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Author Topic: Cleaning It Up: Methods For Controlling Low-Frequency Energy In The Mix  (Read 75 times)

M. Erik Matlock

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Cleaning It Up: Methods For Controlling Low-Frequency Energy In The Mix
Considering the implications and merits of high-pass filters and aux-fed subwoofers as the main defensive strategies.
By Michael Lawrence • December 4, 2018

Recently, a colleague and I were working on a show in a highly reverberant space. Although we only had a few vocal microphones on stage, the room was an acoustic challenge, with a really nasty 80 Hz mode that rang like a bell for more than 2 seconds.

I asked my colleague if he was driving the system’s subwoofer via an aux bus, and he replied that he wasn’t, but that he was using high-pass filtering on the mic inputs. This prompted a discussion as to whether the two methods are equally effective at cleaning up the low end of a mix.

First, let’s define the issue.

A quick look with a spectrum analyzer will confirm that there is often a significant amount of sub-100 Hz signal content picked up by vocal mics on stage. This low-frequency energy consists of vocal pops and plosives, wind rumble, stage noise, traffic noise, handling noise, HVAC noise, and other annoyances.

In all but a few specific situations, this LF energy is unwanted clutter, usually manifesting as an annoying rumble from the subwoofers. The “booms” associated with vocal pops are typically the worst offenders – on plosive peaks, the energy between 60 and 80 Hz can actually exceed the level of the desired in-band vocal content if left uncorrected.

Obviously the optimal solution is to use the right microphone, and several models exist that are designed specifically for these types of problems. However, as is often the case, this was a “this is what we have to work with” situation...

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