In every case I have seen (and I've seen a lot) the signals on pins 2 & 3 of an XLR are identical but polarity inverted from each other. If you look at a typical microphone specification, they would say something like "Positive pressure on diaphragm produces positive voltage on pin 2 with respect to pin 3." (A quote from the Shure SM58 spec.) So, as long as the balanced signal isn't being faked, you can safely take the signal between ground and pin 2, and ignore pin 3. It's not like positive pressure goes to pin 2 and negative pressure to pin 3, or anything weird like that.
The purpose of having both wires is because noise induced on the wire is (mostly) identical on both wires, and a balanced receiver recovers the DIFFERENCE between the two wires, thus the noise cancels out completely, since it's the same on each wire making the difference zero.
I haven't seen any cases where "balanced"signals are faked, not even with the old Behringer mixers (these were low budget products). Doing so would eliminate the noise protection, but since the receiver is looking at the difference, it will still recover a signal with one end stuck at zero. That's why it's okay to plug a single-ended unbalanced source into a balanced input. (I'm talking about those connectors that have 1/4" TRS balanced inputs - it's okay to use a TS plug in them). But doing so removes the noise protection. You could also have a driver for one side burn out, and not notice for a long time, as they only symptoms would be a 6dB drop in signal level and maybe some noise if you were in an environment with long enough wires for noise to be noticeable in a line level signal.
Actual case of this: I have a Kurzweil PC3le plugged into my Yamaha TF5 in my home studio. Using TS cables, It worked fine but I was getting noise (it's a longish run from the other side of the room). The Kurzweil has balanced outputs, so I switched to TRS cables, and the noise predictably went way.
I've seen a lot both because of the years I spent as the lead audio developer for Avid Media Composer, because because of decades of experience in live sound for small churches, where we use a lot of "iffy" equipment. My formal education is in electrical engineering.
Another real example. Connecting an unbalanced signal to a balanced input, you can often get really good results by connecting the unbalanced source to pins 2 and 3 of tine input, and leaving the "X" ground disconnected altogether. I do this at church to get iPad audio back to the FOH mixer, and I still get the noise cancellation effect of the balanced input, because it's the same noise on both wires, although only once contains signal. Sounds great, and doesn't have the low-pass degradation caused by cheap direct boxes :-)
The purpose of having both wires is because noise induced on the wire is (mostly) identical on both wires, and a balanced receiver recovers the DIFFERENCE between the two wires, thus the noise cancels out completely, since it's the same on each wire making the difference zero.
I haven't seen any cases where "balanced"signals are faked, not even with the old Behringer mixers (these were low budget products). Doing so would eliminate the noise protection, but since the receiver is looking at the difference, it will still recover a signal with one end stuck at zero. That's why it's okay to plug a single-ended unbalanced source into a balanced input. (I'm talking about those connectors that have 1/4" TRS balanced inputs - it's okay to use a TS plug in them). But doing so removes the noise protection. You could also have a driver for one side burn out, and not notice for a long time, as they only symptoms would be a 6dB drop in signal level and maybe some noise if you were in an environment with long enough wires for noise to be noticeable in a line level signal.
Actual case of this: I have a Kurzweil PC3le plugged into my Yamaha TF5 in my home studio. Using TS cables, It worked fine but I was getting noise (it's a longish run from the other side of the room). The Kurzweil has balanced outputs, so I switched to TRS cables, and the noise predictably went way.
I've seen a lot both because of the years I spent as the lead audio developer for Avid Media Composer, because because of decades of experience in live sound for small churches, where we use a lot of "iffy" equipment. My formal education is in electrical engineering.
Another real example. Connecting an unbalanced signal to a balanced input, you can often get really good results by connecting the unbalanced source to pins 2 and 3 of tine input, and leaving the "X" ground disconnected altogether. I do this at church to get iPad audio back to the FOH mixer, and I still get the noise cancellation effect of the balanced input, because it's the same noise on both wires, although only once contains signal. Sounds great, and doesn't have the low-pass degradation caused by cheap direct boxes :-)
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