• Registered: 2012-03-30
  • Posts: 8

Topic: Fireface Uc Noise Floor Issues

hi folks,

i bought few days ago a fireface uc for measurement purpose (System tuning using SATLIVE). after i installed the drivers and stuff i noticed that one of the two mic preamps, was making strange noises, land you could see also this in the meter of the totalmix. channel one was about -99 dBFS and channel two -80. Moreover if you turned the rotary encoder to adjust the gain, you could listen audible bumps. (everything routing the channel to the c.room and listening to it through sony MDR 7506). So i returned the unit to the local dealer and they gave me a new one. So after that i as corius in figuring out the noise floor of all the 8 analog input. i went through DIGICHECK and put the bottom of global meter about -120 (RME specs gives the analog noise floor -110 dB RMS unwheighted). i noticed the 2 microphones input are steady -112 dB, but the other inputs ( and particularly 3 and 4) have the strange pulsing stuff, oscillating with the meter bar in RMS mode between -110 and -100. this stuff is pretty lo frequency, in fact i checked it against the DIGICHECK spectrum analyzer and what actually pulses is the 25 hz band. and also if you engage the RLB  w filter (basicly an HPF) the noise stuff disappear. Can you guys tell me something about the reason of this meter fluctuation, ...is it normal or not?? did you encounter this in your interfaces as well? consider that it is audible only setting the channel fader at + 6 and cranking up the c room master.

thanks Massimo

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

anyone experiencing with this problem??

3 Reply by MC

  • MC
  • MC
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  • From: Germany/Thailand
  • Registered: 2007-04-06
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Re: Fireface Uc Noise Floor Issues

The input's mic chip is defective. Exchange the unit.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

i changed the unit once and now the mic inputs does not bump anymore, however i saw in the digicheck that the other inputs ( the 6 remaining line inputs) pulse, but this is in the -100 dB FS range, what i would like to know is if is possible that all the 6 line inputs are defective(!!) or if it is normal, and is a kind of tolerance.

thanks MAssimo

  • Jeff
  • Jeff
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  • Registered: 2007-05-21
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Re: Fireface Uc Noise Floor Issues

This is normal, you are just seeing the noise floor of the A/D stage.

Regards,
Jeff Petersen
Synthax Inc.

Jeff's Website

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

yes but you think is normal that the mic preamps are steady at -110 dB and the line inputs oscillate @ a certain rate between -110 and -100?

if you experience is nornal that's ok, otherwise my interface has a problem. the fact is that this establish the noise floor of my measurement rig..that's why i'm really concerned about it, and that's why i bought an expensive interface instead of a cheaper one.

thanks Massimo

  • From: Germany
  • Registered: 2007-04-10
  • Posts: 9,782

Re: Fireface Uc Noise Floor Issues

A certain fluctuation is normal. You could record the signal and amplify it. If it is a steady noise with no other signal components, everything is fine.


Regards
Daniel Fuchs
RME

Regards
Daniel Fuchs
RME

RME Support's Website

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

the noise is not such steady, i recorded it through record feature of the digicheck. And i think is only audible with the fader of the output channel @ +6 and the control room fader @ 0dB ( so is not that loud...!!) and seems like little bump of pink noise. but those bumps look like to fluctuate on the meter in LF rate fashion. and looking at the spectrum analyzer the bump seems to be in the 25 hz frequency band. infact if you engage the RLB Weighting filter it disappear.

sorry if i look to be maniacal, but my attitude is tho measure equipment, so addicted i am to measure in particular the equipment i should work with...

thanks Massimo

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

http://youtu.be/C8ZcAUTaQ9g

this is a video (without audio) of what i'm talkin about see the description for details, and note the big bump at 25 sec.

PS sorry for the focus, the video is made on the fly with my cellphone

10 Reply by MC

  • MC
  • MC
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  • Registered: 2007-04-06
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Re: Fireface Uc Noise Floor Issues

44 or 48 kHz with nothing connected to the UC (except USB and the PS) should have a steady RMS value of -112 (1/2), -108 (3/4), and -112 (rest, +3 dB not active). Check the external PS first, then the unit. The behavior in the video is not normal.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

thanks matthias, i have already change one time the interface because in the first i got from the shop mic preamp number 2 was having the problems. this time all the other input seems to behave strange. Is it possible to receive 2times 2 defected units??

however what i have to check in the power supply??

how have i eventually to behave if the problem is in the unit??

have i to go to the dealer another time and ask him to substitute the interface fore a second time??

http://youtu.be/C8ZcAUTaQ9g

12 Reply by MC

  • MC
  • MC
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  • From: Germany/Thailand
  • Registered: 2007-04-06
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Re: Fireface Uc Noise Floor Issues

Just use a different power supply. Sometimes they start failing. After that please contact your dealer again.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2012-03-30
  • Posts: 8

Re: Fireface Uc Noise Floor Issues

Hi Matthias, i've been to the italian dealer MIDIWARE in rome and we opened another pair of interface, testing them on the Apple setup that they have. Exactly the same problem. I changed my interface with one that has a little less bumping effect..so it seems that it is the whole lot that they have that is defekt. however, in unacking and testing the unit @ home i found another issue, when i start software playback and send it to output 1-2, i experience crosstalk (so i think it's called) on analog input 8!! in practice what i playback on output 1-2 comes back in analog input 8, more or less 10 dB for a 0 dB fader playback. Basicly it seems that in one way or another, those line input are not the same quality as the microphone input circuitry...how can we solve the problem?? if it can help the serial number of the interface i actually own is 23386365

i will post videos ASAP

Wait for your reply

Massimo