DW8000 Hum/Noise - Just Normal Aliasing?

[grumphh]

I have never noticed any noise (unwanted, that is) coming from mine.

[Synth80s]

Thanks for the response. Just to clarify, are you talking steady state noise or have you ever tried what I described?

If you have any opportunity to confirm that your DW doesn't have any such issue, that would be very helpful: volume up, filter open, resonance at zero, play some very high notes and see if any low level hum seeps through when the amplitude envelope is open (the noise isn't terribly loud, but it's there under these conditions).

[grumphh]

Originally Posted by Synth80s

Thanks for the response. Just to clarify, are you talking steady state noise or have you ever tried what I described?

If you have any opportunity to confirm that your DW doesn't have any such issue, that would be very helpful: volume up, filter open, resonance at zero, play some very high notes and see if any low level hum seeps through when the amplitude envelope is open (the noise isn't terribly loud, but it's there under these conditions).

I just played it to see wether i have that - oscillators to 4' and playing in the upper octave and applying the pitchbender for another octave , filter open, no res amp sustain at max and trying with both saw and sine waves.
Painfully high, but no static (as in not-moving) hum or noise i could hear.

With the saw wave i got some (very low volume) aliasing, but it was only audible at high volume and only when using the pitchbender, where i got a sort of computerized background warble underneath the high shrieks.

Otherwise it is blissfully silent.

[m.o]

Is it the same on all outputs? (Or just on headphones or main out)

[cdog]

No Ive never experienced that. Im fairly picky about noise/hum and I do use headphones a lot so I think I would pick up on this. Even really low level ground loops or hum bug the shit out of me, although I dont have a ton of hours on my DW8000 and it isnt hooked up right now so I cant confirm 100%.

[xanderbeanz]

Yeah mine hums a bit, a bit noticeable when playing very high notes, but majorly noticeable in patches that use it's white noise.

[Synth80s]

Originally Posted by grumphh

I just played it to see wether i have that - oscillators to 4' and playing in the upper octave and applying the pitchbender for another octave , filter open, no res amp sustain at max and trying with both saw and sine waves.
Painfully high, but no static (as in not-moving) hum or noise i could hear.

With the saw wave i got some (very low volume) aliasing, but it was only audible at high volume and only when using the pitchbender, where i got a sort of computerized background warble underneath the high shrieks.

Otherwise it is blissfully silent.

Thanks -- this is very helpful info. I am planning to take it to a local tech for a preemptive battery replacement anyhow, so I can have him take a look.

[Synth80s]

Originally Posted by m.o

Is it the same on all outputs? (Or just on headphones or main out)

Good question -- I'll test tonight.

[Synth80s]

Originally Posted by xanderbeanz

Yeah mine hums a bit, a bit noticeable when playing very high notes, but majorly noticeable in patches that use it's white noise.

OK, that's exactly what I'm experiencing. So the question remains: is it somewhat normal or do we have a common issue? Hmmm....

[stalker]

Originally Posted by xanderbeanz

Yeah mine hums a bit, a bit noticeable when playing very high notes, but majorly noticeable in patches that use it's white noise.

Mine behaves the same way..

[Synth80s]

Originally Posted by cdog

No Ive never experienced that. Im fairly picky about noise/hum and I do use headphones a lot so I think I would pick up on this. Even really low level ground loops or hum bug the shit out of me, although I dont have a ton of hours on my DW8000 and it isnt hooked up right now so I cant confirm 100%.

Thanks for the reply. If you happen to have your DW8000 powered up anytime in the near future, try it with the main outputs. I will try mine with the headphone outputs and report back.

[Synth80s]

For the record, I'm not trying to scare anyone away from the DW8000 or blow this issue out of proportion. I know how threads like this can turn into future references like "the DW8000 has a big hum/noise problem." That's not the case! I'm just curious, as always, and looking for an answer.

The hum on my unit is not terribly loud, so it's only noticeable when the DW is playing high notes in isolation at high volume (like C5 and up). It's masked at all other times -- lower notes played and/or in a mix. And as others have mentioned, it's most noticeable when using the noise generator -- that might be a clue that it's just aliasing or some other artifact considering how much quantization error there must be with the 8-bit waveforms (I'm assuming the noise generator is a sample as well).

I'll give this thread time to pickup some additional responses from DW/EX owners, but I'm starting to think this is just normal. Or since all of our DWs are 100 years old, maybe they're all developing the same issue to some degree.

If any Korg-savvy techs are reading this, feel free to chime in with ideas/opinions. Thanks!

[lilita]

Mine has a horrible hum but it's coming from the effects unit. Turn off effects (a shame) and it all goes away

[acreil]

Originally Posted by Synth80s

And as others have mentioned, it's most noticeable when using the noise generator -- that might be a clue that it's just aliasing or some other artifact considering how much quantization error there must be with the 8-bit waveforms (I'm assuming the noise generator is a sample as well).

8 bits is adequate for representing a single cycle waveform at full amplitude. And Korg used some conservatively band limited and oversampled wavetables (which are actually huge compared to most similar synths), so aliasing isn't a big problem. The noise source is analog.

I'm guessing you're getting some cross-talk from either the multiplexed control voltage circuits, or the circuits that scan the front panel buttons and keyboard. It could be coming through the power, or some poorly arranged wires.

[Synth80s]

Originally Posted by acreil

8 bits is adequate for representing a single cycle waveform at full amplitude. And Korg used some conservatively band limited and oversampled wavetables (which are actually huge compared to most similar synths), so aliasing isn't a big problem. The noise source is analog.

I'm guessing you're getting some cross-talk from either the multiplexed control voltage circuits, or the circuits that scan the front panel buttons and keyboard. It could be coming through the power, or some poorly arranged wires.

Thanks for all the valuable information -- very interesting stuff.

In your opinion, would the cross-talk represent a design issue that would potentially affect all units (assuming there were no factory revisions to address it) or do you think it's that possible wires in some units have moved around where they shouldn't be? I've certainly seen plastic cable clips/organizers fail inside PCs which allowed cables to move about and cause issues.

Also, does the fact that the hum is loudest when the noise generator is invoked suggest anything specific about its source?

Thanks again,
Synth80s

[wooster]

do consider that audio paths that have capacitors in line will dry out over time, as all audio gear,....so that could be a source for noise issues

[acreil]

Originally Posted by Synth80s

In your opinion, would the cross-talk represent a design issue that would potentially affect all units (assuming there were no factory revisions to address it) or do you think it's that possible wires in some units have moved around where they shouldn't be? I've certainly seen plastic cable clips/organizers fail inside PCs which allowed cables to move about and cause issues.

I don't remember exactly how the wires are arranged inside it, or what circuits are on what board. The thing is that the wires connecting to the keyboard and front panel are radiating high frequency energy that can couple into other signals if they're too close. I've had problems before with mis-routed ribbon cables when assembling something, resulting in increased noise. Or it could be the main power supply capacitors or local decoupling capacitors. An oscilloscope would help a lot.

Also, does the fact that the hum is loudest when the noise generator is invoked suggest anything specific about its source?

There's a lot of gain in the noise circuit. Any interference that gets into that part of the circuit will be amplified more than interference received by other circuits.

[Gazdatronik]

Mine also does this. I have had two and they both did have this noise(which i thought was either 50 or 100 hertz), noticeable CONSTANTLY! no matter what. It goes away when the filter is closed, so it is before that stage. I should look through the schematic and see any clock rates match, or maybe experiment with taking it apart and moving boards physically apart from one another. Maybe adding another prong on the plug and grounding the chassis.

If my luck is as bad as it is with synth designs, it will be in the mix amp!

[Gazdatronik]

http://www.pallium.com/bryan/dw/DW-8...ice_Manual.pdf

Here is the schematic/adjustment procedure, etc, for any who wishes to take a look along with me. I need to go in there and crank down the noise anyway, I never use it..

[Synth80s]

I'm taking my DW8000 to a local tech to have the battery replaced and socketed. I will describe the issue to him and see if he thinks there's a likely answer. While he's in there, I may also have him replace some old power supply caps for good measure.

[waveform:blue]

I had a similar problem with my Kawai K1r. While it has no filters, it does have ADSR envelopes. A light 120 Hertz hum would appear every time an envelope was open. The hum would also modulate some patches to produce a grainy "aliased" sound.

The fix was simple - a new in-line power supply.

I don't know a thing about the DW8000. However, I agree with acreil that the power supply is suspect. It could be time to replace some capacitors. If they are failing, you'll wind up with a 120 Hertz hum (North America and Japan) or 100 Hertz (just about everywhere else).

[Synth80s]

Originally Posted by waveform:blue

I had a similar problem with my Kawai K1r. While it has no filters, it does have ADSR envelopes. A light 120 Hertz hum would appear every time an envelope was open. The hum would also modulate some patches to produce a grainy "aliased" sound.

The fix was simple - a new in-line power supply.

I don't know a thing about the DW8000. However, I agree with acreil that the power supply is suspect. It could be time to replace some capacitors. If they are failing, you'll wind up with a 120 Hertz hum (North America and Japan) or 100 Hertz (just about everywhere else).

More good info, thanks.

Since the power supply on the DW8000 is obviously internal, I will ask my tech about rebuilding it as necessary. I found this synth at a good price and it's in near mint condition, so it's worthy of some tech love. When paired with the Kiwi Patch Editor, it's a lot of fun (especially the nutty delay).

[Gazdatronik]

I wish it were the power supply, but I know it isn't, at least in my case as I am in America. I can rebuild those with my eyes shut at this point, but I have the feeling that our noise in question may well be an "acceptable" flaw that came with the price point of the synth. I do have some hope that I will be able to isolate it and decouple it with a capacitor. If its as lazy as turning down the noise pot, I may do that and be over with it. Now that I am home from work, I can start on it.

[Gazdatronik]

Okay, I have figured it out. Its the LED display. Its refresh rate, is approximately 150hz. You win the prize! Got closer than I did. LED's are very noisy.

Well, from here it should be easy to fix. I may install a switch to kill the display entirely for when I'm not making edits. Should be easy enough to test that hypothesis

[grumphh]

Originally Posted by Gazdatronik

an "acceptable" flaw that came with the price point of the synth.

As the self-proclaimed valiant defender of the DW8000's honour i have to step in here.

It actually wasn't a budget synth when it came out (although it certainly wasn't in the unobtainable flagship price league either), and some of ours actually still perform noiselessly after appr. 30 years of use...

And it sounds a lot better than one would think, considering the sound quality (or rather lack thereof) that 150 - 200$ normally can buy you on the used market.

[Gazdatronik]

Okay. Tested and confirmed. Connector 9A(Digital board) is either the power or ground for the LED's, I unplug it and the noise goes away.

[Synth80s]

Originally Posted by Gazdatronik

Okay. Tested and confirmed. Connector 9A(Digital board) is either the power or ground for the LED's, I unplug it and the noise goes away.

Yep, I think you nailed it -- you are the man!

I already had the main screws out of my unit to check the battery, so I decided to unplug 9A and that basically resolved the low hum that's sometimes heard when the amplitude and filter envelopes are open. I A/B'd it a few times to be sure. With 9A disconnected, there are still some oddball aliasing noises coming through when high notes are played, but I'm certain those are digital artifacts from the synthesis engine as they change in frequency and amplitude based on the note(s) selected.

More confirmation: when 9A was re-connected and I held down a high note and modified a parameter that should otherwise have no effect on the sound, I can hear various noise in the audio path that corresponds directly with the the changing of the green parameter value LCD.

So the follow-up question: is this a design issue or an aged component(s) failing to isolate the display screen noise as designed? I'm guessing the former, but if you think of an easy fix, let me know -- I'm taking my unit into the tech on Thursday to have the battery replaced and socketed, so I'm open to ideas.

Once again, thanks for all your efforts Gazdatronik and others. It's threads like these that remind me of the mighty power of the internet community.

[Gazdatronik]

It is entirely possible that a lot of tiny capacitors, about 5 or 10 mfd coming off of each led segment could clear up the noise, but what I have decided to do is get an eight or ten pole single pole switch for an led kill. the caps may not be enough.

[grumphh]

Originally Posted by Synth80s

So the follow-up question: is this a design issue or an aged component(s) failing to isolate the display screen noise as designed?

A few of us do not have that particular noise. (And i did also test wether changing parameters made noises that shouldn't be there after reading about it).

Personally i very much doubt that Korgs engineers were so bad at designing circuits as to allow interference from a display to be audible in a new synth.

I'd blame 25+ years of age...