Any activity of the computer such as whirring drive makes it worse.

That is certainly characteristic of the effect I referred to, digital noise from operations within the laptop - screen updates and drive activity are common ones.

Since the digital noise gets into the audio circuitry at least partially via the ground tracks connecting between audio components on the circuit board, the same thing that affects hum pickup from a ground loop (a common earth path) also affects injection of digital noise into the signal path.

Being able to hear a recording of the sound can be very helpful for a technician, often once you actually hear it you can suggest fairly confidently what is causing it.

Trying an external USB interface moves the audio circuitry out of the laptop and away from the source of the digital noise, so if that is where it's coming from, the external unit should be free of the buzzing. Even a simple device like a Behringer UCA222 could work as a test, or better would be something like a Steinberg UR12 or Scarlett Solo. Connecting a device like this to a USB outlet on the laptop and choosing it as the audio output device eliminates the analog audio circuitry in the laptop.

Being able to use a dedicated line output rather than a headphone output is better also.

It would be good to be able to hear a recording to gauge the nature of the buzzing you're getting. Some of the things you've said leads me to suspect you're maybe not describing the usual hum/buzz heard with a ground loop, but rather some digital noise from other functions such as the laptop screen being injected into the audio circuitry. How this is heard can change with different plug configurations as this changes the path of electrical currents through the circuit boards in both the laptop and the keyboard.

I get this effect myself at times in my music monitoring via my KRK powered monitors. It's a bit annoying that it's there, but as it is only the monitoring that has that effect at times, I haven't worried about going through, diagnosing and changing the existing layout to reduce or eliminate it.

Thanks for all your input.  I will try to record.  But this buzzing is loud as heck and sounds like a ground loop buzz (based on my limited knowledge from listening to ground loop buzzes on youtube! and the fact that it is virtually eliminated by a ground buzz eliminator makes me suspect that as well.  Oddly, it does not require the laptop to be plugged in to an outlet --- battery does it as well.  Any activity of the computer such as whirring drive makes it worse.  But only marginally.  Man, this is frustrating!

Eli26 wrote:

levinite wrote:

I did misinterpret what you said. But it is still not clear what the situation is. Platypus gave a procedure to try to isolate the problem, but your answers are not clear at least to me.

First, disconnect the midi cable completely and connect only your Kindle (battery only), do you still get the hum? Does moving, jiggling or touching the cable make any difference? How loud is the hum in this case?

some more info: With MIDI not plugged in at all, and just the audio cable, there seems to be small amount of background hissing when computer audio is playing through the speakers.  It can be minimized by lowering the DP volume as I raise the computer volume to compensate for that.

When I then plug in USB cable to bring midi data to the laptop, at first I hear som ehigh pitched whiny noises and then steady buzz.  The buzz seems to be from 6-14 seconds at a time, with breaks of several seconds.  (This is largely eliminated when I use the mpow noise eliminator. )

Even with the noise eliminator to get rid of the buzzing, there is still a small amount of background hiss when audio is played and for several seconds later.

Some hiss from a computers headphone jack is not unexpected.
If you really want help you should follow the outlines given. It doesn't help to guess how you have everything set up.

OK, I certainly do really want help, so please forgive me if I was unclear.  I think I did follow the outline given.  How I have everything setup?  Casio GP 400 piano, USB cable (the printer kind) to the laptop, line out from headphone jack of laptop to the stero line in jacks in the casio gp 400.  Definite loud buzzing if I don't use a buzz eliminator downstream from the headphone output on my laptop.  And even with that, some background hiss, which I can reduce if the piano volume is lower, but that requires raising the computer volume quite high , which I think increases clipping.
With regards to the posted platypus procedural protocol....  I've embedded my answers below:

A process of elimination is usually needed to work out ground loop/hum problems. If I was trying to diagnose, I would first double check the audio cable itself is OK, simply plug the cable alone into the line inputs of the Casio. Because it's just an open cable, you could get a small amount of hum/noise, but if you hear as much hum with nothing connected as you get when it's connected, the cable itself may be the problem. If it's fairly quiet, move on

         OK I've moved on, because it seems to be fairly quiet unless I touch the cable or it touches another cable.

Next determine whether the hum/buzz is present without the MIDI connection, i.e. just using the Casio as an amplifier for the laptop sound output. You can of course test by just having them connected together, with the laptop running on battery. There should be no significant sound evident, until the laptop plays a sound source, e.g. music track or Pianoteq triggered from the integral mouse keyboard....

          Without the buzz eliminator, it buzzes. A lot.  (With the buzz eliminator, I get some background hissing when pianoteq or any other source produces sounds.  It
          makes it sound more artificial than if using innate sounds of the instrument.  And I get this exact same kind of hissing even if I use a USB stick to playback
          audio through a USB port on the GP400.  SO it appears to me to NOT be related to a "line-'in" or "audio cable" problem, because it occurs even if I use the
          piano's onboard record to USB function and then play back through the piano.  It does NOT occur if I use the pianos midi record function and play back
          through the piano.  I take that as an indication that something is screwy with the way the piano is processing any incoming sound, regardless of whether via
         digital signal or analog line in.  But I'm uncertain).

If there is buzzing audible, I'd suspect it's probably because the output from the laptop is a headphone output, not a line out, and isn't well matched to the line input on the Casio. This could likely by solved by using a USB sound module that does have an actual line output.

                         Where DOES The USB sound module ATTACH?  Confused about this.

If the sound using the audio connection alone is clean  (ME: IT ISN'T)   , and the buzzing only appears when the MIDI connection is installed, then that would confirm the cause as a ground loop (common earth path). The best solution for this is, as has been suggested, using a proper MIDI interface which has optical isolation, as per the MIDI spec. MIDI was designed to work using opto-isolators to avoid having problems with hum loops.   ODDLY, A HUM ELIMINATOR GETS RID OF THE HUM..... ALMOST ENTIRELY....

I get this effect myself at times in my music monitoring via my KRK powered monitors. It's a bit annoying that it's there, but as it is only the monitoring that has that effect at times, I haven't worried about going through, diagnosing and changing the existing layout to reduce or eliminate it.

levinite wrote:

Eli26 wrote:

I will try that when I get home.  I am wondering though if I explained incorrectly.  Moving the plugs has no impact on the sound.  I meant that if the wire is ONLY plugged into the line in jacks, and is not plugged in, then if I handle the plug end, it buzzes, and sometimes if it just lies there it buzzes.  Moving the cable around this way or that way can increase or decrease the buzzing.

I did misinterpret what you said. But it is still not clear what the situation is. Platypus gave a procedure to try to isolate the problem, but your answers are not clear at least to me.

First, disconnect the midi cable completely and connect only your Kindle (battery only), do you still get the hum? Does moving, jiggling or touching the cable make any difference? How loud is the hum in this case?

some more info: With MIDI not plugged in at all, and just the audio cable, there seems to be small amount of background hissing when computer audio is playing through the speakers.  It can be minimized by lowering the DP volume as I raise the computer volume to compensate for that.

When I then plug in USB cable to bring midi data to the laptop, at first I hear som ehigh pitched whiny noises and then steady buzz.  The buzz seems to be from 6-14 seconds at a time, with breaks of several seconds.  (This is largely eliminated when I use the mpow noise eliminator. )

Even with the noise eliminator to get rid of the buzzing, there is still a small amount of background hiss when audio is played and for several seconds later.

Some hiss from a computers headphone jack is not unexpected.
If you really want help you should follow the outlines given. It doesn't help to guess how you have everything set up.

Eli26 wrote:

levinite wrote:

"If I move it around a bit, there is little to no noise."
There it is.
When you move it you change the connection resistance or less likely the cable resistance. The connections do not have proper contacts. Try cleaning the connector ends with contact cleaner. Some of the inside connections may also be dirty. In general, try to connect everything to a common ground which should also help reduce noise. You want a low resistance shield but if the wire is too stiff it can make it harder for the contact to sit well in the receptacle which again can affect the contact resistance.

I will try that when I get home.  I am wondering though if I explained incorrectly.  Moving the plugs has no impact on the sound.  I meant that if the wire is ONLY plugged into the line in jacks, and is not plugged in, then if I handle the plug end, it buzzes, and sometimes if it just lies there it buzzes.  Moving the cable around this way or that way can increase or decrease the buzzing.

I did misinterpret what you said. But it is still not clear what the situation is. Platypus gave a procedure to try to isolate the problem, but your answers are not clear at least to me.

First, disconnect the midi cable completely and connect only your Kindle (battery only), do you still get the hum? Does moving, jiggling or touching the cable make any difference? How loud is the hum in this case?

some more info: With MIDI not plugged in at all, and just the audio cable, there seems to be small amount of background hissing when computer audio is playing through the speakers.  It can be minimized by lowering the DP volume as I raise the computer volume to compensate for that.

When I then plug in USB cable to bring midi data to the laptop, at first I hear som ehigh pitched whiny noises and then steady buzz.  The buzz seems to be from 6-14 seconds at a time, with breaks of several seconds.  (This is largely eliminated when I use the mpow noise eliminator. )

Even with the noise eliminator to get rid of the buzzing, there is still a small amount of background hiss when audio is played and for several seconds later.

Unfortunately I was never able to resolve my issues with noise until I connected a (cheap) USB audio interface to (ancient) external speakers. Eagerly awaiting an upgrade of this setup for Christmas!

What audio interface did you use? And if you are just using headphones, does the interface improve the sound vs direct from laptop to headphones?  Lastly, are you also a casio owner?

levinite wrote:

Eli26 wrote:

The cable quality MAY be part of it. If it's plugged into the casio unit and not plugged into anything else, there is often a loud buzzing.... depends on how I position the cable. If I move it around a bit, there is little to no noise.if I unplug it, thee is zero noise (so it's no inherent to the unit)If I handle the 3.5 mm plug of the cable, it's  a LOUD buzz. If I plug it into a laptop, a kindle, etc, the hum decreases, but is still there.   And if I use the mpow noise eliminator, it gets rid of most of it.  Based on thta, do you think it's the cable?  (But note that the cable which I use, linked below, gets really nice ratings and reviews mention that they must be well-shielded becuse they ELIMINATE buzzing).... 
https://www.amazon.com/gp/product/B00ZK...&psc=1

I will have to follow your protocol carefuly when I get home later, and will post.....

"If I move it around a bit, there is little to no noise."
There it is.
When you move it you change the connection resistance or less likely the cable resistance. The connections do not have proper contacts. Try cleaning the connector ends with contact cleaner. Some of the inside connections may also be dirty. In general, try to connect everything to a common ground which should also help reduce noise. You want a low resistance shield but if the wire is too stiff it can make it harder for the contact to sit well in the receptacle which again can affect the contact resistance.

I will try that when I get home.  I am wondering though if I explained incorrectly.  Moving the plugs has no impact on the sound.  I meant that if the wire is ONLY plugged into the line in jacks, and is not plugged in, then if I handle the plug end, it buzzes, and sometimes if it just lies there it buzzes.  Moving the cable around this way or that way can increase or decrease the buzzing.

I did misinterpret what you said. But it is still not clear what the situation is. Platypus gave a procedure to try to isolate the problem, but your answers are not clear at least to me.

First, disconnect the midi cable completely and connect only your Kindle (battery only), do you still get the hum? Does moving, jiggling or touching the cable make any difference? How loud is the hum in this case?

If moving the 1/4" plugs where they plug into the Casio doesn't make the buzzing come and go, that suggests there isn't a problem such as a cracked solder joint inside the Casio. If it is bending or applying tension to the flexible cable itself that provokes the buzzing to stop and start, that strongly indicates the shielding braid inside the cable has fractured and is only making intermittent contact.

Apart from being able to test it with a meter, the way to prove this would be to borrow another of that type of cable to try, and see if the buzzing stops.

Eli26 wrote:

Platypus wrote:

You do seem to have had a few problems with that Casio unit?

A process of elimination is usually needed to work out ground loop/hum problems. If I was trying to diagnose, I would first double check the audio cable itself is OK, simply plug the cable alone into the line inputs of the Casio. Because it's just an open cable, you could get a small amount of hum/noise, but if you hear as much hum with nothing connected as you get when it's connected, the cable itself may be the problem. If it's fairly quiet, move on.

Next determine whether the hum/buzz is present without the MIDI connection, i.e. just using the Casio as an amplifier for the laptop sound output. You can of course test by just having them connected together, with the laptop running on battery. There should be no significant sound evident, until the laptop plays a sound source, e.g. music track or Pianoteq triggered from the integral mouse keyboard.

If there is buzzing audible, I'd suspect it's probably because the output from the laptop is a headphone output, not a line out, and isn't well matched to the line input on the Casio. This could likely by solved by using a USB sound module that does have an actual line output.

If the sound using the audio connection alone is clean, and the buzzing only appears when the MIDI connection is installed, then that would confirm the cause as a ground loop (common earth path). The best solution for this is, as has been suggested, using a proper MIDI interface which has optical isolation, as per the MIDI spec. MIDI was designed to work using opto-isolators to avoid having problems with hum loops.

The cable quality MAY be part of it. If it's plugged into the casio unit and not plugged into anything else, there is often a loud buzzing.... depends on how I position the cable. If I move it around a bit, there is little to no noise.if I unplug it, thee is zero noise (so it's no inherent to the unit)If I handle the 3.5 mm plug of the cable, it's  a LOUD buzz. If I plug it into a laptop, a kindle, etc, the hum decreases, but is still there.   And if I use the mpow noise eliminator, it gets rid of most of it.  Based on thta, do you think it's the cable?  (But note that the cable which I use, linked below, gets really nice ratings and reviews mention that they must be well-shielded becuse they ELIMINATE buzzing).... 
https://www.amazon.com/gp/product/B00ZK...&psc=1

I will have to follow your protocol carefuly when I get home later, and will post.....

"If I move it around a bit, there is little to no noise."
There it is.
When you move it you change the connection resistance or less likely the cable resistance. The connections do not have proper contacts. Try cleaning the connector ends with contact cleaner. Some of the inside connections may also be dirty. In general, try to connect everything to a common ground which should also help reduce noise. You want a low resistance shield but if the wire is too stiff it can make it harder for the contact to sit well in the receptacle which again can affect the contact resistance.

I will try that when I get home.  I am wondering though if I explained incorrectly.  Moving the plugs has no impact on the sound.  I meant that if the wire is ONLY plugged into the line in jacks, and is not plugged in, then if I handle the plug end, it buzzes, and sometimes if it just lies there it buzzes.  Moving the cable around this way or that way can increase or decrease the buzzing.

Platypus wrote:

You do seem to have had a few problems with that Casio unit?

A process of elimination is usually needed to work out ground loop/hum problems. If I was trying to diagnose, I would first double check the audio cable itself is OK, simply plug the cable alone into the line inputs of the Casio. Because it's just an open cable, you could get a small amount of hum/noise, but if you hear as much hum with nothing connected as you get when it's connected, the cable itself may be the problem. If it's fairly quiet, move on.

Next determine whether the hum/buzz is present without the MIDI connection, i.e. just using the Casio as an amplifier for the laptop sound output. You can of course test by just having them connected together, with the laptop running on battery. There should be no significant sound evident, until the laptop plays a sound source, e.g. music track or Pianoteq triggered from the integral mouse keyboard.

If there is buzzing audible, I'd suspect it's probably because the output from the laptop is a headphone output, not a line out, and isn't well matched to the line input on the Casio. This could likely by solved by using a USB sound module that does have an actual line output.

If the sound using the audio connection alone is clean, and the buzzing only appears when the MIDI connection is installed, then that would confirm the cause as a ground loop (common earth path). The best solution for this is, as has been suggested, using a proper MIDI interface which has optical isolation, as per the MIDI spec. MIDI was designed to work using opto-isolators to avoid having problems with hum loops.

The cable quality MAY be part of it. If it's plugged into the casio unit and not plugged into anything else, there is often a loud buzzing.... depends on how I position the cable. If I move it around a bit, there is little to no noise.if I unplug it, thee is zero noise (so it's no inherent to the unit)If I handle the 3.5 mm plug of the cable, it's  a LOUD buzz. If I plug it into a laptop, a kindle, etc, the hum decreases, but is still there.   And if I use the mpow noise eliminator, it gets rid of most of it.  Based on thta, do you think it's the cable?  (But note that the cable which I use, linked below, gets really nice ratings and reviews mention that they must be well-shielded becuse they ELIMINATE buzzing).... 
https://www.amazon.com/gp/product/B00ZK...&psc=1

I will have to follow your protocol carefuly when I get home later, and will post.....

"If I move it around a bit, there is little to no noise."
There it is.
When you move it you change the connection resistance or less likely the cable resistance. The connections do not have proper contacts. Try cleaning the connector ends with contact cleaner. Some of the inside connections may also be dirty. In general, try to connect everything to a common ground which should also help reduce noise. You want a low resistance shield but if the wire is too stiff it can make it harder for the contact to sit well in the receptacle which again can affect the contact resistance.

I had the same problem with my GP-500 and ground buzzing.
I solved it with: https://shop.cesys.com/en/PC-technology...LATOR.html

-----------------------
Casio  USB-Midi  >>>>> CESYS Adapter >>>>>> PC
Casio  Line-IN     <<<<<<<<<<<<<<<<<<<<<<<<  PC HiRES Dac
----------------------

You do seem to have had a few problems with that Casio unit?

A process of elimination is usually needed to work out ground loop/hum problems. If I was trying to diagnose, I would first double check the audio cable itself is OK, simply plug the cable alone into the line inputs of the Casio. Because it's just an open cable, you could get a small amount of hum/noise, but if you hear as much hum with nothing connected as you get when it's connected, the cable itself may be the problem. If it's fairly quiet, move on.

Next determine whether the hum/buzz is present without the MIDI connection, i.e. just using the Casio as an amplifier for the laptop sound output. You can of course test by just having them connected together, with the laptop running on battery. There should be no significant sound evident, until the laptop plays a sound source, e.g. music track or Pianoteq triggered from the integral mouse keyboard.

If there is buzzing audible, I'd suspect it's probably because the output from the laptop is a headphone output, not a line out, and isn't well matched to the line input on the Casio. This could likely by solved by using a USB sound module that does have an actual line output.

If the sound using the audio connection alone is clean, and the buzzing only appears when the MIDI connection is installed, then that would confirm the cause as a ground loop (common earth path). The best solution for this is, as has been suggested, using a proper MIDI interface which has optical isolation, as per the MIDI spec. MIDI was designed to work using opto-isolators to avoid having problems with hum loops.

The cable quality MAY be part of it. If it's plugged into the casio unit and not plugged into anything else, there is often a loud buzzing.... depends on how I position the cable. If I move it around a bit, there is little to no noise.if I unplug it, thee is zero noise (so it's no inherent to the unit)If I handle the 3.5 mm plug of the cable, it's  a LOUD buzz. If I plug it into a laptop, a kindle, etc, the hum decreases, but is still there.   And if I use the mpow noise eliminator, it gets rid of most of it.  Based on thta, do you think it's the cable?  (But note that the cable which I use, linked below, gets really nice ratings and reviews mention that they must be well-shielded becuse they ELIMINATE buzzing).... 
https://www.amazon.com/gp/product/B00ZK...&psc=1

I will have to follow your protocol carefuly when I get home later, and will post.....