VDP Noise

By Meits

Scribe (4331)

Meits's picture

11-08-2017, 22:36

This well known (and in this case amplified) noise is what I really do not like on MSX. It's always there. No matter what.
To avoid as much as possible interferance I cut pin 49 on all my sound cartridges (I never use my monitor's speakers). Still it's there. One cartridge suffers more than the other. You'd expect cartridges with jack connectors to not sends the noise from the MSX itself to the amplifier, but both the pin 49 cut cartridges and the jack cartridges still carry a lot of very unwanted noise to the amplifier.
Is there really no way to keep the MSX's ugly noise completely outside the audio signal? Sure, once something's playing you don't hear it, but there's not always something playing. It just has to be gone... Forever...

Any solutions?

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By Louthrax

Paragon (1518)

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11-08-2017, 23:22

It depends on the machines... On my VG-8235, that parasite noise is very low. In order to minimze the noise, I'm using short SCART cables up to a SCART multiplexer, which has its own audio output (that goes to amplifier). From my understanding, long or badly isolated video & audio cables seem to amplify intereferences by induction (or something)...

A bit surprising you are also experiencing those noises with direct cartridges jack connectors... Some external devices like MFR SCC tend to produce parasites, but mainly when they are accessing the SD Card.

On SCART output, the noise is more audible on turboR where the average output volume is lower, when the parasites still have the same volume.

I have no good solution for that.... Adding capacitors or filters, or using an equalizer, will have a bad impact on the "real" sounds. Solution should be probably found before the output?

Also, if that can make you happier, I have lots of other gaming systems here (NES, SNES, MegaDrive, PC Engine, etc...), and all of them have some background noises just like on MSX.

By Manuel

Ascended (13299)

Manuel's picture

11-08-2017, 23:25

By Meits

Scribe (4331)

Meits's picture

11-08-2017, 23:34

It's an ST with in slot 1 a mfrscc+sd2 with custom jack. Cut off from MSX when jack inserted. Noise.
In slot 2 an Gouda 5.0 slotexpander with any moonsound clone you can imagine (all jack, all noise), a Philips Music Module with pin 49 cut (noise) and an FM-PAQ lite (jack but low on noise).
Everything goes through absolutely high quality expensive pro cables to several mixers which remove ground-loop with use of balanced cables. One of the mixers equalizes high, low and mid tone.
I can lower the volumes so the VU meters hardly react and put my headphones louder. This makes it quite well listenable, but if I want to record I've to put the mixers louder to get around 0dB. The VDP noise adores this cuz it can creep to the foreground again.
Can't say I agree on that.

By Meits

Scribe (4331)

Meits's picture

11-08-2017, 23:55

Manuel wrote:

It has some good sides: https://www.youtube.com/watch?v=rGA_fVegAb4

Nice trick, but if it would mean that this clip could never exist, I'd be quite happy...
I have a *cough* Amiga here (in store, so at ease :D ) which produces nothing like this from the internal soundprocessor, while here it even comes from external sound chips which have their audio line to the noise source cut off completely. Still I hear what happens on screen. O_o

By Grauw

Enlighted (5822)

Grauw's picture

12-08-2017, 00:19

Easy fix: COLOR 0,0,0

VGMPlay has a /B option which does this.

To still see something while minimising the noise, use COLOR 15,0,0 : COLOR=(15, 0, 1, 0).

By sd_snatcher

Prophet (2439)

sd_snatcher's picture

12-08-2017, 02:45

@Meits

As the video that Manuel link pointed out, the 60Hz clicking noise is caused by the VBLANK. It might contaminate the audio line via a number of reasons:

1) Contamination from the VDP SYNC lines (the most frequent case), see (3)
2) Contamination from the Z80 /INT line see (3)
3) Poorly designed motherboard: mix of analog/digital areas, poor Vcc filtering, poor/inexistent ground plane
4) When cartridges still have that noise after you have cut their sound line to the MSX, this means that they have poor filtering on the Vcc and probably poor or inexistent ground planes
5) CXA1145 TV-Encoder: This little chip was revolutionary its time, and offered amazing video cost/benefit for the time. Just compare the video output from the HB-F1mk2 versus the HB-F1 to see how much the image quality has improved.

That said, the CXA1145 is now an old chip with a lot of shortcomings. The most relevant are:

- Prone to produce jailbars on video if the circuit wasn't very carefully designed
- The integrated audio buffer has a tendency to contaminate the audio with the vertical sync. This is why they removed the audio buffer for the subsequent generations of the chip: CXA1645 and CXA2075.

That said, there are well designed machines where there are no jailbars and the vertical sync is way less noticeable. The most notable examples are the Sony HB-F1mkII and Sony MSX2+ models.

The Sanyo MSX2+ machines get way better in this department after this audio fix. Not perfect, but the SNR is noticeably better.

By Meits

Scribe (4331)

Meits's picture

12-08-2017, 12:49

Good to know that I have a Sony HB-F1DXJ (being repaired now).
It would be great it there's a line from the computer to the cartridge which could be cut to keep this critter away from the audio without cancelling the function of the cartridge. I remember my Philips Music Module became a lot cleaner when I cut pin 49, but it wasn't clean yet. Yes, I accept constant low volume noise which is almost always present in analog audio, but noise of sd card access and vdp actions should stay away from audio lines which are far away from the mainboard in cartridges with jack plugs or cut pin 49.

Grouw: that doesn't help in this case. color 15 and color 0 generate the same noise at the same volume.

By Grauw

Enlighted (5822)

Grauw's picture

12-08-2017, 14:04

It depends on the machine and connection whether COLOR will work, but on all of mine (turboR GT, CX5MII and Zemmix Neo) it makes quite a difference. If the noise changes colour when the screen content changes (a familiar sound for most I think), that’s a good indication that COLOR 0,0,0 will reduce the noise.

By Meits

Scribe (4331)

Meits's picture

12-08-2017, 15:55

But isn't that only when you grab the audio straight from the machine itself?

My MSX profile