• From: Oakland, California
  • Registered: 2021-06-21
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Topic: Mysterious Clocking/SRC Behavior on Digiface AES

On my Digiface AES (connected to an M2 Mac mini running MacOS Sonoma), I've got a non-synchronous, 44.1 kHz audio source connected to the RCA SPDIF input and in TotalMix FX I have that input routed to the main output submix (along with other sources).

Mysteriously, even when I've set the sample rate on the Digiface AES to 96 kHz and disabled the SRC on the SPDIF input, the sound coming out of the main monitors is just fine!

Here's a screenshot of the driver settings (showing "Lock" input status on the SPDIF input):

https://www.dropbox.com/scl/fi/f10ecizgpt2bicq5zj6k8/Screenshot-2023-11-16-at-9.43.56-AM.png?rlkey=pu19h84lbhhkhi6zmn4sw4bdl&raw=1

This status is also reflected on the front panel display of the Digiface AES (the input status icon is blinking green when the SRC is disabled but is solid blue when the SRC is enabled for that input).

I can't hear any difference between disabling the SRC and having it active on the SPDIF, but that doesn't make sense--I would expect the sound from a non-sync'd 44.1 kHz source being played through an interface running at 96 kHz to at least have loud clicking artifacts.

Is this possibly a driver bug (such that the SRC is actually active when it says it's not) or is there another reason for this behavior?

Thanks,
Adam

2 Reply by MC

  • MC
  • MC
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  • Registered: 2007-04-06
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Re: Mysterious Clocking/SRC Behavior on Digiface AES

Record that signal (best simple sine wave) and check its waveform. You will see it is heavily distorted - unless the SRC is activated.

The DF AES behaves different to other RME interfaces. Usually already at lock state the digital input signal is muted. In this unit mutes are only executed on signal loss. So small transmission errors that cause usually inaudible errors (SIC) do not cause an  audible drop out. Etc.

It also makes a nice convenience feature, as you can monitor all inputs any time. Just make sure if you want to really use them they are clocked correctly.

Regards
Matthias Carstens
RME

MC's Website

  • From: Oakland, California
  • Registered: 2021-06-21
  • Posts: 50

Re: Mysterious Clocking/SRC Behavior on Digiface AES

Ah, that's very interesting, thanks, Mathias.

Here's a 1 kHz sine waveform with the SRC engaged:

https://www.dropbox.com/scl/fi/tcizspg5xjysjxxurftnr/Screenshot-2023-11-16-at-10.05.01-PM.png?rlkey=3cafvb0weuegj40aq3lnmqcrd&raw=1

And here it is with the SRC disengaged:

https://www.dropbox.com/scl/fi/5iz34e184xt7he5ns4pta/Screenshot-2023-11-16-at-10.05.09-PM.png?rlkey=6kcqntqcap2dxz5bk8ks7mzj6&raw=1

I can definitely hear a little distortion in this particular signal without the SRC but it's a lot less than I was expecting, and with complex signals it's harder to detect. Cool to be able to see it!

4 Reply by MC

  • MC
  • MC
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Re: Mysterious Clocking/SRC Behavior on Digiface AES

I have to correct myself - most of our interfaces behave like that. It is mainly the ADI-2 series where we strictly mute when the sample rate does not match or is only 'lock'.

Regards
Matthias Carstens
RME

MC's Website

  • vinark
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Re: Mysterious Clocking/SRC Behavior on Digiface AES

AdamBier wrote:

Ah, that's very interesting, thanks, Mathias.

Here's a 1 kHz sine waveform with the SRC engaged:

https://www.dropbox.com/scl/fi/tcizspg5xjysjxxurftnr/Screenshot-2023-11-16-at-10.05.01-PM.png?rlkey=3cafvb0weuegj40aq3lnmqcrd&raw=1

And here it is with the SRC disengaged:

https://www.dropbox.com/scl/fi/5iz34e184xt7he5ns4pta/Screenshot-2023-11-16-at-10.05.09-PM.png?rlkey=6kcqntqcap2dxz5bk8ks7mzj6&raw=1

I can definitely hear a little distortion in this particular signal without the SRC but it's a lot less than I was expecting, and with complex signals it's harder to detect. Cool to be able to see it!

Very interesting, thank you for posting the waveforms and your experiences!

Vincent, Amsterdam
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