I have compared digital streams from Spotify Hifi, Qobuz, Tidal and Deezer with my own CD rips (dbpower with checksum verification). I run these through MasVis (Swedish Audio Society software to analyze mastering quality and more) to do a course check that masters are the same. They usually are, because I have selected albums that are a bit “obscure”, where risk of remasters are lower. Of course I don’t pick MQAs and HiRes albums. Then I run selected tracks through Delta Wave. Result so fas has been 100% bit identical, regardless of service.
To investigate if the player client is doing some funky DSP, I continued with a not so scientific test, but still. I used an iPhone 10 as platform for Tidal, Qobus and Spotify apps. All playing CD quality. I used Roon app as reference for the CD rip. I can’t get the digital stream out here, so I used a Focusrite Scarlett 2i2 to capture the analog signal. The AD converted tracks were run through DeltaWave. Again, as far as one can tell from analog rips, they were identical. Not bit perfect, of course, but close enough. No level difference. No apparent EQ.
This was done a few month ago, and I haven’t done any more research into this with different platforms, as I regard it as a non issue. With that said and done, there is still the issue of how different services differentiate themselves with different masters. If you like what HiRes or MQA is doing to the sound, go for it. Don’t expect Redbook CDDA, to sound different, though! On that note, analyzing and comparing Redbook and HiRes releases of the same album from Qobuz, I have seen a trend that new releases, originally made for HiRes, usually looks better. A bit more headroom and DR. The opposite can be said about re-issues of old albums, now in glorious HiRes. More mastering engineers should just sit on their hands….