How to upgrade to low latency kernel on Pi OS(Debian bookworm)?

[agent_kith]

That is a very bold claim!

It is not easy to tell the difference between my Pi4 (Mercury V2 Streamer) with a real time time kernel and my NUC with the Ubuntu real time kernel. Maybe the NUC is slightly ahead.  Both are using the same linear power supply, CPUset and convolution DSP.  

In my setup, the Pi 4 CAN produce very good music quality!

I think your Mercury V2 is CM4 based? CM4 (and hopefully future CM5) based boards are slightly different. I'm thinking/hoping this player of yours has a crystal (usually encased in a metal can) on a board somewhere. Some even have 2..

You kind of need that to generate a regular tick so that the Pi can be slaved to it (Master clock). Without that, the tick will be generated by some chip or via software (there's also a tickless mode) I actually forgot which is better now. :/ Problem with using software to keep time is the time can "drift" when the CPU is busy. That drift back and forth is considered jitter and may "smear" audio, in the sense you seem to lose a tiny bit of that pin point precision (Just a guess as I can't really confirm this).

Pi on it's own do not have a crystal. But I'm almost certain you can provide a different (hopefully better) clocksource for the Pi (via one of the GPIO).. However I'm no longer in the DIY scene so havn't really keep myself up to that. It's just easier with CM4 as you plug the CM4 daughterboard onto some main board, which should have all the components required for a good audio system.

Pi unit on it's own will not be a high end player. But if using it for ambient background music for work, etc? it'll still be good.. It's like using BT wireless headphones, all those AptX and so on, they all sound terrible. But we still use wireless because it's convenient.