Out of phase (issues)

[radiothis!]

The students at the college station I advise re-wiring the signal chain between the board and the tx this summer. This including adding a switch in the signal change that allows switching between control rooms (say Studio A is down for repairs, you can turn a knob and switch to Studio B). Problem is, now the station appears to be out of phase.

Any tips on how to troubleshoot this issue without tearing the place apart? And frankly: I don't know how to fix an out of phase signal. Just switch the pos/neg/ground around?

ck.

 

[TomT]

Yes. Get a portable--mono--radio. Feed something mono into the program line. Does your audio sound weak? You have the phase flipped on one feed.

Another clue is available on your stereo generator/audio processor if you have metering of the L-R signal. With a mono feed, you should be able to "null out" the L-R signal by adjusting the input level of one channel. If you can't do this,(on some multi-band processors it is difficult to get an exact null) but more importantly, the meter shows considerable audio level, you have a phase shift.

To get rid of it you simply switch polarity on one input. But since you are hearing this only when you switch studios, you need to check each studio to see if the outputs are wired correctly.

Most folks use single pair shielded audio cable, red and black wires, by convention, the black wire goes to the (-) output, the (+) has the red. If someone was careless about wiring the console outputs, it is easy to flip one pair and create your phase shift. Some folks like to use 4 wire cable with two individually shielded pairs, black and red; white and green. This is where your phase shift can come in--installer "A" uses white/green for left, with the white connected to the (+) output; installer "B" uses the red/black for left, then connects the green wire to the right (+) (which also switches channels!).

Doesn't matter which is "correct," but it is important that whatever wiring scheme is used that it be consistent.

My bet is you will find the flipped wire in your studio switch.

 

[rrsounds]

Yes. Get a portable--mono--radio. Feed something mono into the program line. Does your audio sound weak? You have the phase flipped on one feed.

Another clue is available on your stereo generator/audio processor if you have metering of the L-R signal. With a mono feed, you should be able to "null out" the L-R signal by adjusting the input level of one channel. If you can't do this,(on some multi-band processors it is difficult to get an exact null) but more importantly, the meter shows considerable audio level, you have a phase shift.

To get rid of it you simply switch polarity on one input. But since you are hearing this only when you switch studios, you need to check each studio to see if the outputs are wired correctly.

Most folks use single pair shielded audio cable, red and black wires, by convention, the black wire goes to the (-) output, the (+) has the red. If someone was careless about wiring the console outputs, it is easy to flip one pair and create your phase shift. Some folks like to use 4 wire cable with two individually shielded pairs, black and red; white and green. This is where your phase shift can come in--installer "A" uses white/green for left, with the white connected to the (+) output; installer "B" uses the red/black for left, then connects the green wire to the right (+) (which also switches channels!).

Doesn't matter which is "correct," but it is important that whatever wiring scheme is used that it be consistent.

My bet is you will find the flipped wire in your studio switch.

Yeah, what he said.

I would just add that this is the kind of thing that could easily be 'fixed' in the wrong place, only to rear its head again later.

Don't just arbitrarily flip the phase; follow the entire path to find out exactly where the mix-up occurs and fix it there.

Kind Regards,
David

 

[TomT]

Amen. As I noted, it is entirely possible to have both a flipped phase AND left and right channels flipped. On some recordings (especially those that just used two mikes, and weren't multi-tracked mastered), this can sound "weird" even if both channels are phased right.

Side Note: You can buy a book of little number labels down at Lowe's (look in electrical); they are about $8. As you trace out the wiring, stick a number on each end, and write down what the wire does (e.g. Wire #1-Studio A console out left to studio switch, Wire #15, fieldhouse line in,..etc.). Your successor (s) will thank for this.