Audio Recording

This is a short guide on how to effectively use low pass filter and high pass filter in your home mixing and mastering sessions.

Let’s start with the properties of a filter. You might have read our post on What does a High Pass Filter do? – Technical Explanation and Plot , so you have a clear idea of how the high pass filter works.

A filter is a signal processing unit that “attenuates” specific range of frequencies. Based on that definition, you might consider a parametric or a graphic equalizer as a “filter” also; yes it is.

But what makes a low pass filter and high pass filter special is the ‘shelving” action on a wide limit of frequency ranges or even to infinity.

By definition>

A “low pass filter” allows frequency lower than the cutoff frequency to pass while severely attenuating above it.

So for example, if the cutoff frequency of the low pass filter is 16Khz, then it is said to pass or allow 16Khz below while attenuate severely the frequencies above 16Khz.

This is opposite to high pass filter which allows high frequencies and block lower than the cutoff.

So how are you going to use these tools in a mixing and mastering session?

1.) Low pass filter is used to remove high frequency related “hiss” and cleaning of upper frequency spectrum, such as applying a cutoff at 16500 Hz.(effective audio range is 20Hz to 16500Hz, the rest can be filtered.)

There are different kinds of low pass filter, I personally use Butterworth filter in Adobe Audition order 66.

Most commercial master recordings apply a low pass filter at around 16500Hz (this is done in the EQ stage of the mastering process). However, it is not popular to use a low pass filter in mixing process.

2.) High pass filter – I commonly use this filter during mixing but not so much in the mastering process. HPF is applied to vocals, guitars and other string instruments to avoid mud with the bass guitar or bass frequencies.

Example is the high pass filter applied to vocal tracks (cutoff frequency 200Hz).

One important distinction of high pass and low pass filters with the rest of the filters (like parametric equalizers) is the absence of Q in the settings. So if you are going to use high pass/low pass filters, you need to set one important value and that is just be the “cut off frequency”. Although in some scientific filters you need to set the “order”, which is the measure of steepness of the frequency attenuation (see screenshot above).