Format Conversion / RAAT

Yes, I didn’t understand what y’all meant by “corner cases,” but I’m feeling better now :wink:


hi David,

If I read your correctly than your view is that my DAC like Linn is also receiving MP3 AAC etc and decompression is done in my DAC.

If so, can you shine a light how upsampling is realised in the Roon core ? can one upsample for example MP3 while leaving it compressed ?
There are so many things we can do in the digital domain !

Well, I don’t have a Linn networked DAC, so I don’t have a way to test, but it’s possible that Roon can be configured to allow the endpoint to handle uncompressing the stream in the case of MP3, FLAC, etc. However, if you add volume leveling or DSP, I’d be astonished if Roon did anything other than send uncompressed PCM to the endpoint…even with protocols like Sqeezebox and Linn. To test this, I’d probably do a quick packet capture and look at the data rate.

Me too.

A first step might be to ask @Hans_Bogaert’s friend to provide a screenshot of the signal path with and without upsampling an mp3 stream.

I’ve asked my friend to do a test and send me the result.

As you can see the MP3 file is converted to 174KHz
He also captured via a short movie the display on his Linn DAC and it still shows MP3
I have no understanding how one can upsample MP3 without decoding
Screenshot 2021-03-19 at 20.35.10
Screenshot 2021-03-19 at 20.35.01
Screenshot 2021-03-19 at 20.35.28

Then be astonished, I think.

The actual option under Squuezebox devices is “Use FLAC compression”. So, if you have DSP enabled, Roon is decompressing the FLAC applying DSP and then re-encoding to send to the Squeezebox. Not sure whether it does this if there is no DSP to be done, but, I wouldn’t be surprised if that was the workflow in that case as well.

Here is a post about this:

As for Linn and its own “protocol” solution, I have no idea and I don’t think Roon has every publicly stated; what it really is nor how it functions. (at least I couldn’t find such a discussion, nor, ever remember reading one).

So, no one really knows except Roon and Linn what Roon is sending the Linn devices. It could be PCM, but, if your friend is showing the original format that is being played by Roon, who knows? It might be sending PCM and that extra information to the Linn box for display purposes.

It’s not receiving MP3 it’s getting pcm , however the original files metadata is what’s sent to a Raat endpoint and likely other streaming devices that Roon can play to. It’s not an indicator of the file format that the DAC streamer is receiving it’s the original container.

I don’t get all the fuss about this. It’s pretty simple logic. File formats have to be converted into pcm for transport via RAAT that’s how Roon works and makes it more compatible with systems that don’t support certain containers such as ALAC. Squeezebox can be with flac or pcm , flac is there for the lower end WiFi machines that have older 2.4ghz wireless that struggle with uncompressed pcm. Linn streaming is an unknown entity but my bet its pcm.

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Exactly it’s just getting the original metadata.

LOL. 8467kbps is not an MP3 bitrate. Something funky seems to be going on here…beyond my understanding, anyway. :slight_smile:

@ipeverywhere Thanks. I actually understood this; I read it slowly though. :blush:

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I have no idea about that, you quoted me but responded to a completely different post. My comment is about Squeezebox. I make no comment about Linn which is what the other comment is discussing.

“Linn” is the first word in your sentence. I don’t think either are RAAT edge cases since neither use the RAAT protocol.

hmm…If so then why do we have different views ?
As long as RAAT is a black box we are at the stage of sharing a personal view.
While some opinions might sound ridiculous and are laughed about perhaps they are indeed true at the end ? At least that’s how it went with people like for example Einstein.

I have been using Roon now for 3 years and in these 3 years I’ve used Auralic, Schitt and Denafrips DAC’s

On all these 3 DAC’s I hear a difference in musicality between
FLAC compressed ( level 5 and above)
Flac 0
This with the same file. That doesn’t make sense as Flac is lossless.

I did my comparison test with a compressed level 5 > flac file that I then decompressed to level 0 and to WAV. That providing me 3 files with the same content for sound comparison.
Multiple people could hear the difference in sound quality.

I started a discussion on this forum why this could be.
The end conclusion of the forum was that I suffered from placebo.
But what if indeed RAAT streams the compressed file to the DAC ? Then decompression has to do be done inside the DAC. Eating processing time and perhaps creating jitter ?
And we all know that jitter is killing

Have you tried converting an already compressed flac file to a lower or 0 compression flac file and throwing that in the test process?

Do the compressed and same converted to uncompressed files sound the same or different to you?

If it sounds different I believe you’re on to something with the processing the internal compression. Something else to think about.
Compression does mess with some stuff but I don’t think a normal flac file will be affected. An mqa file will. You can capture an mqa stream in .wav and it’ll work. You can convert that .wav to normal compression .flac, mqa will work. If you change the compression level of the .flac encoder, mqa won’t work.

DACs cant convert formats they except pcm or dsd only. Only streamers or streaming DACs will convert an audio format. In your case these are DACs only I assume connected to your core so they cannot convert anything it has to be done either by software or operating system before it. If your hearing difference then perhaps seperate the audio output from the core, your DACs likely not doing a great job of isolating noise from the computer side of things. I have not heard any difference on any of my systems with different file formats of the same tracks.

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that’s exactly the process I used.
Creating 3 from the same song 3 different versions to listen to

They sound different to me and to the people ( 3 ) I asked their feedback
The difference between FLAC 0 and WAV was challenging but FLAC 5 was recognised in seconds

Hmmm :thinking:

What is the playback chain for this? All from Roon or allowing the streamers to process them. I am unsure about the processes used here.

I understand but that was not the direction I was going here.
It is more that what I understood that RAAT is PCM transport.
But if we see on the Linn MP3 then is that metadata or is it indeed MP3. and is that Linn specific or is it how RAAT works ?
I started to connected/ related a question I posted a few years ago about FLAC.