School me on ground for audio

Hello.
I really struggle to understand the concept of ground in audio, how come some ground can be tied together, but other need to be kept separated in the same amplifier
(I am not talking about the obvious digital vs analog ground).
Also why it's better to star ground sometime, but sometime it's better to daisy chain...but most importantly, how do you choose ?

I understand the concept of ground loops, and how they need to be kept small to prevent radiations, or act like antennas.

What I don't understand is : should ground be "classed together" by current.
Or should they tied together following the signal path ? (for example from the input connector daisy-chained until the bridge rectifier).
How to ground multiple PSU (+-15V, 350VB+, Negative Bias, heaters, and relay psu in the SAME amp) for the cleanest ground ?

My question(s) is idiot, unclear and probably badly formulated. But It's just that I am so lost, that I can't even understand how to grasp this concept to formulate it correctly.

Can you also recommend me some readings on "grounding for audio" ?
Or some complete schematic of 2 channel amps with full grounding, that are "perfect" grounding.

I have read a lot of the forum and this :
- http://www.valvewizard.co.uk/Grounding.pdf


EDIT ; you can skip the chassis ground, it has to be connected to the earth, and no current flows in it except under fault conditions.
"And the circuit will be connected to chassis at some point since this ensures the amplifier’s working voltages are properly defined with respect to zero volts, and that the chassis acts as a shield against electric fields. (Merlin Blencowe Designing Valve Preamps for Guitar and bass )"
 
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The problem with ground lines is they can sometimes carry heavy currents.
Given a wire or pcb track is a resistor then changing currents put a changing voltage on wire. These voltages then get amplified by the amplifier and produce hum.
Pre amps tend not to have big currents so arent as prone as power amplifiers.

If its high/medium AC current star ground it.
 
Star earthing is a method of avoiding large currents producing a voltage drop across an 'apparent' S/C, eg. an earth wire, but whose resistance is significant under high current conditions, which then may appear in series with an I/P to a sensitive stage.


Do not draw large currents through an earth path which is also a part of a sensitive stage.


IME loops are to be avoided, but sometimes unavoidable, and I have experienced, albeit infrequently, a better result with them than without.
 
Grounding is much easier at RF as simple shielded compartments are efficient faraday cages at those frequencies, and with feed-through capacitors its possible to prevent signal currents getting onto any DC connections be it ground or supply or whatever.

Audio signals cannot be contained by a few mm of metal (except perhaps for mu-metal), and there are no feed-through capacitors suitable for 20Hz, so signal currents (or distorted versions thereof) have to flow on the ground and supply wiring, meaning there's a signal voltage difference between sections of the system whatever you do.

Differential balanced signals are the best way to cure the problem, but star grounding is a good first step.