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Interesting Stuff I Found

Quick System Check

David Snyder

I wanted to find a quick way to confirm channel identification, polarity, and phase for any that I measure. The Audio Tool app has a tool for this, but using it requires a mic with a line-out port and running a cable from the phone or tablet to a free input on the preamp...not always convenient.

This morning, I had an idea for creating a tone in Adobe Audition that is compatible with the phase/polarity function in Audio Tool. Turns out that it was not that difficult. I just needed a 30Hz sawtooth waveform.

I created 2-channel and 5-channel versions that test positive and negative polarity. The negative tests are just to confirm that Audio Tool is working as expected. It should read "Pol ++" for the positive tracks if the system has correct phase and "Pol --" for the negative tracks.

For channel identification, the correct sequence is L, R for the 2ch tracks and L, C, R, Rs, Ls for the 5ch tracks--essentially, clockwise around the room starting with front-left.

To use the tracks, just set "Polarity" to "On" under the "Gener" menu and then switch the display mode to "Specrogram" in Audio Tool. Play the tracks on your system with the phone's mic near the tweeter and watch for "Pol ++" or "Pol --" on the display.

When I ran these tests in our theater, I actually discovered that I had the left surround speaker wired out of phase! It was correct at the speaker end, but I apparently got the leads crossed at the amplifier side the last time I had the system disconnected.

Another interesting thing I found is that the mic in my Samsung Galaxy Note IV is wired out of phase. I get correct readings with a Dayton IMM-6 mic plugged in but opposite readings with the internal mic. Strangely, none of the folks I've talked to on the phone have complained.  :-P

Here's a link to the test files if you'd like to give this a try.

-- David