What Is a Filter Sweep and How Can I Use It

closeup of Moog synth filter dials

+ Producers, Synth Heads and Sci-Fi Nerds, our new course with synthwave pioneer, Com Truise: Mid-Fi Synthwave Slow-Motion Funk, is out now!

Today’s digital mixing platforms are incredibly powerful, versatile, and provide countless different effects options to add character and flavor to your mixes.  Knowing how and when to use different effects can help you best apply them to your mix, the way an expert painter knows which colors to choose and how to blend them to achieve the best visual representation of their goal. 

One of the most enduring effects that’s been part of many well-known sound producers’ arsenals for over half a century is the filter sweep. 

And even though it’s been around for so long, it’s still a highly useful and capable effect that just might add the right spice to give your music that perfectly seasoned sound. Let’s dive in!

But first, speaking of production tools, we wanted to share a handy explainer from our YouTube channel on how the oscillators and waveforms work in your synth, and how this knowledge can help you design custom patches for any imaginable sound!

What exactly is a filter sweep?

A filter sweep is accomplished through the use of high pass or low pass filter or narrow band parametric EQ which has the frequency it’s being applied at sweep across a range of tones as the music progresses. Hence, the name “filter sweep.” 

It can be done quickly and in time with the beat to provide a musical swooshing type of effect

Or, it can be done slowly over a period of time to gradually uncover the full sound of a musical piece, either starting with only bass sounds and slowly adding in midrange and then treble tones, or starting with only treble sounds and slowly adding in midrange and then bass tones.

+ Read more on Flypaper: “How to Create the Unmistakable Keyboard Sound in ‘Everything in Its Right Place’.”

Where has it been used?

The filter sweep effect has been in use for decades in many different genres of sound.  Hiphop beats have used it many different ways for years and it’s been a common DJ intro trick for just as long.  If you want to hear how it’s been used to alter synth sounds, a couple well known examples are “Tom Sawyer” by Rush.

And the Stranger Things theme song.

When should I use it?

If you’ve been looking to add some interesting character to an otherwise standard instrument sound you might want to consider applying a one time or repeating filter sweep to that sound. It can introduce a dynamic feeling to an otherwise static, unchanging presence by that instrument within the mix. 

Other common places where filter sweeps are used is as transitions, intros, and outros in a song, where you’re looking to present a slightly different variation on the sound that’s heard elsewhere in the song as a way to ease in or out of the song or shift between movements within the song. 

And, because it can be so recognizable when applied in certain ways — such as in many ’90s and ’00s DJ-style beat intros and ’80s style synth effects — it’s a fabulous go-to sound if you’re looking to recreate something reminiscent of those genres and eras.

How do I apply it and fine tune it?

There are many ways to apply a filter sweep, but one of the simplest is to use an EQ effect insert in your mix set to boost or cut the sound, and then automate the frequency at which it’s applied to fully sweep over a wide range of tones during a specific desired period of time. 

For example, you could apply a narrow band EQ boost of +6dB starting at a frequency of 200Hz, which then sweeps up to 2kHz over four beat counts. This would produce a rising filter sound that takes four beats to fully rise from a low pitch to a high pitch adjustment to the original sound it’s applied to.

Another example is shown in the images below, using Logic Pro X. In this instance, the low cut filter on the native EQ effect insert in Logic has been set at around 8kHz, effectively cutting off all but only the highest treble sounds.  The result is a wispy, tinny sound to start. 

Then, over the full length of this particular audio clip, automation is used to drop that frequency all the way down to 20Hz, effectively adding in the full audible version of the clip by the end. 

This would be reminiscent of a DJ beat intro which starts with a tinny treble sound, slowly adds in some midrange tones, and eventually fills in with the bass beat by the end of the sweep.  

[Automated low cut frequency in Logic Pro, reducing from 8kHz to 20Hz over length of audio clip]

[At the start of the audio clip, the low cut filter will be applied as shown here, beginning at 8kHz]

[By the end of the audio clip, the low cut filter will drop to 20Hz, and effectively have no filter remaining]

There are numerous other ways you can experiment with applying this type of EQ automation. Give it a try the next time you are looking for an interesting transition or character change to an instrument sound. You’ll be amazed at how much impact such a simple sonic device can have in your mixes and production work.

It’s no small wonder that the filter sweep has been used for so many years, and continues to be a regular go-to device for producers and engineers to this day.

Don’t stop here!

Continue learning with hundreds of lessons on songwriting, mixing, recording and production, composing, beat making, and more on Soundfly, with artist-led courses by KimbraCom TruiseJlinKiefer, and the new Ryan Lott: Designing Sample-Based Instruments.

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