Frustrating Grounding Problem (HISS/BUZZ/NOISE)

I recently purchased my first pair of studio reference monitors (Behringer TRUTH B2031A Active Monitors).  Previously, I used computer speakers for my monitoring needs. However, I’ve come across a few issues and problems with the studio monitors.

HISS/BUZZ/NOISE

I hooked up my monitors to my laptop.  They are making a terrible sound.  The problem is likely due to a grounding issue. The reason I think it’s a grounding problem is due to the fact that when I allow my laptop to operate on batteries (i.e. unplug the laptop power) the noise ceases.

My question now is how to fix this problem. One solution is to use a ground isolator. However, the problem with that is that cheap isolators color the sound, thereby defeating the purpose of having a flat-response reference monitor. I might as well use my computer speakers. The coloring problem can be solved by purchasing a high quality isolator. However, that will cost at least $200 and I just cannot afford that right now. I spent 500 on the monitors, im not gonna go spend 200 on an isolator. So, how else can I fix this problem?

Have you had a look at the ART DTI? They are pretty good value for money. Worth trying at low cost.

http://www.artproaudio.com/products.asp?type=90&cat=13&id=106

I'm sorry to have to tell you, but this effect is extremely common with laptops, and yes it all relates to the way the power supplies work. Somewhere, either here on on the Adobe forum, we had quite an extensive debate about this effect, and what to do about it - isolators don't always fix this completely either; it rather depends on the particular installation you've got.

The problem is that basically, the power supplies used with laptops are switch-mode devices, and they are completely isolated from ground as far as the safety earth is concerned. But as far as high frequency coupling, which is where all the noise comes from, the switcher is rather well coupled (capacitively) into one side of the output - which is connected to your audio device, and thence to your monitors. The monitors, I presume, have a safety earth connection. What happens is that all of the noise introduced capacitively into what is effectively the ground of the audio appears as an extra signal in series with the feeds to the monitors - whose input sockets are grounded.

The solution really is to make sure somehow that the extra power supply noise isn't coupled into the audio device outputs in the first place, and it's not unknown that the application of a separate ground connection specifically to the computer audio device can reduce the problem considerably - simply because all of the noise is then coupled back to ground before being fed to the monitors. The problem with some isolators is that they are fine as what's known as galvanic devices - they isolate the direct connection completely up to mains frequencies, but then start to fail, because the higher frequencies get coupled through them anyway to an extent. The only hope at that stage is that they get coupled as what is known as a 'common-mode' signal - which means that if your monitors accept a properly balanced input, the noise will then cancel out.

To give you an idea of what can happen, and why the isolators don't always work, I'll tell you what happens here if I don't do anything about it. The capacitive coupling effect of the laptop's power supply is so bad that without the computer or sound device even turned on, or even connected, the noise generated between neutral and ground is fed back down the mains cable, and interposes itself between the monitor preamp and power amp grounds quite audibly - and no addition of any isolating devices makes a scrap of difference to this. The only way to reduce the effect is to take account of the grounding conditions, and arrange them so that this induced signal doesn't get into the soundcard/monitor ground at all. And I have to say that it took quite a while, and a lot of experiments, before I could reduce the effect to a reasonable level.

All of the good solutions look for all the world like using a sledgehammer to crack a nut - but in reality, that nut is pretty hard to crack. I'm not saying that you shouldn't try isolation transformers - you may be one of the lucky ones for whom they provide a workable fix. But I wouldn't go as far as to call this a solution - one of those would involve eliminating the source of the problem, not isolating it. That's possible, but also not that cheap. You either use a linear power supply (which will have to be quite a chunky thing to run your laptop), or use one of the more bizarre solutions, like running your laptop from 3 x 6v car batteries, recharged from a floating power supply when the laptop's switched off.

Believe me, if there was a universal fix for this, I would tell you - but so far, all attempts to find one have failed, even though we know what causes it.

I should also add that it isn't just laptop power supplies that cause this effect - the small switch-mode supply for the MOTU traveller causes it too.

I'm sorry to have to tell you, but this effect is extremely common with laptops, and yes it all relates to the way the power supplies work.

This implies that I can solve my problem by using a desktop computer. Am I correct in Assuming this?

Have you had a look at the ART DTI? They are pretty good value for money. Worth trying at low cost.

http://www.artproaudio.com/products.asp?type=90&cat=13&id=106

A long time ago someone gave me one of these. I didn't know what it was. I stashed it away somewhere...now I just have to find it and try it.

I use the Rapco LI-100 for connecting laptops to my PA or recording rig. It works very well and has all of the features I need.

http://www.rapco.com/Catalog2/deviceBoxes.aspx#

This implies that I can solve my problem by using a desktop computer. Am I correct in Assuming this?

Pretty much, yes. Desktops don't have anything like the problems, because there's a low impedance common ground bond for everything. Also, the power supplies (still switch-mode) generally have better filtering, so there's far less interference coupled into the ground connection anyway. No computer system is perfect from this POV - and the moment you connect anything ground-referenced to your system, you have to be more careful to avoid strange noises anyway. This is almost certainly why your previous monitors didn't give you a problem - the inputs on most computer monitors are effectively isolated from everything to do with supply ground.

In theory, a good isolated-ground transformer system that's run in truly balanced mode should be able to isolate this problem completely, by eliminating the common mode noise signals. But the chances of the Behringer inputs being this well balanced aren't good, so I wouldn't hold out for a total solution by that means. And anyway, it can get in via other means, as it does here if I'm not careful.

The solution really is to make sure somehow that the extra power supply noise isn't coupled into the audio device outputs in the first place...

The above indicates that theoratically another possible solution might be to power my soundcard through some other means...perhaps by using an external USB powered soundcard. However, the following negates this idea:

The capacitive coupling effect of the laptop's power supply is so bad that without the computer or sound device even turned on, or even connected, the noise generated between neutral and ground is fed back down the mains cable, and interposes itself between the monitor preamp and power amp grounds quite audibly - and no addition of any isolating devices makes a scrap of difference to this. The only way to reduce the effect is to take account of the grounding conditions, and arrange them so that this induced signal doesn't get into the soundcard/monitor ground at all. And I have to say that it took quite a while, and a lot of experiments, before I could reduce the effect to a reasonable level.

So will the USB cable simply continue transferring the high frequency signal, thereby failing to solve the problem?


I am beginning to question my decision to purchase studio monitors. They don't even sound that flat too me (too much bass), but I probably shouldn't pass judgment on them yet. I should wait a few weeks/months and mix a few songs first. Another issue I'm having with the monitors is that the only way to adjust the volume is either through the back or by adjusting my soundcard settings in windows. Also, there's no phone jack so I can't easily plug in my headphones for monitoring purposes during recording (I have to go through the same laptop jack that I use for the monitors). This is merely an inconvenience, but it exasperates my frustration with these monitors. An external soundcard with a an external volume switch may assist me in resolving some of the minor issues. Or is there some other solution (e.g. using an amp, though the Truths are already amplified)?

The capacitive coupling effect of the laptop's power supply is so bad that without the computer or sound device even turned on, or even connected, the noise generated between neutral and ground is fed back down the mains cable, and interposes itself between the monitor preamp and power amp grounds quite audibly - and no addition of any isolating devices makes a scrap of difference to this. The only way to reduce the effect is to take account of the grounding conditions, and arrange them so that this induced signal doesn't get into the soundcard/monitor ground at all. And I have to say that it took quite a while, and a lot of experiments, before I could reduce the effect to a reasonable level.

So will the USB cable simply continue transferring the high frequency signal, thereby failing to solve the problem?

It doesn't negate the idea - it's just not a simple situation. You have to bear in mind that the interference isn't transmitted as a 'wanted signal' as such, but as a noise in the ground connection that can, under some circumstances, be cumulative. If you start by supplying your external card via a USB/Firewire power supply that's correctly (ie solidly) grounded in the first place, then by and large you don't get problems - or if you do, you can solve them with an isolating transformer. Because of the possibly cumulative nature though, the more power supplies you add to what was an unsuppressed problem in the first case, the worse it gets. But if your interconnect has its braid firmly grounded, and the noise signal hasn't interposed itself onto the digital lines as well, then you don't get the problem - or at least, it's very much reduced.

But there's the rub - it's that 'interposed' thing. Because, the problem can be exacerbated by all sorts of other internal issues to do with ground separation within the laptop as well, and this can make what's already quite a complicated situation even worse. That's why all that any of us could do is to outline what the problem is, but not solve it necessarily - all installations are different. It does generally help though if all mains connections for everything are supplied from the same source, and joined together pretty closely. Quite often, just rearranging the power connectors can make a difference - it's that tricky.

I am beginning to question my decision to purchase studio monitors. They don't even sound that flat too me (too much bass), but I probably shouldn't pass judgment on them yet. I should wait a few weeks/months and mix a few songs first. Another issue I'm having with the monitors is that the only way to adjust the volume is either through the back or by adjusting my soundcard settings in windows. Also, there's no phone jack so I can't easily plug in my headphones for monitoring purposes during recording (I have to go through the same laptop jack that I use for the monitors). This is merely an inconvenience, but it exasperates my frustration with these monitors. An external soundcard with a an external volume switch may assist me in resolving some of the minor issues. Or is there some other solution (e.g. using an amp, though the Truths are already amplified)?

There are several things to say about this. The first is that the amount of bass you get from monitors in most small rooms is extremely dependent on how closely you position them to the corners of the room - all you are experiencing is the reaction of the room to monitors that are exciting more of its acoustic properties. So, if you stick monitors designed to run in more or less a free field in the corners then yes, they appear to be bass-heavy. So, you follow the recommendations on page 7 of the manual, and use the room compensation switch appropriately. Chances are that your room will need bass-trapping as well - this is the other common cause of people thinking that there's too much bass, and this also means that the sweet spot (where everything actually sounds correct) is rather smaller than it should be, because any standing waves will be rather more pronounced. (I could tell you a recent, slightly embarrassing for the people concerned, tale here, but it would look like name-dropping and I tend not to do that...)

Controlling the levels is a pain if you are connecting any active monitors directly to a soundcard. The normal solution is to use a passive volume control, or better still, something like a Mackie Big Knob. This will let you control the monitor level and give you a separate headphone amp as well - it's designed to get over precisely the problems you are having.

There are several things to say about this. The first is that the amount of bass you get from monitors in most small rooms is extremely dependent on how closely you position them to the corners of the room - all you are experiencing is the reaction of the room to monitors that are exciting more of its acoustic properties. So, if you stick monitors designed to run in more or less a free field in the corners then yes, they appear to be bass-heavy. So, you follow the recommendations on page 7 of the manual, and use the room compensation switch appropriately. Chances are that your room will need bass-trapping as well - this is the other common cause of people thinking that there's too much bass, and this also means that the sweet spot (where everything actually sounds correct) is rather smaller than it should be, because any standing waves will be rather more pronounced. (I could tell you a recent, slightly embarrassing for the people concerned, tale here, but it would look like name-dropping and I tend not to do that...)

I tried playing around with the setting on the back of the monitors (room compensation switches). It didn't suffice. However, as you mentioned, there are other factors to consider:

1) Placement - There is not much I can do about that. I'm working in a small room and there's very little maneuvering space.

2) Bass Traps - I dampened my room in various ways. However, I have not installed any bass traps yet. This is something I have to do and it may very well solve part of my problem.

Controlling the levels is a pain if you are connecting any active monitors directly to a soundcard. The normal solution is to use a passive volume control, or better still, something like a Mackie Big Knob. This will let you control the monitor level and give you a separate headphone amp as well - it's designed to get over precisely the problems you are having.

I looked into the Mackie Big Knob. It looks great! But I can't afford it (approximately $300).


Are there any other "passive volume controls" out there that are significantly cheaper?

The cheapest ones are the ones you build yourself.  Just a 10K stereo pot in a box with suitable connectors. However the stereo tracking may not be as good as an expensive properly designed one.

There are a couple of pot-only solutions, but if you are prepared to do a simple bit of wiring, then putting an Alps Blue Velvet pot (which will track very well) into a small box with 4 connectors ( 2 in, 2 out) is still cheaper, as ryclark suggests. I can provide details if necessary...

Alternatively, the cheapest solution including headphone monitoring I can find easily is the new M-Patch, which looks like quite a good deal, all things considered. Not that much more expensive than building something suitable in fact, by the time you've got all the hardware together. Half the price of a Big Knob...

Just to back up what Steve has said, I've always had success with home-built audio transformers in a die cast box for isolation and also never had problems with external USB or firewire units. But, I do know of people who have continued to have trouble no matter what they did, both with USB things and when using transformer isolators. There always has to be a bit of "suck it and see", I'm afraid.

In the only case where we succeeded against all the odds, the other person involved ended up getting hold of a linear power supply and having to use that.

WRT the other question, I've always suggested a small mixer where people have needed more control of levels. It always comes in handy in the long run, and anything from a decent manufacturer - eg Soundcraft - would be ideal. One of mine, the Spirit M4, came from Fleabay and it has been and still is marvellous. The older, smaller one I bought new in the days when I had a bit of cash to spend.   

Do your monitors have balanced inputs? If so then you can probably get rid of the noise by simply changing your cable wiring rather than by adding any more gizmos. Wire the signal to pin 2 or the tip of the balanced input and connect the screen to pin 3 or the ring of the balanced input while leaving pin 1 or sleeve of the balanced input disconnected. This wiriing configuration will break the ground loop and works well with my Acer laptop.

Cheers

James.