Topic: Noisefloor on the Display Meter

I just got a beautiful ADI-2 PRO FS, but I'm wondering about something.

The DB Meter on the Display always shows -72db of floor noise, even if all my equipment is turned off and only the ADI-2 Pro is switched on, how is this possible? Shouldn't the Noise Floor be around -119db (ADI-2 PRO FS specs)?


Thank you!

2

Re: Noisefloor on the Display Meter

It is. You either have something plugged in, or sample rates set to 192 kHz or higher.

Regards
Matthias Carstens
RME

3 (edited by KaiS 2020-05-07 12:08:15)

Re: Noisefloor on the Display Meter

Which input is selected - analog?
Anything connected there?


The meter does show the the real level, the following options are available:
• Post-FX: the DAC's output signal, including Vol., EQ and other DSP settings.
• Pre-FX: the selected input signal
• Dual: Both, finer outside lines Pre-, inner thick bars and numbers: Post

If you see -72dB this signal is feed into ADI-2 Pro from somewhere.
Disconnect the cables one by one to find it.



Here, on my ADI-2 Pro, Analog input, Meters Pre, show:
(All at Sample Rate 44.1 kHz)

Reference Level +4 dB
open (no cable connected): -97dB
Input pins 2/3 100Ω to GND pin 1 (Like ADI-2 output): -109dB

Reference Level +24 dB
open (no cable connected): -111dB
Input pins 2/3 100Ω to GND pin 1 (Like ADI-2 output): -111dB


Externally measured from ADI-2 Pro USB out:

Reference Level +4 dB
Input pins 2/3 100Ω to GND pin 1 (Like ADI-2 output).
-122,5 dBA RMS A-weighted
-118.5 dB RMS unweighted
-107 dB Peak unweighted

Reference Level +24 dB
Input pins 2/3 100Ω to GND pin 1 (Like ADI-2 output).
-124.7dBA RMS A-weighted
-120.4 dB RMS unweighted
-108 dB Peak unweighted


As you can see, the figures widely depend on the way a meter is working and calibrated.
For HiFi equipment usually the best possible figures are used: dBA RMS A-weighted.

4 (edited by dbot 2020-05-07 14:13:08)

Re: Noisefloor on the Display Meter

Hm, another thing that is rather suspicous sad
As soon as I unplug the cables from the Analog Input, there is a loud "brummen"/rumbling in my speakers, which goes away as soon as I replug the xlr cables into the Analog Inputs of the ADI-2

If I go to the EQ Screen, the Meter shows -110 on the Analog In, but as soon as I go to the Main Out Screen it shows -66.

Even Stranger: The ADE-2 is plugged into a Mackie Big Knob Passive Controller and if I have the Volume Knob at 12 o clock, the rumbling is the loudest, if I push it all the way to "Max", the rumbling becomes quieter and the floor noise louder.

This seems rather wierd, help

Re: Noisefloor on the Display Meter

the rumbling/brummen seems to be coming from the ADE-2, because when I unplug the speaker cables and hold them in the right hand and then just touch the cassis of th ADE-2 PRO fs, the rumbling appears again being transmitted by me. this doesn't happen if I touch any of my other gear. I also tried plugging the powersupply into another plug, but that didn't make any difference.

Re: Noisefloor on the Display Meter

The culprit seemed to be my passiv Big Knob controller, strange though, don't have this Problem with any other Input Source.
I'll do more tests tomorrow.

7 (edited by KaiS 2020-05-08 16:24:36)

Re: Noisefloor on the Display Meter

To sort this out I need to know all the details, what is plugged to each of ADI-2 Pro's in's and out's when in normal use?



Meanwhile I can explain why you hear hum ("Brummen") when you unplug the speaker cables and touch ADI-2 Pro:

ADI-2 Pro's PSU, by design, is not connected to ground.
This avoids hum from from ground loops when plugged to equipment that is grounded, like most power amps and powered speakers.

Usually the metal housing of XLR plugs is not connected to screen.
When you touch the unplugged XLR housing and ADI-2 Pro, a very tiny, non dangerous amount of power line stray current makes it's way from ADI-2's PSU's to the unscreened XLR housing and creeps into the signal line.

Once plugged in, the XLR housing is grounded and this effect goes away completely.



Except -  and now we come back to your original problem - if none of your devices is connected to ground.
Then your whole system lives on a floating voltage potential somewhere between ground and 230V / 50Hz hum.
For the Mackie Big Knob e.g. this could present a problem.

You can easily test it:
Lightly sweep above a metal surface of any of the involved devices, you feel a jittery sensation in your finger if this voltage is present.

If you have a voltmeter you can even measure the voltage against ground.



Other possibility:
You have to many ground connections and suffer from a ground loop.


REMARK:
For simplification I do use the term "ground" here throughout, even if technically it's partly "earth".

8 (edited by dbot 2020-05-11 19:49:03)

Re: Noisefloor on the Display Meter

KaiS wrote:

To sort this out I need to know all the details, what is plugged to each of ADI-2 Pro's in's and out's when in normal use?



Meanwhile I can explain why you hear hum ("Brummen") when you unplug the speaker cables and touch ADI-2 Pro:

ADI-2 Pro's PSU, by design, is not connected to ground.
This avoids hum from from ground loops when plugged to equipment that is grounded, like most power amps and powered speakers.

Usually the metal housing of XLR plugs is not connected to screen.
When you touch the unplugged XLR housing and ADI-2 Pro, a very tiny, non dangerous amount of power line stray current makes it's way from ADI-2's PSU's to the unscreened XLR housing and creeps into the signal line.
Once plugged in, the XLR housing is grounded and this effect goes away completely.



Except -  and now we come back to your original problem - if none of your devices is connected to ground.
Then your whole system lives on a floating voltage potential somewhere between ground and 230V / 50Hz hum.
For the Mackie Big Knob e.g. this could present a problem.

You can easily test it:
Lightly sweep above a metal surface of any of the involved devices, you feel a jittery sensation in your finger if this voltage is present.

If you have a voltmeter you can even measure the voltage against ground.



Other possibility:
You have to many ground connections and suffer from a ground loop.


REMARK:
For simplification I do use the term "ground" here throughout, even if technically it's partly "earth".

Thanks KaiS,

I've been sick so only now able to take some measurments.

My Setup up is as follows: I have a Motu 16A Interface, who's 16 outputs get summed in a Dangerous 2-Bus that's connected to the RME ADI-2 PRO FS at the moment (Ideally my SPL Kultube and Vitalizer would go inbetween in the future, but have been left out for testing).


If I have the RME connected via USB an the Outputs go to my Amp/Speakers I get the following readings (the values are always jumping around a bit and never stay still btw):

No Analog Inputs connected to the RME => -100 / -99 @ +4dBU REF — -111 / -112 @ +24dbU REF
Motu 16A (powered on) going into Dangerous 2-BUS going into RME  =>  -77DB / -77DB @ +4dbU —  -97 / - 97 @ +24dBU REF
Motu 16A (switched off) going into Dangerous 2-BUS going into RME => -57 / -66 @ +4dBU REF—  -77 / -87 @ +24dBU REF

So again, as soon as I switch off the Motu 16A the Noise floor increases.
And as originally described, if I connect the Outputs of the RME to a Mackie Passive Knob a rumbling can be heared which I guess is a ground loop.

I also noticed, that the Noisefloor of the Analog Input changes from -97dBU to -44 if my Mac goes to sleep and is connected via USB.

I tried touching my gear (also my SPL Compressor and Vitalizer), but couldn't really detect any static. I also have a old Apogee Rosetta AD and never had this Problem with any of my gear. Do be honest I don't know a lot about electronics, but it still seems like the ADE-2 is causing the issue an not my other gear.

all my gear is just plugged into separate powersocket. I don't really know what connected to Ground means, my Dangerous 2-Bus, SPL Vitalizer, SPL Kultube and Motu 16A are just connected to their powersupplies.

Thanks for your help!

Re: Noisefloor on the Display Meter

anybody? What do I have to do erase this ground loop?

10 (edited by KaiS 2020-05-18 23:23:08)

Re: Noisefloor on the Display Meter

dbot wrote:

... No Analog Inputs connected to the RME => -100 / -99 @ +4dBU REF — -111 / -112 @ +24dbU REF...

... I don't really know what connected to Ground means ...

These figures tell that your ADI-2 Pro is OK.
"connected to Ground" basicly means a PSU's mains connector has a 3-prong plug of any kind, opposed to only 2 prongs (metal parts).


If I follow the description of what you got:
this setup is only usable with fully balanced interconnects, too many ground points for a clean unbalanced signal chain.


• So, first, make sure that every interconnection is fully balanced with XLR connectors and really balanced cables (2 wires + shield inside each cable).

•  Check if the speaker's amp's power cords have a three prong or Schuko connector. Depending on the region you live in, the power cord's ground connector might look different.
Unlikely: but if the power plugs have only two connectors (= ungrounded) this would be an important information.



If the cabling is OK:
The only way to find the cause for the ground loop related hum that, following your description, obviously exists:
disconnecting everything except the speaker's amp.


Then replug one thing at a time, until you get hum,
• starting with the Mackie Big Knob.
• RME ADI-2 Pro.
• Then the USB connection.
At this time only the powered speakers should have a ground connection.
There should be no ground loop and no hum.


•  Now plug one device at a time, starting with the one that is meant to work closest to the ADI-2 Pro.

Once the hum reappears you located the cause for the problem.
• Recheck if these cables are really balanced, see above.
• Have a look if there is a ground lift switch on the device, if yes try to change its position.
• Try temporarly remove Mackie Big Knob and use ADI-2 Pro for level control.



I cannot give more recommendation for a solution at this point, first we have to find the exact reason for the hum.

I suspect Mackie Big Knob destroys the symetry of the balanced signal.
Doing a continous, passive, balanced (symetrical) level control would need an extremly precise 4-way potentiometer - unlikely to have at this price point.
If my suspicion turns out true, either skip the Big Knob (ADI-2 Pro can perfectly replace it) or test the "Mackie Big Knob Studio" that's active and might work better.