Hearing Comb Filtering (Screencast)

I was so happy when Joe Gilder from www.homestudiocorner.com mentioned phase issues in his recent post about Using Multiple Microphones. Why? Because I had just made this screencast and wondered if anyone would care about learning to recognize comb filtering. See, recording with two microphones often leads to the signal arriving at each microphone at different times. Two signals arriving milliseconds apart creates comb filtering: an ugly sound that will kill the tone of any instrument. It also happens when internal latency issues in your DAW causes two versions of the same signal to playback at slightly different times.

When I first started recording I read about phase issues and comb filtering but I had no idea what it sounded like. This screencast shows you how to create comb filtering effects so you can instantly recognize that evil sound. I worked in ProTools 8, but you should have all the same tools in your DAW of choice.

http://www.youtube.com/watch?v=2QPAFJyVb7U

I would like to add two things that I forgot to mention in the screencast. Often a signal will arrive at two microphones less than a millisecond apart, which can sound worse than the one, two and three millisecond varieties. To hear the effects of that kind of comb filtering, just enter a number less than 44 into the "Samples" portion of the Shift Region Dialog.

Secondly, how can you check for phase issues when recording with two mics? First solo each microphone and get an idea of the tone of each mic individually. Then play them together and listen for comb filtering. Now that you have an idea of what that sounds like, it shouldn't be hard to recognize.

If you hear comb filtering, all is not lost. You should be able to zoom way into both waveforms and carefully line them up so they're in phase again. It might take a few tries, but you'll get it if you use your ears. If the comb filtering arises because of internal routing delays (often caused by effects, parallel compression type techniques, or complex bussing), you may have to use a time adjust plug-in to compensate for the latency between signals. I'm not going to get into how to do that in this post, but you should be able to find tutorials online.

Happy Recording!

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