" . .but is a GREAT tool for checking for out of phase audio . " which is what Spot? - Guess too difficult to answer on a "text" based Forum. Would like to know though.

Grazie

What he's referring to is having the same audio in the left and right channels but out of phase (one inverted relative to the other). It'll sound just fine on a stereo system but the out of phase component can't be heard on a mono system.

You can build this easily yourself.

Take say a voice recording. Drop it into a Vegas audio track, select Right only, pan it hard left and set tarck gain to -6. Duplicate to another track and pan that hard right, again at -6 and also check Invert.

Still sounds fine although the bottom end might get a little thin. Swtch to mono, nothing, not a squeak!

Now for a real surprise, add another track of nice stereo music, set track for suitable level. Sounds fine in stereo but the voice disappears when heard in mono!

Why is this so scarey? Well most broadcast systems have out of phase alarms except you've added some nice correctly phased stereo music so the things don't go off and at the station all sounds pretty much OK unless they're monitoring in mono. Except those with mono TVs hear no narration.

So you might think you had to do a bit of work to make this happen, right?
Well it can happen all too easily. Some pro gear has minipin plugs that carry balanced audio. Plug them into the stereo sockets on your camera and guess what, sure you get audio on both channels, out of phase audio!

That's why you should always do a final check in mono.
Other things can happen also. Two mics can pickup much the same signal but delayed, delay = phase difference = cancellation at certain frequencies when added. You don't hear this in stereo if one mic feeds one channel and the other mic the other channel but mix it to mono and ooops, big dips in the response.

Bob.

Thanks Bob. G

Thanks for the help, Spot and farss. I admit I'm still a little confused about how problems like this occur. It happened to me when I made a dvd and played it back on a TV that seemed to be stereo, but actually had the same mono track played on both of its speakers. Took me hours to figure out that was the problem.
Then I took some advice and the next time tried using that down mix thing. What I was checking was a couple sounds in the film that are on only 1 channel of a stereo track, so they sound like they are coming from the right side only when played in stereo. This is what I want. I have since gotten rid of my mono tv and was concerned that these sounds wouldn't be audible at all when played on a mono tv, so I tried the downmix to mono. It then played the audio on both speakers, so I figure I'm okay. Right?

Yes.
If you've only got a sound in only one channel then it'l be fine in a mono mixdown.
It's where you've got a sound in both channels that you need to be careful. Speech in usualy in the centre (both channels) and is pretty important as well so it's the one to really watch out for.
Bob.

Very cool. Thank you again, farss!

One small thing you can always do, is process all dialog in Mono, regardless of what recorded it. It's a Safety net in most situations.