• Registered: 2013-07-02
  • Posts: 6

Topic: Digiface USB shows 48kHz clock on optical input from 96kHz converters

I am a happy Digiface USB owner. I previously had a Fireface 800 and Babyface, so I'm very familiar with RME drivers. The issue I am having may be inaccurate clock speed displayed in Fireface USB Settings. Audio is clean, I'm not experiencing any issue with sound.

This mismatch between the converter sample rate and the incoming clock rate shown in Fireface USB Settings occurs with any converters connected to the Digiface that are outputting ADAT format (SPDIF doesn't cause mismatch).

I have tested separately with Apogee AD-16X and Lucid 88192. The converter is set to 96kHz, but the Digiface says it is receiving a 48kHz clock.

In Fireface USB Settings > Clock Source is set to "Optical in 1". Under "Input Status" > "Optical in 1" shows "48kHz ADAT".

I previously had a Mytek Stereo96 ADC that output SPDIF format on its optical output, and as one would expect the Digiface showed it was receiving clock data at the selected sample rate - selecting 96kHz sampling rate on the Mytek was reflected in Fireface USB settings with "Optical in 1" showing "96kHz SPDIF" (if I am recalling correctly).

Any idea if this is a problem?

  • waedi
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

If you switch the clock-source to internal, is it set to 48 ?
Change it to 96, then switch back to clock-source external ADAT1, does it stay at 96 ?
Otherwise I would ignore it unless you hear issues.

M1-Sequoia, Madiface Pro, Digiface USB, Babyface silver and blue

3 Reply by oli77sch (edited by oli77sch 2023-04-25 06:02:15)

  • Registered: 2016-06-14
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

That’s simply a single speed clock setting. In this case the clock signals always stays at 48kHz with audio on sample rates at 48, 96, 192 kHz and at 44.1kHz with audio at 44.1, 88.2, 176.4 kHz.

UCX - FF 400 - Babyface pro - Digiface USB - ADI-2 (original)
Mac mini M1 - Macbook pro - iPad Air2

4 Reply by ramses (edited by ramses 2023-04-25 06:04:39)

  • ramses
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

With ADAT there is no possibility for the recording interface to detect whether port multiplexing is in use or not to get the required higher bandwidth to transfer more audio data for higher sample rates (double and quad speed):

- two ADAT ports (44.1 or 48 kHz) are used to get the required bandwidth for double speed (88.2/96 kHz) and
- four ADAT ports (44.1 or 48 kHz) are used to get the required bandwidth for quad speed (176.4/192 kHz)

Seems as if this information is (sadly) missing in the protocol definition / specs, maybe there is nothing like a protocol header with a few bits left to indicate that somehow.

Reliable detection is possible for 2ch protocols like SPDIF or AES as you mentioned where you have 2ch @44.1-192 kHz.

As long as the clock is synchronized, it's fine. I propose you check DIGIface USB's driver settings (post a screenshot if you like) whether clock through ADAT inputs is in Status "Sync".

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13

5 Reply by oli77sch (edited by oli77sch 2023-04-25 11:02:25)

  • Registered: 2016-06-14
  • Posts: 1,142

Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

ramses wrote:

With ADAT there is no possibility for the recording interface to detect whether port multiplexing is in use or not to get the required higher bandwidth to transfer more audio data for higher sample rates (double and quad speed).

Sorry Ramses, maybe I’m thinking in a completely wrong way, but to me that makes no sense. How would it work then for the ADAT equipped receiving unit (audio interface or standalone converter) to handle the incoming signals right?
EDIT: both my interfaces, Fireface400 and Babyface pro only have one single ADAT input port, but do correctly handle SMUX, so at 96kHz there are only four channels. There must be kind of a 'SMUX bit' in the ADAT stream.

UCX - FF 400 - Babyface pro - Digiface USB - ADI-2 (original)
Mac mini M1 - Macbook pro - iPad Air2
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

If the channel count is reduced, everything is fine. The physical sample rate across ADAT remains at 44/48 and may be displayed as such...

Regards
Daniel Fuchs
RME

RME Support's Website

  • Registered: 2013-07-02
  • Posts: 6

Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

Thanks for the responses! It makes sense that 48kHz is the default clock output over ADAT.

ramses wrote:

As long as the clock is synchronized, it's fine. I propose you check DIGIface USB's driver settings (post a screenshot if you like) whether clock through ADAT inputs is in Status "Sync".

Indeed, sync is solid (thanks RME).

https://skipwave.files.wordpress.com/2023/04/screen-shot-2023-04-25-at-3.48.56-pm.png

https://www.dropbox.com/s/2mujgi2s5epjp … M.png?dl=0

  • Registered: 2013-07-02
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

Strangely it seems the Focusrite Octopre sends 96kHz clock over ADAT.

I did a rehearsal recording last night and after connecting the two cables from the Octopre ADAT outputs to the Digiface USB, looking in Fireface settings showed Sync on Optical in 1 and also showed 96kHz on both Optical In 1 and 2.

Now I’m confused again. Is there a setting in the Apogee and Lucid converters that would enable those to also send 96kHz clock over ADAT?

9 Reply by MC

  • MC
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Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

There is no 96 kHz clock. The Focusrite might support (send) an inofficial 96 kHz SMUX indication (as most RME units do), which then gives a direct readout with that frequency at the RME input. The carrier is still 48 kHz, though.

Regards
Matthias Carstens
RME

MC's Website

  • Registered: 2013-07-02
  • Posts: 6

Re: Digiface USB shows 48kHz clock on optical input from 96kHz converters

MC wrote:

There is no 96 kHz clock. The Focusrite might support (send) an inofficial 96 kHz SMUX indication (as most RME units do), which then gives a direct readout with that frequency at the RME input. The carrier is still 48 kHz, though.

Ah, I see. Thanks for the explanation!