on some more games to test with. Does anyone know of any games that have very low (e.g. 22050 Hz) or non-standard playback rates? Or if there are any games dynamically change their playback rate during game play?



Great news :D , I had a feeling your board would work.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 3:05 pm 


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L-Train wrote:
I'd like to get my hands on some more games to test with. Does anyone know of any games that have very low (e.g. 22050 Hz) or non-standard playback rates? Or if there are any games dynamically change their playback rate during game play?

I'm not knowledgeable about the technical side of digital audio, but are you expecting potential problems or just covering your bases? I really don't want to do all that surface mount soldering on that board only to find out there's issues with some games and have to do it all over again later after a board revision :P


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 4:49 pm 


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cr4zymanz0r wrote:
L-Train wrote:
I'd like to get my hands on some more games to test with. Does anyone know of any games that have very low (e.g. 22050 Hz) or non-standard playback rates? Or if there are any games dynamically change their playback rate during game play?

I'm not knowledgeable about the technical side of digital audio, but are you expecting potential problems or just covering your bases? I really don't want to do all that surface mount soldering on that board only to find out there's issues with some games and have to do it all over again later after a board revision :P

certain audio receivers are particular about sample rates on toslink... and the SNES is notorious for using odd ones, so I assume the thinking is the n64 would be similar


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 5:49 pm 



Joined: 11 Jun 2014
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cr4zymanz0r wrote:
I'm not knowledgeable about the technical side of digital audio, but are you expecting potential problems or just covering your bases?


A little bit of both. I don't expect problems with games that use a constant playback rate regardless if it's low or non-standard, but I'd still like to try them out. If the rate suddenly changes during game play however, the circuit is configured such that the SRC4192 should mute the output until it can determine the input/output frequency ratio. If it doesn't lock quickly enough we might get a bit of lost audio. That's just me speculating, I don't know if it'll actually behave that way.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Thu Apr 19, 2018 5:54 pm 


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Location: Indiana
Hey L-Train, you have an atari jag laying around. Wonder if your board works in that too.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Fri Apr 20, 2018 1:17 am 



Joined: 11 Jun 2014
Posts: 15
Unfortunately it looks like the Jaguar uses the I2S format while my board is hardwired for 16-bit right justified input, and it also has a muting signal since it can output non-audio data over that serial bus, so it can't be used without a few small changes to the circuit.

Edit: Seems muting is already handled in the Jaguar so that's a non-issue, so it should work by tapping the I2S signal from the TDA1545, changing the input format on the SNES SPDIF board by lifting the IFMT0 and IFMT2 pins on the SRC4192 and connecting IFMT0 to VCC (3.3V) and IFMT2 to ground, and connecting /RST to pin 29 on the Jerry chip (XRESETL).


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 Post subject: Re: N64 digital audio mod?
PostPosted: Sat Apr 21, 2018 3:55 am 


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Just to add my own experience, the UltraHDMI is definitely an improvement over the standard analog audio output. I used it to rip the Doom 64 soundtrack, and it ended up being CLEANER than Aubrey Hodges's own OST (his is riddled with 60 cycle hum).
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 Post subject: Re: N64 digital audio mod?
PostPosted: Sat May 23, 2020 1:44 am 


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So have there been any more advancements in N64 digital audio mods? I ordered L-Train's PCB from oshpark forever ago but never got around to ordering the components.
I was thinking about revisiting it but was curious if there are better solutions now and/or if anyone else has tried L-Train's board on N64 without any issues.


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 Post subject: Re: N64 digital audio mod?
PostPosted: Sat May 23, 2020 4:01 am 



Joined: 11 Jun 2014
Posts: 15
Hey cr4zymanz0r, just wanted to let you know that I have a new version of the board nearly ready to go that adds a few features (jumper selectable input format, left/right channel swap, and on-the-fly switchable 48/96/192 kHz output). I'm currently waiting for the final boards from OSH Park and will create a new thread detailing it.

In terms of N64 compatibility, unmaker built up a prototype of the new board and noted that borti's flex cable (https://www.retrorgb.com/bortis-n64-fle ... pdate.html) is necessary to avoid occasional drop outs. You will also need it use it if you decide to build the old board.


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