Hello! Welcome back to your course on sound engineering.
In our last lesson, you learned how to perform sonic surgery, using a narrow bell filter and the "sweep and destroy" method to remove specific problematic frequencies. This is an essential skill for cleaning up recordings.
Today, we continue with subtractive EQ, but we're shifting our focus from narrow problems to broad cleanup. The goal for this lesson is to learn how to apply high-pass and low-pass filters to remove unnecessary low-end rumble and high-end hiss. Think of this as cleaning the windows of your mix; by removing the grime at the extreme low and high ends of the frequency spectrum, you allow the important musical information in the middle to be heard with much greater clarity.
1. The Sonic Brooms: High-Pass and Low-Pass Filters
While a bell filter is like a scalpel, high-pass filters (HPF) and low-pass filters (LPF) are more like brooms, sweeping away entire sections of the frequency spectrum.
- A High-Pass Filter (HPF) cuts frequencies below a set point, allowing the higher frequencies to "pass" through. It's your primary tool for eliminating low-end "rumble"—unwanted noise from air conditioners, microphone stand vibrations, or frequencies from an instrument that just don't belong in the bass region.
- A Low-Pass Filter (LPF) cuts frequencies above a set point, allowing the lower frequencies to "pass" through. It's used to tame "hiss" or excessive high-frequency "fizz" from synths, cymbals, or noisy recordings, making them sound warmer or pushing them further back in the mix.
To understand the basic function and purpose of these filters, the following reading provides a great overview.
The Ultimate Guide to Pass Filters in Music Production
The article 'The Ultimate Guide to Pass Filters in Music Production' clearly explains what these filters do and when you would want to use them for cleaning up your mix.
Read the sections 'The Basics of Pass Filters', 'High-Pass Filters (HPF)', and 'Low-Pass Filters (LPF)'. Focus on how they are described as tools for removing 'clutter' and 'harshness'.
2. Filters in FL Studio: Fruity Parametric EQ 2
In FL Studio, you will use the same tool as last lesson, Fruity Parametric EQ 2, to apply these filters. You simply change the type of an EQ band to either a "High pass" or "Low pass" filter.
There are two key parameters you'll control:
- Cutoff Frequency: This is the frequency where the filter starts working. You move the band left or right to set this.
- Order (Slope): This determines how aggressively the filter cuts the frequencies. A "Gentle" order rolls off frequencies slowly, while a "Steep" order creates a very sharp cut. You access this by right-clicking the band token.
The following video is an excellent guide to using filters specifically within Fruity Parametric EQ 2.
The Best Way To Use Fruity Parametric EQ 2 - FL Studio Basics
The video 'The Best Way To Use Fruity Parametric EQ 2' by In The Mix is perfect for you as an FL Studio user. It will show you exactly how to set up these filters and, more importantly, how to avoid a very common beginner mistake.
First, watch from 01:07 to 04:40. This part introduces the HPF and LPF filter types and the 'Order' setting in Parametric EQ 2. Then, pay close attention to the segment from 05:41 to 08:02. This section highlights the critical difference between using a proper High-Pass Filter versus simply turning down the default low-shelf band. Understanding this will save you from a lot of muddy mixes!
Test your understanding!
After watching the video, explain in your own words why using the "High pass" filter type is more effective for removing low-end rumble than just using the default "low shelf" on Band 1 and dragging it down.
Show answer
A low shelf only turns down the frequencies below its cutoff point by a fixed amount (e.g., -18 dB). This means some of the low-end rumble still gets through, just quieter. A high-pass filter, on the other hand, continuously attenuates frequencies more and more the further they are below the cutoff, effectively removing them entirely and providing a much cleaner result.
3. Practical Use: Cleaning with Filters
Now let's see these filters in action in a musical context. Your goal is to remove frequencies that aren't contributing positively to the sound, which in turn creates space for the instruments that do need those frequencies (like the kick and bass).
Removing Low-End Rumble with an HPF
Almost every track in your mix, except for your kick and sub-bass, is a candidate for a high-pass filter. Vocals, guitars, synths, pianos, and even cymbals often contain low-frequency energy that you can't really hear but which collectively builds up into "mud" and consumes valuable headroom.
Taming High-End Hiss with an LPF
Low-pass filters are used more selectively. They are great for taming overly bright or harsh sounds, like a piercing synth lead or fizzy cymbals. By rolling off the extreme high-end, you can make an element feel warmer and sit more naturally in the mix.
The next video demonstrates both of these techniques beautifully.
How To Become a Master at EQ (in Only 15 Minutes)
The video 'How To Become a Master at EQ' provides clear, practical examples of using both HPF and LPF in a mix. You'll see exactly how these moves help instruments fit together.
Watch the segment from 06:12 to 08:14, where the presenter applies a high-pass filter to a piano to stop it from clashing with the bass. This is a perfect example of removing low-end rumble. Then, watch from 13:02 to 14:19. Here, he uses a low-pass filter to tame a sharp lead synth, making it sit better in the track. This shows how to remove unwanted high-end harshness.
Best Practices: How Far to Go?
The most common question is: "Where should I set the cutoff frequency?" There is no single answer, as it depends entirely on the instrument and the mix. The process is about listening carefully.
- For a High-Pass Filter: Slowly raise the cutoff frequency while the track is playing in the context of the mix. Stop when you begin to hear the instrument's fundamental character get thin, then back it off slightly. You want to cut the mud, not the body of the instrument.
- For a Low-Pass Filter: Slowly lower the cutoff frequency. Stop when you begin to hear the sound become dull or lose its presence, then raise it back up a bit. You want to remove the fizz, not the sparkle.
Caution: A very common mistake is over-filtering. Being too aggressive with your HPF can make your entire mix sound thin and weak. Be especially careful with instruments that have important low-mid information, like vocals and acoustic guitars. Always A/B your EQ (toggle it on and off) to confirm that your change is actually an improvement.
Conclusion
You have now added two of the most-used tools in mixing to your arsenal. Applying high-pass and low-pass filters is a fundamental step in almost every professional mix to achieve clarity and separation.
Key Takeaways:
- High-Pass Filters (HPF) cut low-frequency rumble and are used on most non-bass instruments to clean up mud.
- Low-Pass Filters (LPF) tame high-frequency hiss or harshness and are used more selectively to warm up sounds.
- In FL Studio's Parametric EQ 2, you must select the correct filter Type and adjust the Order (slope) for the desired effect.
- The key to setting the cutoff frequency is to listen in the context of the mix and cut only what is unnecessary, avoiding making the track sound thin or dull.
In the previous lesson, you tackled specific problem resonances with bell filters. Today, you've learned to clean up the extreme ends of the spectrum. In our next lesson, we will combine these ideas to tackle one of the biggest challenges in mixing: using EQ to create frequency separation between two competing elements in a mix, like a kick drum and a bassline.