I do have to tell you though that dedicated ccts do indeed often use separate neutrals
Agree, a true dedicated circuit does not share a neutral with other circuits.. Therein a multiwire branch circuit.
Multiwire branch circuits are not considered, IMO, as true dedicated circuits. If a 3 wire multiwire branch circuit is installed to feed an audio system, that’s not two 120V dedicated circuits, imo, that’s two 120V separate circuits.
Multiwire branch circuits, as a rule, are not recommended for feeding audio systems that are connected together by interconnects. When more than one branch circuit is used to feed audio equipment, that is connected together by interconnects, the circuits should be fed from the same Line from the same electrical panel. Therein residential split phase 120/240V all from L1 or all from L2. Not from both L1 and L2 though.
Also as you know only the unbalanced load of L1 to neut and L2 to neut returns on the shared neutral to the source. As you know the balanced load(s) of L1 and L2 are in series with one another and are being fed by 240V. So the garbage, hash, being fed back out on the power cord of a digital piece of equipment using a Switched Mode Power Supply will be dumped, fed, in series into the power cord of the power transformer of a analog preamp or power amp. Noise? You are better feeding all your equipment from one 120V dedicated branch circuit.
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From an old 2019 post of mine.
Why install all dedicated circuits on the same Line, Leg?
"Less than 300 microamps of ground loop current can cause hum as it flows in an unbalanced audio interconnect cable. However, harmonics of 60Hz that are generated from lighting dimmers or switch-mode power supplies sound like Buzzz mixed with a bit of Hummm and are more easily coupled by even smaller currents. Harmonics can add together when equipment is powered from different phases, so clearly there is an advantage to specifying same-phase electrical service to power the electronics systems in most cases....
Any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference....
Power conditioners do not solve any of these common problems: Cross phase coupling (doubles hums & buzzes) .... What actually does solve them: Same phase power.
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Split Single Phase electrical service is most commonly found in residences and smaller commercial buildings, and is commonly used to feed AV equipment. One key advantage that single phase has over three phase is that while harmonic currents are still present, it is not possible for the �triplen� components to add in the neutral. In addition, use of split single phase can result in at least a 6dB reduction in noise floor as compared to three phase if the capacitances of the connected equipment are relatively well balanced. However, any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference."
http://www.exactpower.com/elite/assets/pdfs/theTRUTH.pdf