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RME User Forum → DIGICheck → offset
Hello,
I'm recording samples taken by the analog inputs 7 and 8 and using DIGICheck but keep getting signals whose graphic display is defective in relation with or the reference point. What can I do to amend this problem? I am absolutely lost. How can I control the offset?
Thanks for your help.
Lorena.-
Please be more specific - which graphic display are you referring to exactly? Could you provide a screenshot?
Regards
Daniel Fuchs
RME
Hi,
Thanks for your help. I'm working with PRAAT for speech analysis. I attach a screenshot.
Thanks again.
Lorena.-
It's the audio software that builds the graphic display, this is not related to the fact that you used Digicheck for recording. I don't think we can be of any help here. What "reference point" are you referring to?
Regards
Daniel Fuchs
RME
Thanks for your reply. I'm trying to take advantage of this fantastic resource as much as I can. The reference point I mention in my previous post is the “0 line” or axis. Because of the offset, I would like to test, through a control software for amplifier or preamplifier, a way to compensate this bias. Could you tell me where or how can I find that control in the software? I mean control software for a preamp.
Thank you very much.
Lorena Ham. -
The graphics show a low frequency modulation of the recorded audio. To find out where this originates you will have to examine the whole recording chain.
Hi,
I'm working in a linguistic lab. We've done all kinds of tests. We recorded with various programs (DIGICheck, PRAAT, Sound Fordge). We tested the connectors and connections. The cable with which we work is Monster (shielded) XLR.
Now, according to the manufacturer of the pair of microphones (Avenson STO-2), I need to work with the preamp. I know the problem is not the FireFace. In fact, I recorded using a Tascam and through m-audio interface and, although the signal is more stable, the offset problem persists. What I want to achieve by using FireFace is precisely control the bias by using preamp software. However, I have not been able to find it in the FireFace applications and I need your help on this. Do I have the ability to compensate offset through the FireFace, or have to get a separate device, a preamp?
Thanks again,
Lorena Ham.-
Bias or offset is a static thing, means not changing. You can not 'compensate' a low frequency modulation, only remove it by applying a DC filter or low cut filter.. This of course might rermove audible low freqeuncy components. You use which Fireface?
Thank you MC. I'm using FireFace 800.
Not sure what happened to my answer, tried to post here.
1) Technically this is not a DC offset. What you see is a low frequency "hum".
2) Best is if you can remove that hum. If not possibly you will need to remove it with a high-pass filter.
3) Most probable cause from my experience is 50 or 60 Hertz mains interference created by a ground loop. Do try to assess what frequence the hum has.
To remove ground loops can be frustrating. You need to consider each and every part in the chain from mics to computer to see how and when it occurs. Typically be either removing thing by thing or by disconnecting all cables and the connect one at a time.
My suggesting is to first assess whether it really is a ground loop.
1) connect one mic directly to the FF800 mic input using your XLR-XLR cable.
2) Make sure neither the metal outside of the mic or the metal outside of the connector on the cable touches anything metallic
3) If you record using a laptop, disconnect the power supply to the laptop and run a recording using only battery
If the "hum" disappears here, you can start to connect one thing at a time to see when the problem reappears.
Most probable cause in my experience is
a) laptop power supplies
b) the connection between preamp and FF800 since you have two cables (can create ground loop) as well as possibly both connected to a grounded mains output.
In b) the solution is to modify the cables between mic preamp and FF800. A short descriptiion is to disconnect shell from pin 1 and disconnect shield from both pin 1 and shell on one side of the cable.
// Gunnar
On second thought, there is one more possibility worth checking.
The frequency of the signal looks like it is around 4 to 6 Hertz.
A typical source for this kind of signal when it persists all the time is air conditioning in the room.
Do try at a time when air conditioning is off or in a different building.
// gunnar
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