• From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Topic: Understanding the importance and function of clock over ADAT / SPDIF

Hey there,

essentially I have a Digiface with a few extra ADAT / SPDIF connections not in use, so I thought that rather than connecting an HDMI audio extractor to my Fireface UC via the analog input connections and then sending it to the Digiface over ADAT, I would just plug the HDMI audio extractor directly into my Digiface via an optical cable. However, I can't seem to get the extractor to output over optical with a 44.1kHz sample rate (seems to be locked at 48kHz). Because of this, I can see in the MADIface Series Settings panel that the input is constantly alternating between "Lock" and "Sync".

I mean just based on the documentation for the extractor, stating "Audio sample rates up to 192kHZ" in regards to the optical output, I would think that I could get it to output at a 44.1kHz sample rate. But I guess it may also depend on what's providing it with the signal? I've got a PS4 Pro and a Nintendo Switch connected to it, so maybe they're the cause of the 48kHz signal? I don't really expect anyone to have definitive answers to those questions as these are products that aren't made by RME, and I've already messaged the company directly asking if there is some way to force 44.1kHz output. Though at the same time, I wouldn't be at all surprised if someone here knew the answer to these questions as they may be common knowledge. This is the HDMI audio extractor I'm using:
https://jtechdigital.com/product/18g-4k … extractor/

Unfortunately, I can't permanently set the internal clock of the Digiface to 48kHz because I have other devices connected that are locked at 44.1kHz. But even ignoring that, I always assumed that that there would be some sort of blaringly obvious issue when connecting multiple digital sources with varying sample rates to one interface. However, I can't seem to perceive any changes when I alternate the internal sample rate of the Digiface between 48kHz (to match the HDMI audio extractor) and 44.1kHz (to match everything else). I would think that I'd hear some sort of difference whether that be a degradation in quality, or some weird speed up / slow down in time when monitoring a source connected via SPDIF that has different sample rate than the internal one / other connected devices.

Clearly I don't fully understand what's going on here and would appreciate any information that can help me get a better grip on the situation.

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD
  • From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Re: Understanding the importance and function of clock over ADAT / SPDIF

I understand that the above post was a bit of a long read and therefore daunting, let me try and simplify my question without all the context.

I have an HDMI audio extractor that has an optical output that is locked at a 48kHz sample rate, I have another Bluetooth audio receiver with optical output locked at a 44.1kHz sample rate. I have two open optical inputs on my Digiface USB and would like to connect the two above devices to said inputs, problem being that they have different sample rates. Though after connecting both of these devices to the Digiface and setting the internal sample rate of the Digiface to 44.1 kHz / clock source to "Internal", I can't seem to detect a problem with the 48kHz HDMI audio extractor despite the sample rate differential.

Shouldn't I be hearing the audio artifacting (pops / clicks) or stretching since it's a different sample rate? Is the interface somehow compensating for the sample rate differential? Are there situations where it is "acceptable" to connect digital devices with different sample rates to one RME interface?

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD
  • vinark
  • DAW Mastermind
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  • Registered: 2009-06-05
  • Posts: 2,640

Re: Understanding the importance and function of clock over ADAT / SPDIF

Is it for listening or recording? If listening acceptable is what sounds acceptable to you. For recording if it works it works except it should not so not sure what is happening. Afaik digiface has no sample rate conversion.

Vincent, Amsterdam
https://soundcloud.com/thesecretworld
Babyface pro fs, HDSP9652+ADI-8AE, HDSP9632
  • From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Re: Understanding the importance and function of clock over ADAT / SPDIF

vinark wrote:

Is it for listening or recording? If listening acceptable is what sounds acceptable to you. For recording if it works it works except it should not so not sure what is happening. Afaik digiface has no sample rate conversion.

I was in the process of making a short video comparing the audio being recording with optical piped directly into the Digiface at 48kHz (HDMI extractor > Digiface) and the audio indirectly piped into the Digiface via digital to analog to digital at 44.1kHz (HDMI extractor > digital to analog converter > Fireface UC > Digiface), as to demonstrate the lack of a difference. But there is in-fact an audible difference, it's subtle but it's there. I was using a Nintendo Switch to conduct the test and I think the compressed game audio help to mask the difference as infinitesimal.

Alas it would appear I am better off using a digital to analog converter, unless there is a way to force the HDMI audio extractor to output 44.1kHz via EDID emulation or something.

Apologies for the trouble.

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD
  • vinark
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  • Registered: 2009-06-05
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Re: Understanding the importance and function of clock over ADAT / SPDIF

Most video audio is at 48k, so I doubt the edid has the cpu power to convert.

Vincent, Amsterdam
https://soundcloud.com/thesecretworld
Babyface pro fs, HDSP9652+ADI-8AE, HDSP9632
  • From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Re: Understanding the importance and function of clock over ADAT / SPDIF

vinark wrote:

Most video audio is at 48k, so I doubt the edid has the cpu power to convert.

I'm fairly new to "pro" audio devices, but it would seem even when the sample rate of my Digiface match these Bluetooth receivers and HDMI audio extractors that I'm using I still see the input status alternate between sync and lock at times. If I theoretically wanted to keep these signals digital and pipe them into my Digiface as such could I use the RME ADI-192?

Granted I convert the optical outputs to AES.

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD
  • ramses
  • DAW Mastermind
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  • From: UTC+1
  • Registered: 2012-10-14
  • Posts: 12,028

Re: Understanding the importance and function of clock over ADAT / SPDIF

ADI-2 Pro FS has a built-in SRC


PC---44.1kHz---RecordingInterface----------------ADI-2 Pro FS ---> monitor+phones
                           With TMFX                                    +SRC ----------<otherdevice with 48--192 kHz>

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13
  • From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Re: Understanding the importance and function of clock over ADAT / SPDIF

lightbox wrote:

What you need is an asynchronous sample rate converter (or 2 of them). They convert the sample rate and reclock the digital audio stream to the master clock (e.g. provided by the audio interface). A budget option of ASRCs would be the Behringer SRC2496.

But here's the problem: Your audio interface (Digiface USB) doesn't have a Word Clock output to feed the master clock into an ASRC. No luck. smile

The Digiface USB only makes sense for external digital devices that feature ADAT outputs AND inputs and where the input can be used as the external clock source.

The reason I brought up the ADI-192 DD is because I thought it was a digital sample rate converter, is it not? I assumed since it had an ADAT input/output and it was an RME product I could get it to sync with the Digiface.

I also have a Fireface UCX and a Fireface UFX+, so if needed I could get a HDSPe MADI FX and use the MADI and word clock connectors to get everything connected and synced I think. Where I connect the UCX and ADI-192 to the UFX+ Via ADAT and then the UFX+ to the MADI FX via MADI.

Though I don’t need that many channels yet lol, would definitely be preferable if I stuck with the Digiface as my central mixer which is what I’m using it for now, a place to control all my levels in one session of Totalmix.

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD

9 Reply by Ninbura (edited by Ninbura 2020-10-21 17:30:45)

  • From: Utah, USA
  • Registered: 2020-10-08
  • Posts: 100

Re: Understanding the importance and function of clock over ADAT / SPDIF

lightbox wrote:

Yes it is. I wasn't aware that you already own one.
You can use the AES inputs for coax S/PDIF (and the front optical S/PDIF instead of AES1). Your Digiface USB can provide the clock via ADAT. Should work.

But to be honest, I would still recommend the (simpler) analog way. PS4 and Nintendo Switch audio isn't audiophile high end audio anyway, is it?

I don't actually own an ADI-192 DD I was just wondering if it would technically work in this application. The reason I would prefer this route is because my setup is extremely complicated and has hundreds of cables running in every direction, it's pretty difficult to get a non-balanced analog connection to my interfaces without using a ground loop isolator which degrades the frequency response. I could get balanced digital to analog converters, but getting 3 of those with good amps seemingly costs more than getting an ADI-192 DD used which I'm seeing for around $600.

If I could get these 2 HDMI splitters and 1 Bluetooth receiver into my Digiface without ever converting them to analog the only analog connections in my entire audio setup would be the cables running to my speakers, headphones, and mics which seems advantageous.

MADI FX, Fireface UFX+, ADI-648, HDSPe RayDAT, ADI-192 DD