Zemmix Neo BR Balanced Audio

By Parn

Champion (278)

Parn's picture

09-04-2018, 15:35

By now it is common knowledge that the Zemmix Neo is a great MSX machine, very compatible and feature complete, but it has a very noisy audio output. I have one of the Brazilian Zemmix Neos and this kinds of ruin the experience for me, so I got very excited when I heard KdL added support for balanced audio output to the OCM firmware.

I got myself a proper cable a couple months ago, but real life prevented me from testing it until yesterday. My Zemmix Neo had an old firmware, so I proceeded to install the most recent one (3.5). I was a bit afraid of bricking it, but the process couldn't go more smoothly.

As soon as I sent the proper smart command, I was surprised to see most of the noise was gone. But, and this is a big but, there was still noise. It got much better, but it was still bad, so I was kind of disappointed, despite my initial surprise. I tried a few VGM files, but then I decided to try the Xak 3 set.

Then I noticed the FM/PSG balance was borked. I'm not 100% sure about this (should have made some recordings for comparison purposes), but I really don't remember the PSG being so much louder than the FM. I reduced the PSG to level 3/7 and it still seemed a bit too loud, but 2/7 made it almost inaudible, so I stayed with 3/7. As soon as I can I'll test it further, and throw the SCC in the mix to see how it goes.

I wonder if anyone had the same issues, and whether it is something related to the new firmware or the balanced audio.

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By Meits

Scribe (4962)

Meits's picture

09-04-2018, 18:03

There's no way to get balanced output from an MSX unless it gets physically built in. The RCA connectors only have 2 lines while balanced needs 3 lines. Balanced output/input only prevents interferance to be picked up by the cable.
Noise already present in the audio before going into the balanced cable will remain. The noise in the audio is picked up on its way to the RCA connector since the audio rail is one big antenna screaming for interferance. You probably got a high quality shielded RCA cable in stead. This is still unbalanced, but does a descent job in keeping interferance away.

Volume balancing between the several sound chips is the only thing you can do when it comes to the term balance. Firmware can boost volumes.

By Parn

Champion (278)

Parn's picture

09-04-2018, 19:11

I didn't expect the noise to completely go away, but I was still disappointed at the remaining noise. I thought the idea of inverting the waveform on the right audio output was very clever and had high hopes for the results. It really worked, just not as well as I wanted.

Of course, the cable I used is not a full balanced cable since the Zemmix Neo doesn't have a balanced audio connector. It's actually a good stereo cable with a balanced connector in one end. But I forgot to report something else: after setting the feature on, video quality on the RGB output became noticeably worse. It looked like jailbars, but with waving on the edges. The problem went away when I turned the inverted audio feature off.

Clearly the Zemmix Neo's analog output circuit leaves much to be desired. I'm just curious if I'm the only one to experience these issues.

By KdL

Paragon (1078)

KdL's picture

19-04-2018, 02:25

This situation has just been improved...
https://twitter.com/ocm_pld_news/status/986760038663454720

By Parn

Champion (278)

Parn's picture

19-04-2018, 15:00

Great news, KdL! You rock! Big smile

By raymond

Champion (315)

raymond's picture

19-04-2018, 17:30

Ah, sounds like a great update Big smile

By Pencioner

Hero (559)

Pencioner's picture

19-04-2018, 22:02

Thanks!
Soooo i wanted to have a look at it but https://gnogni.altervista.org/ shows me some parking page instead :)

By KdL

Paragon (1078)

KdL's picture

20-04-2018, 11:02

It will be available soon...

My MSX profile