I have dual RCA cables that I'm trying to plug into a mixer using RCA to TRS adaptors. They don't sound good, there is cancelation, and I know I need RCA to TS adaptors--they are in the mail.

My question is--what exactly is happening with the signal from a wiring perspective? I understand that the TRS adaptor is expecting red, black, and shield, but the RCA is only supplying two of those.

I want to know exactly WHY it sounds bad.

* UPDATE / EDIT: I am now using RCA to TS adapters and the sound is fixed -- as expected. *

It's a Mackie mixer and the line in is balanced / unbalanced. I assume that the line in will expect TRS to be balanced, and TS to be unbalanced. I am assuming that the RCA cable's signal is doubled and put into both the tip and the ring. The mixer is treating Tip and Ring as a balanced signal, but it's not polarity-reversed like a balanced signal, instead it is a duplicate signal, causing cancelation.

The rest, I'm not sure if it's relevant but: It starts with an iPod, TRS headphone out carrying unbalanced stereo, split with a Y adapter to dual RCA, dual RCA cables are both adapted with a RCA to headphone TRS, which are each adapted from headphone TRS to 1/4" TRS before going into the mixer line in. It doesn't matter if I put them into the stereo pair channels or mono channels, it doesn't matter if I only plug in one of the cables or both.

  • 1
    Could the TRS input be expecting balanced audio, not stereo?
    – Linuxios
    Nov 3 '16 at 16:55

Your question is missing several critical details, but making a wild guess, the most common cause of symptoms as you describe is opposite-phase CANCELLATION. Because a "TRS" (presumably BALANCED) input has an active positive (Tip) and negative (Ring) input, when you put two unbalanced signals into it (Left channel on Tip) and Right channel on Ring), you end up with Left MINUS Right. So you are hearing only the DIFFERENCE between Left and Right. That that typically sounds quite strange.

  • Yes, so it sounds like a stereo to balanced mono connection. Tut tut... ;¬]
    – Marc W
    Nov 4 '16 at 21:14

I know what I am talking about. I have been dealing with audio issues like this for over 50 years.

The line input on your Mackie mixer (model number and specific input not identified) is probably TRS balanced. That means it expects the +audio to appear on the Tip of the plug, and the -audio to appear on the Ring, with the Sleeve as the ground/shield.

Audio coming out of an RCA connector is by definition, unbalanced. Because there are only two terminals on an RCA, the inside (audio) pin and the outside (shield/ground).

When you plug your Left unbalanced signal into the Tip of your TRS balanced input, the audio likely goes through just fine. So far, so good. HOWEVER when you connect your Right channel unbalanced signal to the Ring of your TRS balanced input, the Mackie will SUBTRACT the Right signal from the Left signal and leave you with the DIFFERENCE signal, which will typically sound strange, horrible or even unusable.

You never really know how those commercial adapter plugs and cables are wired unless they provide a diagram and/or your actually measure them.

The flip-side of this problem is when people take a balanced monaural microphone and plug it in to the unbalanced Left and Right channels of their camcorder. When you listen to the resulting recording through the air (or on headphones, etc.) is sounds perhaps a little strange, but OK. But when they drop it into their video editing software and combine the Left and Right channels, they suffer from near or total cancellation because they have the same monaural signal in opposite phase on Left vs. Right. This is a VERY COMMON problem with amateurs who are just getting into video production and use the wrong cable for their microphone to their camcorder.

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