Help my understanding of Digital Volume levels

[McFly]

Hello Friends,

So I'm currently using an RME ADI2 DAC, which will probably be with my until I die or RME release a new model. What I can't get my head around is the digital input seems to 'clip' when using any iOS device or iMac. That is, when the RME display is set to show "Pre-FX", the signal is (on most songs) exceeding 0.0 and displaying an 'OVR' level.

So I mainly use Spotify for music at the desk, but it also (rarely) happens coming from web browsers playing radio streams and YouTube videos. I get the same overload condition playing Spotify from my iPad to the RME DAC. To test this I plugged a CD player into the unit and not once ever did a CD pass the 0.0 input level, albeit I only tried a few with varying genres.

Now my understanding was that digital volume level output from a computer, if set to max in the application and the O.S. (iMac reports no OS volume control when ADI2 DAC is connected i.e. is passing full signal), would never pass a theoretical "ceiling" and thus show 0.0 on the RME DAC input meters no matter what. My temporary solution is to lower the applications volume control, but my understanding here is that I am now losing 'bit-perfect' (yes I know it's only Spotify/internet streams but that's a topic for another debate).

To sum up;
-Some songs/internet streams behave and never exceed 0.0 when iMac -> USB -> DAC.
-Most songs/radio streams don't behave, and drive into overload when iMac -> USB -> DAC
-CD player never overloads/exceeds 0.0. CD Player -> Coax S/PDIF -> DAC
-The RME does not audibly distort even in OVR condition, is this because there is internal "Digital Headroom"? (The reason I say this is when I tried iMac Spotify to a miniDSP SHD Studio at 100% Spotify volume, I got HORRIBLE distortion, and this was with no EQ or Dirac enabled in the miniDSP)
-I tried, and have had the same result (digital clipping) from a Raspberry Pi running RopieeeXL Spotify -> miniDSP SHD studio. Have not yet tried into RME DAC.
-I am aware of intersample peaks when upsampling, but Spotify is 44.1khz and the DAC is showing 44.1khz so there should be no upsamping. Is the Mac re-sampling if thats such a thing?

Any help much appreciate.

 

[suttondesign]

my 2011 backup imac at my home office has a bad sound card and cannot pass a clean digital signal from any software or the core. my mac minis (4) pass pristine digital to various dacs, including rme, topping, and matrix.

 

[Blumlein 88]

I wonder if spotify is doing resampling? That might explain the behaviour as spotify is the common link to regular overs. It certainly is the case some web streams and youtube is resampled.

 

[McFly]

Upon doing more tinkering, I have been unable to get the input to overload by inserting the miniDSP SHD studio between the iMac and DAC. So Spotify iMac - USB - miniDSP studio shd (at full pass through 0.0, no EQ) - coax S/PDIF - RME ADI2 DAC. Does this mean there is a problem with the Mac sound driver, or is the miniDSP seeing the digital overload and truncating it? I can't be certain of the latter, as the 'Studio resamples all incoming digital to 96khz and outputs at 96khz. The RME' confirms this.

 

[Blumlein 88]

Do you have a way of recording the digital stream being played? That is what you really need to find out where the issue is coming from.

 

[McFly]

Can the RME DAC do that? Ill look into that

 

[Mnyb]

Can you rip a CD and play with some application on the Mac ?

 

[bennetng]

Now my understanding was that digital volume level output from a computer, if set to max in the application and the O.S. (iMac reports no OS volume control when ADI2 DAC is connected i.e. is passing full signal), would never pass a theoretical "ceiling"

Not necessarily. Search "Realize that even if we don't use any DSP features" in this article and read until the end.
https://archimago.blogspot.com/2019/06/guest-post-why-we-should-use-software.html

 

[renaudrenaud]

Not necessarily. Search "Realize that even if we don't use any DSP features" in this article and read until the end.
https://archimago.blogspot.com/2019/06/guest-post-why-we-should-use-software.html

Many many thanks for this link.

 

[Blumlein 88]

Not necessarily. Search "Realize that even if we don't use any DSP features" in this article and read until the end.
https://archimago.blogspot.com/2019/06/guest-post-why-we-should-use-software.html

You did a good job on that article in examining the issues involved.

 

[Blumlein 88]

Can the RME DAC do that? Ill look into that

I don't think the RME DAC can record the digital stream.

 

[maverickronin]

I don't think the RME DAC can record the digital stream.

It can record the S/PDIF coax.

 

[Joachim Herbert]

1.) Any processing active on the ADI-2 DAC?
2.) Perform a factory reset, just to be sure: Press Encoder 1 and encoder 2 and the VOL key, then turn on the unit.
3.) Which Input: USB or sp/dif? If the latter, try USB.

 

[Blumlein 88]

It can record the S/PDIF coax.

Ah, so it does. I just looked over the manual, and you can record the optical or coax inputs as you play them.

Also, if the OP hasn't done so, the Digicheck software from RME can be downloaded, and it should help with finding the true level of streams.

 

[Blumlein 88]

So you could record the SPDIF stream from the Mini DSP by running it into the RME. Then you can take that recorded stream and run it from your computer thru the RME and see if it then overloads. Possibly there is a better way, but that occurs to me right off hand.

 

[q3cpma]

Hello Friends,
-I am aware of intersample peaks when upsampling, but Spotify is 44.1khz and the DAC is showing 44.1khz so there should be no upsamping. Is the Mac re-sampling if thats such a thing?

It's not only during upsampling, but also during DA conversion, at least if talking about analog clipping. Which is why true peak exists for replaygain.

 

[McFly]

Can you rip a CD and play with some application on the Mac ?

Excellent, cant believe I didn't think of it. So I blew the dust off a USB CD drive and plugged into the iMac. Playing the same song that on Spotify would cause the DAC to overload, does not overload when played from the CD through the 'Music (formally iTunes?)' app to the DAC. Stays at -0.1 input level.

Get this. Spotify can play local files too. So ripped that CD to .WAV, loaded into spotify, played it and ... max level -0.1 input AKA not overloading.
Navigate to the stream of the exact same song (not a remaster, not an edit) and what do we get .. Overload. For those that are interested the album I am using is DAMN by Kendrick Lamar, but there are plenty more examples I can give. My music tastes are not up for discussion.

This leads me to believe the spotify stream is forced to be louder/clip for some reason. And when I was putting the miniDSP in the chain, it was truncating the clipping so the output to the DAC was corrected i.e. lowered to not overload the DAC input.


Now to get a Tidal Subscription.. and maybe cancel the spotify supscription after all these years. Shame on you Spotify. Could be jumping the gun here...

 

[McFly]

Another silly question - Is there software that can capture and record the digital stream before it leaves the USB outlet on the iMac, or does this all have to be done by hardware external to the iMac? I'm assuming the latter due to my limited knowledge of the way the usb bridge works on the motherboard. For now I will box on with recording the SPDIF coax out of the miniDSP and try to understand what I find.

 

[maverickronin]

Another silly question - Is there software that can capture and record the digital stream before it leaves the USB outlet on the iMac, or does this all have to be done by hardware external to the iMac? I'm assuming the latter due to my limited knowledge of the way the usb bridge works on the motherboard. For now I will box on with recording the SPDIF coax out of the miniDSP and try to understand what I find.

Software like that does exist. If you were on Windows I'd recommend Virtual Audio Cable. A quick google found similar seeming things for Mac, but I've got idea which ones are any good.

A Mac user might be able to give you a specific recommendation.

 

[McFly]

Ah, so it does. I just looked over the manual, and you can record the optical or coax inputs as you play them.

Also, if the OP hasn't done so, the Digicheck software from RME can be downloaded, and it should help with finding the true level of streams.

I'm working on getting a windows laptop to check, Digicheck looks like it could be very useful, but no Catalina support

EDIT: I get none of the spotify overload issues on a windows machine. I now suspect this is something to do with the iMac/iOS and RME relationship... as my iMac and iPad overload the RME's digital input. Might even be a Catalina thing.. but can I be bothered installing Mojave..