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Sweeping the Frequencies for Precise EQing


If I there's one plug-in that's the audio equivalent to a Swiss Army knife, it would have to be the EQ plug-in. From subtle corrections to drastic sound design changes, you can use an EQ plug-in for an almost infinite list of tasks. In this tutorial, I will show you one such technique, called Sweeping the Frequencies, that can give you surgical-like precision when EQing and notch filtering a sound source to better fit in your mix.

Looking at the Sound

When using an EQ—which is short for Equalizer—you are essentially given control over a sound source’s volume. But instead of having an overall global affect, like when using the master gain on a channel strip, you can turn the volume up or down on specific frequency bands independent of the other frequencies. 

You can quite literally filter which frequency bands you want to turn up or down and affect only the ones you want, which is where the term filter comes from. Most DAWs will come with at least one EQ plug-in, and most commonly a type of EQ called a Parametric EQ.

To use the frequency sweep technique you will need to use a Parametric EQ plug-in, because this specific type of EQ haves three features that are needed:

The channel EQ that ships with Logic Pro X is a multi EQ. A multi EQ is basically a parametric EQ with other types of EQs added into it’s functionality, such as a high and low shelving EQ
  1. Parametric EQs have at least one sweepable frequency control that you can use to select any frequency in the EQ's frequency range; typically from 20Hz up to 20kHz, which happens to be the normal range of human hearing.

  2. Parametric EQs also have a control to select how much of the adjacent frequencies to the selected range are affected, commonly called The Q Factor—Q for short— or Resonance. If you adjust the Q, you can see the EQ curve widening or narrowing to affect more or less of the surrounding frequencies.

  3. Finally, parametric EQs typically have an analyzer option that lets you view the frequency curve of the incoming audio signal.

There are other features unique to Parametric EQs that make them very versatile, but it is these three features that let you perform the frequency sweeping technique.

How and Why It Works

Before performing this technique, it is a good idea to have an understanding of what you are doing so you can know what to look for. You can think of this technique as using an EQ like a magnifying glass for your audio, exaggerating and magnifying individual frequency bands almost on a harmonic level for you to be able to have a closer inspection audibly.

This technique is useful for locating problem frequencies that are in need of adjustment; typically by turning them down. Notch filtering is when you remove a very narrow band of frequencies. 

If you've ever heard anybody say something to the effect of, “There is a loud Bb in there,” referring to almost any type of sound when producing, this is a case when you would want to sweep the frequencies to locate and “notch out” said unwanted harmonic.

Sweeping the Frequency Spectrum

Sweeping the frequencies of an audio source is a deceptively simple technique, but once it's usefulness is realized in your day-to-day workflow, it will be a welcome but of production knowledge.

  1. First you want to insert a parametric EQ on the channel you want to analyze and enable the EQ’s analyzer function. This feature is not absolutely necessary, but it makes this technique more intuitive.

  2. Next, select one of the sweepable parameters of the EQ. It doesn't matter which band you use, as long as it can be set anywhere in the frequency range. If you are going to be using more than one band of a single EQ plug-in, it can be good to select the bands in succession for organizational purposes.

  3. Then you want to set the gain very high, and the Q so that there are no adjacent frequencies being affected. Finally, set the frequency selection to as high as it will go. This is the beginning point of the sweep.
Your EQ should resemble something like this, where the spike is the band that you are going to "sweep" across the frequencies.

Tip: Make sure your volume is at a safe level. This is a technical technique more so than a creative one. You want to be able to comfortably hear the audio without fatiguing you're ears.

Once you have the EQ set, start audio playback and begin to slowly move the frequency selection back and forth in a sweeping motion. What you want to listen for are any frequencies that when passed over are way too loud. Alternatively, if you hear a frequency that you want to remove or otherwise adjust, but are not sure which, listen for the problem frequency to become very noticeable when sweeping over. 

Once you have located the frequencies in need of adjusting, you can notch them out as much or as little as you deem necessary. The great thing about most parametric plug-ins is they have multiple sweepable parameters, so you can use a single instance to make multiple corrections.

Audio Examples

Piano Passage

This audio example is a bit extreme. It's from a piano passage of a song I produced. The keys are played in quick succession, which causes the harmonics to build up over time. 

You can noticeably hear the frequencies, but unless you have perfect pitch hearing, you may not know exactly where these frequencies are, making this a good candidate for sweeping to reduce some of the buildup. 

Piano before EQing:

Piano after EQing:

Drum Groove

This audio example is a drum groove that I programmed using two layered snare samples—one of an acoustic snare, and the other a digital noise type snare. The acoustic snare sample has a high C to C# overtone that is sticking out and distracting from the rest of the groove, so I want to remove it. 

Drum groove before EQing:

Drum groove after EQing:


Sweeping the frequencies of an audio source is a great way to make fine-tune adjustments to your sound. This attention to detail will give your final mixes that professional and polished sound that comes from a high attention to detail. I hope this technique comes in handy when working on your next project.
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