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Patchbay noise?

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Patchbay noise?

Postby vetsdiggy » Thu Jan 10, 2013 6:43 pm

Hey folks
I'm in the process of rewiring my studio, as I got some new converters and desk, so took the opp to have a new year fresh start, pull it all out and go from scratch.

I've always used patch bays (only ever had beringer ones) and never had any problems with them, but now this.....

I now have apogee rosetta 800 and a small Trident 8t 8, which is a reduction in chennels for me (Ihad 24 before). I use synths and drum machines so as many chans I can use while tracking is important, so diddn't want to hard wire the apogee outs to the lines, or tape returns on the desk.

I therefore decided to have the apogee outs going to a PB, normald to the line ins on the desk, so I can break the path with any synths ect I wish, but still have a short signal path back to the desk from the DAW for summing when required....

Straight forward enough, but now I'm getting a hiss, which I'm sure shouldn't be present.
Its quite noticable, and at first supected it was the apogee, as that seemed to be where it was coming from.
I then tried all sorts of different combinations to try and find the source of the hiss, and all roads lead to the patch bay.....? If I take it out the chain, the hiss is gone.....

I've never had this level of noise from the bays before, why would it be doing this. Could they be picking up the noise from else where and conducting it?

I'm stumped.

I can go into more detail if you need it, I know these things are complicated, and loads of factors could be involved.

Any help would be great.
I just want to get back to making music, and stop seeing cables every time I close my eyes!!!!!!

Cheers
Steve
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Re: Patchbay noise?

Postby Hugh Robjohns » Thu Jan 10, 2013 10:54 pm

Could well be a ground loop issue through the patch bay. A lot of converters generate quite a bit of ultrasonic noise energy which could be finding its way into other equipment via the patch bay.

Hugh
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Re: Patchbay noise?

Postby vetsdiggy » Thu Jan 10, 2013 11:45 pm

Thanks Hugh..
It doesn't sound like a ground, more just hiss, or could that still be the case?
It actually sounds as though (I know this shouldn't be possible) the patch bay is amplifying the noise floor...?
If I connect the outs from the 800 directly to the desk line ins.... no hiss (or at least no more than you'd expect), but as soon as I put the PB in the chain, I have the hiss?
I tried another patch bay and was the same. even tried a patch bay with nothing else connected and not even in the rack with any of my other kit... same storey.

This is killing me.

Its my birthday in an hour too.
Bugger.

Thanks again for any suggestions.
Steve.
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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 12:52 am

Ground loops don't always produce hums. Ground loops basically allow any signals flowing around the ground circuitry to find its way into the equipment's audio circuitry, and those ground signals can actually e all manner of hums, hisses, buzzes, whines, and other noises generated by the connected equipment.

As I said previously, I'd be suspecting ultrasonic noise from the Apogee.

If there is no hiss with direct patching the. The most likely cause is the common grounding within the patch bay. Some patch bays allow you to isolate the grounds from each circuit, but I don't think that's an option in your case (worth checking, though). You might find that bonding the patch bay ground directly to the console ground or the mains safety ground helps. Or you might have to modify the cables between the converters and patch bay (and/or the patch bay and console) to break their screen connections at the destination ends.

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Re: Patchbay noise?

Postby vetsdiggy » Fri Jan 11, 2013 10:05 am

Ahh, that is starting to make sense then.
I'll look into that.What would be the best way to bond the `PB ground to the desk?
I hope that works, it should be less time consuming than doing all the cables!

Thanks again Hugh!
Steve
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Re: Patchbay noise?

Postby James Perrett » Fri Jan 11, 2013 11:27 am

Is everything balanced? I've had a similar issue when I tried to feed a balanced output to a balanced input with the wrong sort of unbalanced cable. The right sort of unbalanced cable or a fully balanced cable would work fine.

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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 12:08 pm

It depends on the mechanical design of both, but essentially it would involve running a modeartely chunky earth wire from the metalwork of the patchbay to that of the mixer, using appropriate eye-tags or similar and ensuring very good contact at both ends.

However, resolving ground loop problems can be hugely confusing, frustrating, apparently illogical, and time consuming... and you have to work through the system very carefully to arrive at the optimum solution.

I assume the Apoggee hardware is mounted in the same rack as the patch bay. It might be worthwhile removing other equipment from the rack and retesting to find out if the ground loop is via the connecting cables or via chassis coupling through the rack metalwork. If the latter, plastic 'humfrees' isolating the mounting bolts might be a better solution.

If you've not already done so, it would also be worth connecting the desk to the patch bay on its own to make sure that the common grounding at the patch bay isn't upsetting the desk in some way on its own -- it wouldn't be the first time!

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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 12:28 pm

James Perrett wrote:Is everything balanced? I've had a similar issue when I tried to feed a balanced output to a balanced input with the wrong sort of unbalanced cable.

Good point James -- I had assumed he was using balanced cables throughout, but seeing as he's talking about inherently unbalanced synths and things it could well be a problem with unbalanced connections.

Good thinking that man! ;)

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Re: Patchbay noise?

Postby vetsdiggy » Fri Jan 11, 2013 12:54 pm

Hey and thanks again both!
All the connections are ballanced, except for those from the synths
Which are on a different bay...
The frame holding all the gear is wooden (home made) and screws straight in so
no probs there.
It's worth saying that the noise goes away if I patch in something else
on the front of the bay to the desk, breaking the chain from the apogee
so it's only present when the apogee is in the path.... I.e. it's not just present on the whole bay regardles!


Thanks for your help!
Steve!
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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 1:07 pm

vetsdiggy wrote:It's worth saying that the noise goes away if I patch in something else
on the front of the bay to the desk, breaking the chain from the apogee
so it's only present when the apogee is in the path....

Okay, so it doesn't happen when you plug the apogee direct to the desk, and it doesn't happen with other sources connected to the desk via the patch bay... but it is a problem when connecting the apogee to the desk via the patch bay.

So it looks like a grounding issue with the apogee via the patch bay.

Can I ask you to see what happens with a simple experiment, please?

Connect the patch bay to the desk in the normal way. I presume that will be quiet and acceptable.

What then happens if you only connect one apogee output up to the patch bay and on to the desk? Do you still get the noise (I'm expecting not...)

And secondly, how does the noise change as you plug other apogee channels into the patch bay and through to the desk?

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Re: Patchbay noise?

Postby vetsdiggy » Fri Jan 11, 2013 3:24 pm

hey Hugh, just done this test and its no different?
I still have the noise?

I'm assuming I did it right...?
I unplugged all connections from apogee to PB (all ins and outs) but left all desk line ins running from the PB, then connected one out from the apogee to the PB as to come down line in one on the desk, then replace line in two on the desk with a line direct from the apogee....?

Cheers
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Re: Patchbay noise?

Postby vetsdiggy » Fri Jan 11, 2013 4:06 pm

Also here is an interesting development.....

I inserted a DI box in the chain between the apogee and the PB (keeping the rest identical) so I could see what might happen if if I lifted the ground on the DI. No noise.... But no noise regardless of the ground on the DI box being lifted or not.
It seems that the DI box being in the chain before the apogee hits the PB removes the noise , with or with out the lift?

Plus I just tried it between the PB and the desk aswell and its the same storey...?

Help!
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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 4:31 pm

vetsdiggy wrote:I unplugged all connections from apogee to PB (all ins and outs) but left all desk line ins running from the PB...

And that was quiet, yes? No hiss?

...then connected one out from the apogee to the PB as to come down line in one on the desk

And did the noise come back at that point, with just the one output from the Apogee connected?

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Re: Patchbay noise?

Postby Hugh Robjohns » Fri Jan 11, 2013 4:37 pm

vetsdiggy wrote:I inserted a DI box in the chain between the apogee and the PB



Presumably this DI box is a normal unbalanced input version? If so it's muddying the waters unhelpfully... But it is also possible that it has a curtailed HF response and is preventing some ultrasonic energy getting into the system.

As I said earlier... these kinds of problems can be proper devils to resolve!

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Re: Patchbay noise?

Postby vetsdiggy » Fri Jan 11, 2013 4:51 pm

Yes the niose came as soon as I put just one output to the desk via the PB..

Also yes the DI was unbal input.

However this did lead me to think it could be a ballance issue?

This is reinforced by the fact that now when I try a mono signal sent unpanned out from Logic down a stereo output (so equal signal each chan), but run one direct to the desk and one through the PB (no DI in any chain), I notice that not only do I have hiss on just the chan run via the OB, but I also have a significant drop in signal level?

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