Of course there is no directionality in AC signals. But we need labels for two signal terminals, Send & Return are common labels, so is Flow & Return. I like them better than Plus & Minus. I try to keep the word 'ground' out of most conversations, because it often causes confusion. The same labels should apply to both unbalanced and balanced circuits, do you have any label suggestions?
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How about High & Low?
Well I do much prefer + and - to flow and return or send and return myself fwiw. I know what you mean about ground, but most hifi is single ended so one side of the signal is normally "grounded". I have kit where there are switches to connect signal "ground" to chassis "ground" or to separate them. But I am old and used to the old terminology.