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RME babyface optical in too loud (or DVD players optical out too loud?)?

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RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Guitarking » Sat Oct 20, 2018 7:03 pm

I have my DVD player connected via optical out to the optical in of my RME Babyface, but it overloads/clips. Is my RME too sensitive or is the DVDplayer's output too loud (JVC XVS42 DVD player)? How to adjust?
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby James Perrett » Sat Oct 20, 2018 8:30 pm

Is the DVD player sending out a plain stereo SPDIF signal or is it Dolby/DTS encoded? Is the Babyface input set to the right format?
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Wonks » Sun Oct 21, 2018 9:38 am

They may be totally different formats. Isn't the RME expecting an ADAT optical input?
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Hugh Robjohns » Sun Oct 21, 2018 1:29 pm

Guitarking wrote:I have my DVD player connected via optical out to the optical in of my RME Babyface, but it overloads/clips.

That's not possible. You have a digital interface there, and a digital interface can only transfer numbers. There is no sensitivity issue. The numbers coming out of the DVd player are received by the interface. Job done.

The only thing that can actually overload or clip is the D-A converter that you're using to monitor the signal. So something is happening after the DVDs signal has been received at the interface, and before it leaves it for your speakers!

Now it is possible for a perfectly legitimate digital signal to cause peak overloads when converted through a phenomena known as inter-sample peaks, but that is extremely unlikely to be the case when watching normal commercial DVDs because the peak and average levels tend to be well controlled.

The first thing to check is whether the sound on the DVD is actually recorded with the clipping/distortion. Not all TV sound is perfect, and it's a lot easier to hear flaws on legacy recordings now that it was when they were first broadcast! So check the disc on a different playback system and check out some different discs to find out if the problem applies to all discs on this specific system.

Much more likely, though, is that you have inadvertently introduced some digital gain into the signal path, and that's what is causing your problem. I'd take a close look at the settings of the RME's TotalMix app for starters,, and then check the signal path gain structure of any other software you're using (including the OS or any video playback software). It would also be worth checking which drivers are being used and if they are up to date.

It could be an issue with Dolby Digital or DTS encoded signals on the DVDs as they are transferred as a raw data signal and need to be separately decoded before auditioning. So again, check your DVD viewing/decoding software and the gain structure of the decoded output.

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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby James Perrett » Sun Oct 21, 2018 2:22 pm

Wonks wrote:They may be totally different formats. Isn't the RME expecting an ADAT optical input?

RME usually allow you to choose between ADAT and S/PDIF on at least one of the optical inputs.
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Wonks » Sun Oct 21, 2018 2:25 pm

The DVD player certainly won't be outputting in ADAT format. What has the OP set the optical input format up as?
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Hugh Robjohns » Sun Oct 21, 2018 3:46 pm

S/PDIF and ADAT use the same optical connection format but they are completely incompatible as a data format. So if the interface is set up for the wrong one it simply won't work at all -- it will be mute -- rather than work but with peak distortion.
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby Guitarking » Thu Oct 25, 2018 7:36 pm

Thank you all!
The RME is set for optical in.
I can't find any knob to adjust input with digital systems in the Totalmix Window.
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Re: RME babyface optical in too loud (or DVD players optical out too loud?)?

Postby CS70 » Fri Oct 26, 2018 10:25 am

Guitarking wrote:Thank you all!
The RME is set for optical in.
I can't find any knob to adjust input with digital systems in the Totalmix Window.

Hm.. a digital link simply sends over the samples - one by one and at the level they are. They are numbers. Don't know what a DVD uses and have no time to look it up, but if it's the same CD audio, it uses 16bit numbers and that means numbers between 0 and 65535 (included), and that's about it. All the rest is synchronization and other meta-information which the receiver either understands, or doesn't. If the source and target devices synch, the numbers will pass as they are, if they don't, they will be mangled beyond recognition and what you hear from the target device won't have any resemblance with what's sent by the source.

I use my ancient Multiface with the current TotalMix, and the SPDIF in and out do have faders. Can it be that you've hidden them? It's easy to do in TotalMix and then forget about it :)

Assuming they're set at unity, the distortion must come from something else - either before or after. The SPDIF in must be routed to an analog out (and the RME does the DA job) , so
most likely you're unwittingly overdriving the D/A converter or the analog output, or the physical speaker driver itself - easy to do if you are listening on headphones for example. Alternatively there could be something off with the hardware but it sounds odd.

A bad optical cable might introduce some random change in the numbers - which then is translated to noise - but it seems odd that it does it consistently... but if you have another cable it can also be worth trying after you've checked the software faders.
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