• From: Adelaide - Australia
  • Registered: 2007-05-01
  • Posts: 455

Topic: Strange artifacts in Analyzer

Hi all,
I have been noticing some strange behavior with the analyzer for quite some tim now.
Most of my work is broadcast tv advertising here in Australia and I'll often check things out with Digicheck (mainly levels with the 4 bar).
However, I have noticed something unusual with the analyzer with both Digicheck Mac (beta) and Digicheck 5 on my PC. They both seem to be show artifacts on the 25 Hz bar, even when I have a really steep 48db/8ve Linear phase high pass filter on my master bus in LogicPro.

Although I'd not vouch for the reliability of the Logic Multimeter, it is not showing the signal at 25Hz.
Am I crazy, or has anybody else noticed this?

http://img.skitch.com/20090629-g3tqbm9q9xsrcw59xwe5tdn5wn.preview.jpg
Click for full size - Uploaded with plasq's Skitch

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Matt McKenzie-Smith (UFXII, UFX, Babyface) MacStudioUltra OS13.2.1
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mattrixx's Website

2 Reply by MC

  • MC
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  • Registered: 2007-04-06
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Re: Strange artifacts in Analyzer

As written in the online help this is not a 25 Hz bandpass, but a 0 Hz to 28 Hz hicut filter. The problem you see is most probably DC. See Bit Statistics, DC.

Regards
Matthias Carstens
RME

MC's Website

  • From: Adelaide - Australia
  • Registered: 2007-05-01
  • Posts: 455

Re: Strange artifacts in Analyzer

Hi Matthias,
Thanks for responding so quickly. After searching through the online help, I am unable to find any reference to Bit Statistics.
but here's a question.... To use the Spectral Analyser, I have to have the FireFace 800 outputs looped back so that I can use the input feature in the I/O for DigiCheck Mac, so could this DC be introduced at that stage? As it seems that I can't get rid the 'DC' using a DC offset removal plug. Also, if I apply DC offset removal and play a file from Quicktime for example, the 25Hz lumps pop up at random (or at least that's what it look like).
I haven't been able to see anything about bit stats in the Mac version of Digicheck either.

Sorry if this all sounds a bit confusing, but I would love to get to the bottom of this.... not sure whether to be too concerned or not.

Regards,
Matt

----------------
Matt McKenzie-Smith (UFXII, UFX, Babyface) MacStudioUltra OS13.2.1
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mattrixx's Website

4 Reply by MC

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Re: Strange artifacts in Analyzer

Of course, Bit Statistics not yet exists under Mac, sorry. Is this an internal TotalMix Loopback? No DC added then.

Regards
Matthias Carstens
RME

MC's Website

  • From: Adelaide - Australia
  • Registered: 2007-05-01
  • Posts: 455

Re: Strange artifacts in Analyzer

Aha... thanks Matthias... Glad I'm not still looking for it! ;-)

Yes, using internal loopback. Mmm, I wonder where this is coming from then... the DC that is.

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Matt McKenzie-Smith (UFXII, UFX, Babyface) MacStudioUltra OS13.2.1
----------------

mattrixx's Website

  • Registered: 2008-07-14
  • Posts: 8

Re: Strange artifacts in Analyzer

Hi Mattias,
I have the same strange behavior on my PC. Im using a old Digi96/8 PAD under Windows XP. If I use DigiCheck with WaveLab 6, I have the same problem. There is no DC in the materiel and especially when I stop the playback, I see this 25Hz peak. in former versions of Digicheck (something like 2.xx or 3.xx) this didn't exist.

Regards
Markus

Windows 10 Pro 64bit Core i5, 16GB Ram, FirefaceUCX Cubase 10, WaveLab 9.5

7 Reply by MC

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Re: Strange artifacts in Analyzer

No, it's not the same thing. What you see is the last samples of a buffer that are continuously played back. This causes a fixed level display, DC, with random amount, also in other level meters.

The fix is to playback two buffers with digital zero before stopping (while DC still continues to work - multi-client!) - or to ignore this display information.

Regards
Matthias Carstens
RME

MC's Website

  • From: Adelaide - Australia
  • Registered: 2007-05-01
  • Posts: 455

Re: Strange artifacts in Analyzer

Hi Mathias... I must admit, I am still a little confused about all this, even after reading the literature.
The material I am monitoring definitely does not have any DC offset etc in it. However,I still see the artifacts.
Sorry, if I'm missing the point here, but as I mentioned, I am still not clear on this.

regards,
Matt

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Matt McKenzie-Smith (UFXII, UFX, Babyface) MacStudioUltra OS13.2.1
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mattrixx's Website

  • Registered: 2007-10-28
  • Posts: 68

Re: Strange artifacts in Analyzer

You are not alone Matt.Same here.
While i was checking the filter responce in audio leq after lots of sine waves for
the whole spectrum I discovered the same thing.Actually I did it already,but with a sine at 30hz
it is clearer.
Then as Mc said could be a loop back problem.
Then I tried with a pink noise:the problem was still there.
I tried with white noise and no strange behaviour appened.
What does this mean?
Thanks
Alessandro-roma

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Re: Strange artifacts in Analyzer

bug in the algorythme that does FFT.... ?

  • Registered: 2007-05-09
  • Posts: 646

Re: Strange artifacts in Analyzer

Grag38 wrote:

bug in the algorythme that does FFT.... ?

There's no FFT in DIGICheck at all!

12 Reply by Timur Born (edited by Timur 2009-07-30 19:06:32)

  • Registered: 2008-01-01
  • Posts: 3,025

Re: Strange artifacts in Analyzer

I once asked a similiar question (with lots of screenshots) in an older thread. Matthias answer in that thread very much cleared the question for me.

I notice that you have a steep filter on your signal and thus expect nothing to be left down there, but obviously there is something left and because of the 25 Hz band showing *all* it's a bit emphasized on the display. Maybe your filter just isn't as steep/good as you think it should be? wink

First this band is not a bandpass (as the others), but a low pass, so it covers a wider range and thus shows more energy when given the same signal. We added this feature to detect low frequency rumble (when mastering long play records) and DC problems easily. That said it seems the one software indeed produces a high amount of DC, or has a wrong filter architecture around zero to 10 Hz. The display also shows DC errors of older converters very good (like the ones done with early DAT recorders).

As the area below 25 Hz does no include useful information sonically (ideally this one would be empty), having a low pass instead of a bandpass makes a lot of sense (that our competitors did not yet notice...grin...).

Here's the full thread: http://www.rme-audio.de/forum/viewtopic.php?id=3029

13 Reply by MC

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Re: Strange artifacts in Analyzer

Mattrixx,

we reworked the 25 Hz band display in the analyser. It no longer works as low pass, but is a real 25 Hz band pass plus a DC band. This way it works much more as expected than it did before. Effects where the lowest band seemed to be boosted for no reason are gone.

Additionally the Bit Statistics including the RMS and real DC meter is now included. Check it out!

https://archiv.rme-audio.de/download/di … 54_mac.zip

Regards
Matthias Carstens
RME

MC's Website