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i posted a tweet asking about why TRS balanced audio jacks can accept TS unbalanced plugs and have it “just work”, but i had to delete it because i immediately found out why:
TS plug -> TRS jack
(mono signal) T -> T (complement 1)
(ground) S -> R (complement 2)
(ground) S -> S
the noise reduction works like
output = complement₁ - complement₂
because the TS ground gets routed to complement 2, the result becomes basically
output = complement₁ - 0
so It Just Works! yay!
oh and to explain what balanced audio is: on professional audio equipment, you often use a TRS “stereo” jack to carry a “mono” signal as a differential pair. i'm calling the two signals in the pair the “complements”. it is like:
T = original signal
R = inverted signal or 0
S = 0
i'm getting a real kick out of finally understanding this. it seems like this complicated topic and then like… no, it is ridiculously simple and intuitive. it's a very, very simple technology that works super well. the world is so cool
in the balanced audio case btw the equation
output = complement₁ - complement₂
becomes
output = original - -original
output = original + original
output = 2 × original
and indeed, that's how balanced audio systems behave, the signal level is doubled :3
oh and to round it off: why do they do this “balancing” thing? because any noise the cable picks up is assumed to have the same polarity in both copies of the signal, but you've inverted one of your copies, so when you invert it back (subtract it), it should cancel the noise :3
@hikari that is also how error detection for USB 1 and 2 works!
There is a single dataline on two wires, one is polarity inverted
@hikari wait until you find out how the Instrument Landing System works
@whitequark i will have to dig into this later… am i going to find out that they figure out how to create a straightforward analog interference pattern that just magically tells the aircraft how to orient itself?
@hikari yes