Any time two channels on a console have the exact same input, with their EQ settings slightly different to achieve some tonal options, phase shift of various degrees starts to occur. This adversely affects the combined tone. It’s not vital to understand why, but it is important to remember that it does indeed happen and is why the kick drum can actually sound worse when the two differently EQ’d channels are combined.

The same goes with utilizing HPF for EQ tailoring on one mic but not the other. If the “inside” mic channel is EQ’d to be more “snappy” by rolling up the HPF and adding some high end, and there’s no HPF on the other channel, some serious phase abnormalities can occur. So, what can we do about it? Here we go:

Polarity (ø) Reverse Button. As noted earlier, using the polarity reverse button on a console to try to correct a badly combined pair of inputs has been the most widely used method for decades. Long before digital consoles came along with added features on the input channel strip, the “flip” was the only option for a fix. But keep in mind you’ll only get two results when employing the polarity reverse feature: result 1 and result 2.

Using the previous example of an inside kick drum mic (such as a Shure BETA 91) and an outside mic (such as a Telefunken M82), the general approach is to EQ each channel to sound the best it can by itself and then add them together. But if the combined sound is “weird” and low-end has disappeared, you would probably flip the polarity and try again. If it sounds better but not 100 percent of the way there, you’d then work some more with the EQ and then move on to the snare because you’re out of options.

Input Delay. Now that many consoles offer an input channel delay feature, there’s a much better chance of coming up with a great combined sound when using multiple channels. As a rule, I start by delaying the input that I believe to be “closest” to the input source (in the case of mics). For example, when combining two kick drum mics, I apply some delay to the inside mic because it’s physically closer to the beater head than the outside mic.

One can certainly experiment with adding delay to one input or the other to see which is better, but in general the goal is to delay the input closest to the source. This isn’t always obvious – if you’re combining a bass DI with a bass mic on the cabinet, one might assume the DI signal arrives first but this isn’t always the case. Use your best judgement and then start experimenting.

As you apply delay to one input, remember that EQ and HPF affect the combined result to a significant degree, so when changing either of these settings for one or both input sources, re-check the delay time after tweaking. When EQing the inside kick mic, mute it and move on to EQing the outside mic so both sound as good as possible on their own, then try them together. If it’s not perfect, try a little bit of delay on the inside mic until it comes together. Usually 2 to 4 milliseconds (ms) of delay will do the trick.

“Tuning” With Input Delay. You may find as you’re making minor changes to the input delay on one input that the combined sound moves and shifts in pitch. This is because the time offset changes the peaks and nulls of the comb filter, altering the frequencies that sum together as well as the frequencies that “cancel” as the delay is applied.

With that is mind, try this “next level” trick the next time you combine two kick or guitar inputs. Adjust the delay time of one input up and down just a bit while listening to both. With kick drum, the “sweet spot” of combined low-end frequencies will move up and down from 30 Hz to 120 Hz or so, and you can “tune” the low end to the desired frequency range. If you like a thumping kick at around 60 Hz, tweak that input delay until you get it singing or tweak it some more to get 40 Hz to be the roundest sounding region.

With multiple guitar inputs, try adjusting one of the delay times just a little and you’ll feel the midrange morph. When you’ve attained the biggest, fattest sound – you’re there. And don’t forget the good ol’ pan knob in this experimental process. Two “like” inputs that are just a little bit “unlike” in tone but are panned further left and right can sound really cool together, just avoid the center if they’re not time-aligned to work together perfectly.

Or, going back to where we started – you could just put one mic on everything and lower your stress!