1 Topic by NoisyNarrowBandDevice (edited by NoisyNarrowBandDevice 2022-02-15 10:49:41)

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Topic: Digicheck showing >25khz Signals on 44.1 Material

My BFP is set to 96Khz and I frequently see signals exciting the 25k, 32k and 40k bands in the Spectral Analyser in Digicheck. Most material is encoded at 44.1, some at 48 and in many cases I am playing back MP3 files.

There should be no signal above 22k espc. with MP3s. Why is the Spectral Analyser showing something in the ultrasonic bands - are these aliasing artefacts? 

Playback is via iTunes or Apple Music or whatever they call it these days. Also via the filesystem's quicklook.

  • vinark
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Re: Digicheck showing >25khz Signals on 44.1 Material

Interesting, how are you playing back 44k files with the BF at 96k? Upsampling needs an anti aliasing filter just like a DA converter. So what is doing the upsampling is not filtering correctly it seems.

Vincent, Amsterdam
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Re: Digicheck showing >25khz Signals on 44.1 Material

The BFP is set as the audio output device in Audio MIDI Setup. Sampling rate is set in Fireface USB Settings and changes accordingly in Audio MIDI Setup.

Not sure where decode and SRC is happening but I guess handled by MacOS. If so the BFP only converts what's coming down the USB pipe.

  • vinark
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Re: Digicheck showing >25khz Signals on 44.1 Material

If it sounds at normal speed, this would mean Apple is not doing the upsampling properly. Did you try a player with upsampling included in the software? I don´t know of any on mac, but I am sure they exist.

Vincent, Amsterdam
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Re: Digicheck showing >25khz Signals on 44.1 Material

Didn't try an upsampling player but will if I find an Audionirvana or Amara trial.

Sound is normal so it must be something in the upsampling process or some other reason for the presence of ultrasonics.

Perhaps somebody from RME could chime in here?!

6 Reply by sbcrikey (edited by sbcrikey 2022-02-15 23:29:51)

  • Registered: 2021-12-30
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Re: Digicheck showing >25khz Signals on 44.1 Material

the few times I've actually used 96k and Digicheck, I had to close and reopen it to get the display to work correctly. Have you tried that?

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Re: Digicheck showing >25khz Signals on 44.1 Material

sbcrikey wrote:

the few times I've actually used 96k and Digicheck, I had to close and reopen it to get the display to work correctly. Have you tried that?

Nope will do! Thx!

Haven't seen any issues beyond the ultrasonics though. And the movement of the bars correlate with the music flow, i.e. 25k slightly excited when a crash cymbal is hit etc.

8 Reply by MC

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Re: Digicheck showing >25khz Signals on 44.1 Material

I doubt that is the Crash Cymbal. The filters have limited separation, so when 16 kHz goes up 20 kHz will follow with a few 'LEDs' distance. Same with all bands. With that in mind I am pretty sure the 25 kHz you see is the higher level crosstalk of the lower band. And there is nothing at 25 kHz.

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Matthias Carstens
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Re: Digicheck showing >25khz Signals on 44.1 Material

Thx Matthias.

Which filters are you referring to? The filters in Spectral Analyser?

10 Reply by MC

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Re: Digicheck showing >25khz Signals on 44.1 Material

Of course. Use a 1 kHz sine then you will see what I mean.

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Matthias Carstens
RME

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