1 (edited by FZ 2019-12-08 01:17:24)

Topic: Interference in the analog inputs of the UFX

Hello,

I am a sound designer and work a lot with timestretch and pitching of the audio material I record. That's why I bought a pair of Sennheiser 8020s some time ago, because they work almost linearly in a frequency range from 10 to 60000 Hz. Unfortunately I noticed that there is an interference signal on the input channel 9, if you amplify the signal with some gain. This noise is about -70 dB at 49000 Hz, so it won't matter for most cases. But if I now pitch a signal down into the audible range, this sine peak can cause problems if it suddenly becomes audible at 13 Khz. By the way, these interfering signals occur more intensively on the input channel 12, also in the 4000 Hz range.
My guess is that these are interfering signals caused by the power supply.
Is there a solution to minimize these noises?

2

Re: Interference in the analog inputs of the UFX

Ch9 0dB gain:

https://www.bilder-upload.eu/upload/86f7ab-1575763858.png

3

Re: Interference in the analog inputs of the UFX

Ch9 35dB gain:
https://www.bilder-upload.eu/upload/166355-1575763902.png

4

Re: Interference in the analog inputs of the UFX

Ch12 0dB gain:
https://www.bilder-upload.eu/upload/d162b0-1575764055.png

5

Re: Interference in the analog inputs of the UFX

Ch12 35dB gain:
https://www.bilder-upload.eu/upload/49bb52-1575764118.png

Re: Interference in the analog inputs of the UFX

In almost every case I encountered, this kind of interference was caused by not loading the input with a 200 Ohm resistor.

7

Re: Interference in the analog inputs of the UFX

I Think the MkH 8020 only has a rated impedance of 25 Ohm like most condenser microphones. Does this mean that interference signals will occur if I do not use the preamps with dynamic microphones?

8

Re: Interference in the analog inputs of the UFX

First of all we should clear something basic (IMHO what cyrano tried to say): were your measurements made with open inputs, means nothing connected?

Regards
Matthias Carstens
RME

Re: Interference in the analog inputs of the UFX

I was actually able to get a similar result like FZ at 48kHz with my UFX. I also testet it with my trusty Behringer ADA8200 slaved to the UFX via ADAT wink

With nothing connected to both preamps I get peaks/interference at 3,4kHz , 16,8kHz, 20,3kHz and 23,7kHz on Inputs 11 and 12 of the UFX with 55db of Gain. I get a bit of 20,3 on Input 10 and visually no interference on input 9. The peaks on input 11 and 12 are around 5-7db above the noisefloor in each frequencies range. I do not get any peaks on the Behringer, even when nothing is connected with gain maxed out. The noisefloor is about the same on both units with these gain settings. (-66dbfs peak). I measured both preamps with a test signal into a Beyerdynamic M201 to put out equal level at these settings.

With the M201 connected to the UFX all of these peaks disapear and the noisefloor drops 8db at 10kHz to about -102db (low end rumble in my room make a fullrange peak measurement irrelevant). With the M201 connected to the behringer nothing changes, but the noisefloor drops about 9db at around 10kHz at -103db.

Then I connected a Rode NT5 SDC to both my UFX Input 12 with 55db of Gain and then to one of the Behringer ADA 8200 Mic Inputs with the Gain maxed out.

With both Preamps I get interference at 18,4kHz.

I noticed the level of Interference changes when I change the direction the Rode Mic is facing. This happens with the M201 aswell. After these tests I kind of get the feeling that both FZ and I might be dealing with some kind of HF interference from outside sources, here. But I am no expert in this field.

If this was the case however, I am wondering why the Behringer did not catch anything when nothing was connected.
Both units are directly mounted in a rack together (Don't hate me big_smile ) and share the same poweroutlet with a Brennenstuhl Premium Line Powerstrip.

I would appreciate any knowledge on how to get rid of this.

Ps: I was also kinda shocked to have slightly lower noise in the high frequencies on the Behringer ADA8200. In the case of the Rode NT5, the mic is obviously limiting the SNR. But with the M201, I expected the UFX to be quieter than the Behringer.

10 (edited by FZ 2019-12-10 00:45:00)

Re: Interference in the analog inputs of the UFX

Hello Matthias,
the pictures above are only the preamps without connection.
Here again a couple of pictures with different scenarios:


Channel 12 +35 dB gain without connections:
https://www.bilder-upload.eu/upload/e8be3c-1575932527.png

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Re: Interference in the analog inputs of the UFX

Channel 12 with u87 + Phantom Power +35dB Gain:
https://www.bilder-upload.eu/upload/54c819-1575932890.png

12

Re: Interference in the analog inputs of the UFX

Channel 12 with u87without Phantom Power +35dB Gain:
https://www.bilder-upload.eu/upload/1e719f-1575933004.png

13 (edited by FZ 2019-12-10 00:14:58)

Re: Interference in the analog inputs of the UFX

Channel 9 with MKH8020 + Phantom Power +35dB Gain, 5m away from UFX:
https://www.bilder-upload.eu/upload/cfd282-1575933185.png
Don't pay attention to the grip noise below 20 khz

14

Re: Interference in the analog inputs of the UFX

Channel 9 with MKH8020 + Phantom Power +35dB Gain, 10 cm directed at the power supply of the UFX:
https://www.bilder-upload.eu/upload/eb4e77-1575933384.png

Re: Interference in the analog inputs of the UFX

Get a male XLR plug. Solder a 200 Ohm resistor between pin 2 and 3. Plug into mic preamp input. Then repeat the measurements.

You simply can't measure a high gain mic preamp with open input, or a microphone connected. Depending on the environment, the preamp will pick up RFI or any other noise (like your computer) when the input is open. Instrument inputs are probably even worse, as the impedance is a lot higher (470 k vs 5 k).

And the mic or it's cable might also pick up noise. There could also be a voltage converter producing ultrasonic noise inside the mic. Besides, an MKH is a source of HF noise, as there is a HF circuit inside.

16

Re: Interference in the analog inputs of the UFX

Unfortunately, it is a pity if the noise recorded by the preamp is caused by the built-in parts of the interface. I tested the problem with 5 different RME interfaces in 3 different buildings/studios. Among other things, I only recorded the UFX interface via USB without a computer. A similar situation can be observed everywhere. With the tested Babyface Pro, the noise was the quietest, I assume, because it is supplied by bus power.

17

Re: Interference in the analog inputs of the UFX

Here the Babyface Pro (Bus Powered) 45dB Gain (no mic) for comparison:
https://www.bilder-upload.eu/upload/09adf7-1576077642.png

Re: Interference in the analog inputs of the UFX

useless measurement...

19

Re: Interference in the analog inputs of the UFX

Enlighten us with your insights. Where should the interfering signal come from if I have tested different circuits, rooms, computers and microphones and it is always the same interfering signals that are individually interspersed in the channel?
Why does the signal get louder when I point the microphone at a specific point on the interface?
If anyone can make a reasonable measurement, it's the engineers at RME. Nevertheless, such disturbing noises should not occur in the first place.

20

Re: Interference in the analog inputs of the UFX

With the UFX+, which I borrowed for testing, the problem does not occur. It seems to be a component problem with the UFX I. I'm glad that the problem has disappeared with the new RME generation, but I don't think it's okay that this problem occurs at all, at the price I paid for the device 4 years ago. Even the ADA8200 was not affected by such a problem and we know what the price difference is.