In the world of audio engineering, Equalization (EQ) is one of the most fundamental tools used to shape and refine audio. Among the various EQ techniques, high pass and low pass filters are essential for achieving clarity and balance in a mix. In this brief guide, we’ll explore what these filters are and how they can be effectively used in the mix and in audio engineering as a whole. Read this article all the way through and I’ll toss some practical applications your way as well! Or skip to the bottom if your want. Live your life.
High Pass Filters
A high pass filter (HPF) allows frequencies above a certain cutoff point to pass through while attenuating frequencies below that point. This is particularly useful for removing unwanted low-frequency noise and rumbles in a given recording. Believe it or not but there are cluttery low end frequencies everywhere. Using a high pass on cymbals is a great way to ensure you get that crispy “kshhh-kshhh” crash or china we all know and love!
Applications:
- Vocals: Applying a high pass filter to vocal tracks can eliminate low-end rumble and background noise, making the vocals sound cleaner. Typically, setting the HPF around 80-120 Hz works well, but this can vary depending on the vocalist and the recording environment.
- Guitars: Electric and acoustic guitars benefit from HPFs to remove unnecessary low frequencies that can muddy the mix. Setting the cutoff around 100-150 Hz helps to achieve a more focused sound.
- Drums: For overhead and room mics, a high pass filter can reduce low-frequency bleed from other instruments and room noise, providing a clearer capture of the cymbals and overall drum kit.
Low Pass Filters
A low pass filter (LPF) does the opposite of an HPF; it allows frequencies below a certain cutoff point to pass through while reducing the higher frequencies. This is useful for managing and shaping the high-end content of a track as well as the low end of say a kick drum or a bass guitar. Using an LPF can help to focus the sound and feel of lower voiced instruments
Applications:
- Bass Instruments: Applying a low pass filter to bass guitars or synths can remove unwanted high-frequency noise, making the bass sound more solid and focused. A common setting might be around 5-8 kHz, but it depends on the instrument and the mix.
- Background Elements: Low pass filters can be used on background elements like ambient pads or effects to keep them from interfering with the clarity of the main instruments and vocals. Setting the LPF around 8-12 kHz can help keep these elements subdued.
- Percussion: For percussion elements that don’t require high-frequency content, such as congas or bongos, a low pass filter can help them sit better in the mix without clashing with other instruments.
Practical Tips
- Subtle Adjustments: When using high pass and low pass filters, subtle adjustments are often more effective. Avoid setting the cutoff frequency too high or too low, as this can overly thin out or darken the sound.
- Use in Context: Always apply filters in the context of the entire mix. Soloing an instrument while applying EQ can be helpful, but it’s crucial to hear how it interacts with the other elements in the mix.
- SUBTRACTIVE BEFORE ADDITIVE EQ: Really this could be its own post but always always ALWAYS apply subtractive EQ before additive eq. In laymans terms – always remove troublesome frequencies from a signal before you add to that same signal. This helps to ensure you arent making those troublesome frequencies an even bigger issue. For all you visual learners out there the below screenshots should help.
Subtractive eq
Additive EQ
With that in mind, when using a high or low pas filter, that should always be done before enhancing any of the other frequencies since both of them are inherently subtractive filters. In conclusion, high pass and low pass filters are invaluable tools in an audio engineer’s arsenal. By understanding and applying these filters appropriately, you can achieve a cleaner, more professional sound in your recordings. Experiment with different settings, and always trust your ears to guide you to the perfect mix.