Why Low-End Frequencies Can Kill Your Mix and What to Do About It

Low end frequency problems can plague a mix if they aren’t identified and addressed. In episode 39, I discuss how the low end frequencies can work both positively and negatively. I also discuss how you can control excess low end both on stage and in the sound booth.

Update: Just to be clear, when I talk about mixing the bass and kick drum together around the 80 and 100Hz areas, I’m not talking about rolling off frequencies of one of the instruments.  I’m talking about cutting a narrow area so one instrument can dominate that spot in the mix.

Transcript

(Here’s a rough transcript)

Welcome episode 39 of the behind the mixer podcast, I’m your host, Chris Huff.  If you’re a member of behindthemixer.com and get the regular newsletter, you’ll remember last week I posted up a huge article on strategies for people who were serious about learning church audio production – same can be true, really, for live audio production in general.

In that article, I covered everything from vocal mixing to critiquing your mix to how to keep your ego in check.  What we do has a lot to do with technical matters, creativity, and working with people.

Today, I want to hit a topic that often plagues new audio techs and it’s that of low end frequencies.  There are great sounds created in the low end but we don’t always want them. In some cases, we only want them in some channels.  Already this might seem a little confusing.

Here in Indiana, if you dig deep enough, you hit a layer of the earth we call Indiana clay.  It’s red, firm, and if you add just a bit of water, it becomes pliable enough to make beautiful pottery.  Seems like a great medium for pottery work, right?

However, if you’re trying to plant a garden or put in a tree, that same red clay can be a royal pain as we have to remove it and replace it with fresh top soil, or what most people think of as dirt.

Low end frequencies are like that clay, both useful and annoying.

Low end frequencies tend to run below 250 Hz.  There isn’t a hard and fast rule on where it begins but that’s a good place to start.

Let’s start with what low end frequencies can provide in a mix.  I’d say warmth, energy, and a solid foundation to the music because without enough low end, the mix sounds thin.  But as mentioned, low end frequencies can be equally problematic when it’s someplace we don’t want it.

Now imagine a singer with the drums bleeding through into his microphone.

There’s your good and bad.

When we are mixing audio, we want low end in some channels and not in others.  How we can control that comes in a few areas.

First, let’s look at stage setup.

What enables a good grab of low end frequencies?

We want the low end of drums, bass, and electric guitars. Even acoustic guitars can provide a nice bit of low end energy as the open string of the low E of an acoustic guitar runs around 82 Hz. For that matter, even the open B string is around 246Hz.

You could be getting sounds from these instruments in a variety of ways, such as on-board pickups, amps, and direct sends.

If you aren’t getting the sound direct into the system, then you want to use a close-miking setup.  For example, with a kick drum, you’d want a kick drum mic inside the drum. Or, with an upright bass, I’d place an instrument condenser mic on a stand, close to the strings around the bridge, assuming I can’t use a proper mic like a dpa d:vote 4099.

In the case of stage amps, like guitar and bass amps, you’ve got options.  You could run a line out from the amp if the amp has that functionality and get the sound that way.  Or, you could mic the amplifier up close – the method I prefer.

You want up close miking because you want to capture the low end at the source so you don’t have to have it so loud that it’s broadcasting out for other channels to pick up.  In some cases like guitar amps, you’re still going to get some volume direct from the amp.

The next part of stage setup is musician placement.  I don’t want my singer to be right by the drums. I need to watch for proximity to other microphones meant for other instruments or vocals.

Finally, on the stage, I don’t want my singer to use a microphone that’s going to pick up everything on the stage. Therefore, I’m going to tend toward a cardioid vocal mic that the singer will have right up to their lips.  I don’t want to get into drum shields and the such but I hope you can now see how the stage work can go a long way to keeping the low end frequencies where you want them.

Now that takes us to the work in the sound booth and, at least in the interest of this podcast, I’m going to focus on removing or reducing the low end where necessary.

Remember how i said the vocal microphone needed to have the low end removed when you’ve got the drums in the background.

We want to remove that low end from the vocal channel.  However, it’s not the ONLY low end we want to remove.

When it comes to low end control, we have a few options.  The first might seem the obvious but it’s NOT the first place we want to go.  And I’m talking about the EQ control for the low frequencies.

This control creates an EQ shelf.  That is to say everything below a certain frequency is reduced by the same about.  Commonly, we say everything below that point is rolled off but in reality, it’s not.   With the EQ control for the low EQ, we can control how much the low end frequencies are cut.  For example, 3dB or 12dB or more. Therefore, if you want to reduce, the key word being reduce the low end, you use the EQ control.

However, if you want to remove it completely, you turn to the High pass filter, commonly abbreviated online as HPF.  This applies a significant cut and what I’d call a true rolloff of frequencies below a certain point.

Back to the low end in our singers mic.

By using the high pass filter, I can remove everything below a value, such as 100Hz.  In the case of analog vs digital mixers, analog mixers are usually using a fixed point HPF such as 80 or 100 and digital mixers give you full control.  I have seen analog mixers with a variable HPF but those are rare.

But we’re not done.  Just because the drums are gone, it doesn’t mean I’m done with my low end work.

This is where we get into the other way low end can mess up your mix.  It can remove clarity, cause it to sound muddy, make instruments hard to tell apart. You get the idea.  It’s like a fog settling in over a town – it makes it hard to pick out one building form another.

I might want to reduce some vocal low end or even pick a point in which I only want to cut a thin amount of low end, such as somewhere between the 250 and 350 mark for male vocals to improve clarity.

Reverb

As another tip, watch your reverbs.  When you add reverb to anything, you’re performing an additive process and that could mean even more low end and more muddiness.  With digital consoles, you can EQ your effects busses. We do this at my church by rolling off much of the lows and the highs because they aren’t what we want reverbed, especially the low end.

I also mentioned different instruments that provide low end, such as bass and kick and guitars.  When it comes to mixing these, you need to decide what amount of the low end you want each to have.  For example, you might give the bass 80Hz, the kick 100Hz and the upper areas to the guitar. In doing so, you can cut frequencies from these channels so the others come out or you can boost.  You might even do a little of both.

There is no simple answer to how you should do this as it depends on what frequency signature you’re getting from those instruments.

Consider today’s podcast as a basic low end primer. There’s a lot you can do to improve the low end, such as I just mentioned with the bass and whatnot but the most important work starts with eliminating it form where you don’t want it.

Thanks for joining me on today’s podcast and if you’d like to learn more about mixing, check out my guide, audio essentials for church sound.

Resources:

• Got the Low-End Frequency Blues?
• Audio Essentials for Church Sound

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