Roon and ultra-highres flac files

I’ve recently been doing some work with offline upsampling software that I modified to push the boundaries of upsampling and create highres flac files to play with Roon (using a sinc resampler with up to 1 billion taps). My DAC, along with many newer DACs, supports sample rates up to 768/24 but I soon realised that the flac container had a limit of 655kHz for its sample rate. I recently created a patch for the libflac code to support sample rates up to 1MHz which would not alter the flac container format at all. Hopefully it will be included in some form in the mainline flac code:

The best part of it is that the existing reference decoder library works seamlessly with it already. That means that my Roon supports these new flacs out of the box. It has allowed me to push the boundaries of my digital installation, and I’ve since moved all my DSP into Roon since it supports native sample rate convolution files, and I created one for every multiple of 44/48 up to 768, and made it far more complex than was achievable with a separate hardware solution. Here’s a screenshot of it in action, along with the insane convolution I use.

Thanks Roon for providing just the right tool for my insane setup. This runs on a separate roon server and I use a roon bridge locally to talk to my DAC and there is a continuous 50Mbit stream coming over the lan to use it without any issues.


I think the how is beyond my understanding but I wouldbe interested in why you are doing this, is it just because you can or is it because you hear specific improvement?
I don’t upsample so don’t really understand what it is for , so assume complete ignorance and vague stupidity in any answers :slight_smile:

For sound quality improvements. The vast majority of DACs oversample internally and the more you upsampe, the less they oversample, and if you do the upsampling on a PC you can shift the effects of the antialiasing filter of the DAC out of the audible range as well. The “ideal” sinc filter is infinitely long but the longer the filter is, the longer the latency on playback, and the more the processing power and memory required. Doing it in advance on a PC means there’s no latency on playback.

1 Like

Thanks I think I understand most of that. Antialiasing I need to go look up.

Upsampling sounds worse using my RME DAC it was quite noticable when I let Roon upsample to max pcm.

Roon’s upsampling is very simple so I’m not surprised. That’s the whole point of my approach - I use an upsampling that is so computationally complex that it would be impossible to do it on the fly.

1 Like

Nice work Con…

Does this FLAC encoder/decoder also work with SoX if built correctly?

1 Like

Yes. It’s just the encoder part of the flac library that needs updating. Sox works with this without needing to be rebuilt since it dynamically loads the flac library.

1 Like

Very nice… Will have to try it out over the next few days… With this and a few tweaks to SoX we have a nice, free, upsampling solution… Again, well done!!!

That’s because the AKM DAC chip in the RME is in reality a DSD chip. Please 1) use Roon DSP to convert everything to DSD256 and 2) set the RME to DSD Direct mode. Enjoy!