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Background story

I recorded a live event, the sound came from the audio guy through a balanced XLR to 3.5mm cable.

Issue

When watching the recording I get extremely quiet and distorted audio.

Issue pointers

I was able to figure out that if I silence either right or left side the audio sounds normal.

I was also able to figure out the issue only happens on devices with only one speaker. Most probably this is related to silencing one side.

Something is telling me this is related to that fact I used a balanced cable, something to the sense the audio is canceled out by the two opposite signals, and that's why it works when I disable the signal from one side.

What is interesting though, I recorded multiple events with the same cable with other audio people, I only have the issue with one audio guy's output.

Questions

I'm trying to figure out what actually happened here?
What do I need to tell the audio guy in the future to prevent it from happening again?
And last how can I fix the current recording it should play on any device correctly?

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1 Answer 1

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Guess one
It wasn't a balanced signal. It was stereo, with one side phase flipped. Bad wiring, confusion of information, you may never know. Balanced mono needs 3 wires, so does regular unbalanced stereo.

The potential fix is to open it in an audio editor, then re-flip the phase of one side. I don't know whether something freeware such as Audacity has this facility, but that's your fix.

The classic symptom of phase reversal is that when summed to mono the signal will cancel out - giving silence if the source was mono, & reduced volume in centrally-panned elements if it was actually stereo.

Late edit

Guess two
It was actually balanced & you treated it as stereo.
Fix would be almost the same - either flip one side or discard one side, as they are otherwise identical.

I'm still tempted towards guess one, as guess two should always sum to zero… total silence.

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  • When I wrote balanced I meant the wire was balanced. It seems indeed it is phase reversal as the sound is almost completely silent. I had to set VLC to 200% sound to slightly hear anything, and event that sounded like squiggles.
    – Yeahish
    Nov 26, 2020 at 22:24
  • Guess two seems more likely, a balanced mono XLR signal was fed to an unbalanced stereo 3.5mm input. If an audio editor can't flip the phase of one side, just select a side, use it as mono and discard the other side. To avoid this in future see if you can get an unbalanced feed or connect the XLR feed through a balun like this and record in mono.
    – Graham Nye
    Nov 27, 2020 at 2:29
  • After further clarification from the OP as to how much gain is needed to hear it, I'm with guess two… too.
    – Tetsujin
    Nov 27, 2020 at 19:48
  • 1
    Audacity does have the ability to flip the phase of a channel. Note in the Usage Examples box that you have to split a stereo track into two mono channels then flip one channel. More information on splitting and re-combining channels here.
    – Graham Nye
    Nov 27, 2020 at 21:55

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