PlanetZ forums - scopeusers.com

Finally after fixing my freezing probs i have another sort of annoyance:

upon loading the default scope project, when i look in the mixer, the channel connected to luna analog in shows as if a signal is passing through it (although nothing is connected to the analog ins at this stage)
is this normal behaviour?

when i do connect my sampler to analog in, the vu meter rises and stabilizes on something like -43db... also a pretty loud sound which resembles something like a sawwave can be heard when i turn my speakers at a high level....

could this be the result of a bad audio cable?

Can be cabels but also all components in your computer generates high frequence noise.
But -43db seems a bit too much for me, here I have a noise level around -60db.

For example when I move the stm mixer with my mouse around the noise level rises.

Maybe some better cables and/or isolating somehow the SFP cards can help here but I am not a hardware guru.
I just disconnect the Analog Source when I don´t need it, that reduces the noise a bit.

I am sure other will join in here and can go more into the details.


_________________
Music starts where any language ends

<font size=-1>[ This Message was edited by: ChrisWerner on 2004-09-13 07:02 ]</font>

could it be that your computer is somehow alongside your monitor?

No, my computer is sitting low almost on the floor while the monitor is sitting on the table.

one thing i've tried (actually by accident) is i connected what supposed to be connected to the analog out (output to speakers) into the analog in. this didn't produce the same effect as before, but showed the normal -85db ... could be that my sampler connected at the end of the audio cable is producing some sort of noise that causes this VU meter rise...?

it could be the cable, but it could also be a ground loop between your computer and sampler. are they plugged into different outlets? it could alos be a bad jack(open ground) on the sampler. i'm assuming that the noise is in the 60hz range....

so what is then your suggestion ?

try to change cables first?

how do i handle all those "ground loops" and such?

there is a thread about this very subject, every possible reason is discussed including the position of the stars.
do a search

A good ref for ground problems:-

http://www.rane.com/note110.html

Is the noise there always even if the sampler is off?

bassdude - the noise remains no matter if sampler is on/off. as long as the cable is connected to analog in, it shows noise coming in....

i will do a search to find the thread as mentioned here.

thanks.

Ok, you have ground problems then. Is the noise a hum (50/60Hz) or is it like interference (RF)?
If it's a hum, then you have a ground loop. This is easy fixed.
If it's RF then your sampler is acting as an antenna picking up all sorts of stuff. This is a bit harder to fix and, assuming the interconnect cable is ok, typically indicates a bad earth connection somewhere in the unit itself, in the power cable or house wiring (assuming no plug-pack style power supply).

For a ground loop, try disconnecting the shield (ground) connection on the interconnecting cable as described in the Rane Note 110 (Don't disconnect ground on power cables). If the noise disappears, then that's your answer. Modify a cable so at one end there is no ground connection and use that for the interconnect.

For RF I would grab a spare cable and touch one end to a known good earth and the other end to an exposed metal part of the sampler's chassis to see if the RF disappears. If it does then you know you have a bad earth connection so I would try replacing the power cable or plug into a known good wall socket. If this is no good or the sampler uses a plug-pack style powersupply, then it might be time to either take it to a qualified service person to get it looked at or grab a soldering iron, pop the lid off and start hunting for dry joints etc etc.

<font size=-1>[ This Message was edited by: bassdude on 2004-09-14 19:55 ]</font>

Just to clarify: with the sampler off, the noise is still there? But when you remove the cables completely it's down to -85 db readings in the mixer?

I find it hard to believe that a sampler that is off, with whatever cabling configuration, would cause a ground loop.

As well, without a signal present, any interference (RFI or EMI) would presumably have the same effect on hot + cold + shield channels, effectively cancelling out.

Lysergide can you verify that:

1) the noise is -85 db below clip when there is no cable connected to the computer

2) the noise is -43 db below clip when the sampler is on

3) the noise is -43 db below clip when the sampler is off

Cheers,

Johann

....
I find it hard to believe that a sampler that is off, with whatever cabling configuration, would cause a ground loop.

You don't need power to be applied to have a ground loop. The loop is formed by the pyhsical connections via the shield of the signal cable, the chassis of the sampler, the earth of the power cord, the earth of the house wiring etc etc.

As well, without a signal present, any interference (RFI or EMI) would presumably have the same effect on hot + cold + shield channels, effectively cancelling out.

That only works if the RF is induced from outside a balanced path eg balanced cable. If the noise is induced within the equipment, it becomes part of the audio signal itself, and travels down the cable as if it is part of the normal audio signal. If that equipment has a metal chassis that isn't earthed correctly or the internal circuit's lose ground thru bad earth connection, dry joints etc, then the equipment itself becomes susceptible to RF interference. Kind of like walking up to fluorescant lights with an electric guitar.

On 2004-09-14 23:01, bassdude wrote:

....
I find it hard to believe that a sampler that is off, with whatever cabling configuration, would cause a ground loop.

You don't need power to be applied to have a ground loop. The loop is formed by the pyhsical connections via the shield of the signal cable, the chassis of the sampler, the earth of the power cord, the earth of the house wiring etc etc.

You remove one path (earth) when the circuit is broken / power is turned off. It is still possible to have a ground loop, but in this small scenario it seems unlikely to me. I'm no expert, though, so it's certainly worth trying all possibilities.

As well, without a signal present, any interference (RFI or EMI) would presumably have the same effect on hot + cold + shield channels, effectively cancelling out.

If the noise is induced within the equipment, it becomes part of the audio signal itself, and travels down the cable as if it is part of the normal audio signal.

But the equipment is OFF! That was my whole point.

the ground can still be connected(to the case) with the power off.

On 2004-09-15 14:46, blazesboylan wrote:
You remove one path (earth) when the circuit is broken / power is turned off. ...

The only way the earth is broken is when you remove the power cable. When you switch power off you are usually only breaking the active, not the neutral or earth.
Actually that would be a good test. Leave the sampler turned off and pull out its *power* cable. If the noise disappears then it is a ground loop. If the noise is still there then its a ground/shielding problem.

But the equipment is OFF! That was my whole point.

It becomes passive now. If the metal case of the sampler is not grounded correctly, the internal connectors, wires, components, PCB tracks become exposed. Think of it like a passive electric guitar. Plug a guitar into an amp and walk up to a fluro and it makes a hell of a noise. Put the guitar into a earthed metal case and you don't get the noise.

Fair enough. This is good stuff to think about. It's not sufficient to turn off equipment when searching for noise sources. One really has to completely disconnect it! I had never really given that much thought before.

Cheers,

Johann

Tracking noise gets tricky sometimes.
But for ground loops, turning off is not enough. Physical disconnection is key.

Cheers.

<font size=-1>[ This Message was edited by: bassdude on 2004-09-17 10:01 ]</font>