What is a low pass filter?

When you start working with an equalizer you will often hear people mentioning low pass filters. At first, it would seem like a low pass is just another function in the equalizer.

This completely changes when you start to work on songs and all their elements, as you sometimes find that this is the only function you would use in a song.

As a novice music producer, using the low pass filter might at first seem like an easy task. A low pass filter is after all the first thing that you have to properly master in an equalizer.

Even though there is so much to explore, understanding a low pass filter will ensure that you can clean up the high end and progress from there.

When you start mixing it might get confusing at first, because of the sheer amount of information that is thrown at you. If you understand what concepts are being performed in the mixing stages, everything will make sense and fall in place.

A low pass filter is used to sweep from right to left. It helps clean up the high end of a frequency spectrum. The low pass can be used to clean up the high end that is not required for the track. This makes sure that the track is safe from harsh high-end sounds that are not added to the track.

Just knowing that a low pass filter is important for music production and equalization is one thing, but understanding how they work and how they are used to make a song shine will help anyone wanting to learn equalization tremendously.

In this article, I will go through the low pass filter and how to use it. Let’s get started, shall we?

What is a low pass filter? 

A low pass filter can also be called a high cut filter. It cuts the high end and moves from right to left. The low pass filter can be used for instruments that have too much white noise in the top end of the frequency spectrum.

When using a low pass always make sure that the total gain dB is lower than 6 to make minor adjustments or else you will end up boosting the master volume, which might result in clipping.

Low pass filters will come in handy when you are working on a rhythm for a song. You will have so many bass-heavy elements to mix and often the first solution you turn to is a low pass filter.

This will clean up most of the problems that are in the elements that have been added to the song. Usually, the high end of a drum element will have reverb and vibration of the components of the instrument or the recording environment.

This is not desirable when drums are going to be used in a commercial song. The best way to add a low pass filter over a lot of elements is by adding them to each bus strip of a mixing board. This will make sure that the track is being cleaned properly.

Where can you use a low pass filter? 

Low pass filters can be used in almost all instruments and vocals, based on their needs in the track. Let’s look at each element in a track to analyze how it should be used.

When it comes to vocals, you probably don’t need the low pass filter for a female vocal. This is because most of the details and information in a female vocal lies in the high treble section of the song.

Since low pass cuts the high and allows the low end to come through, if applied, it would take away crucial detail from the high end. That said, a high pass filter is usually applied for vocals.

When it comes to piano and instruments, a low pass is used when there is more information in the low end. Whenever the music producer wants the low end to be intact, and the information in the high end to be cut, low pas is used.              

When it comes to drums, the lower end is a crucial part of the frequency spectrum. It is always preserved and the higher end is cut off. This might not be the case in certain drum elements such as the high hats, where the entire information lies in the high end of the frequency spectrum.

When it comes to bass, there is always a cut at 19 kHz to stop squeaky sounds from the bass guitar, and only allow the good tones to shine through. This hard cut at 19 kHz is usually done by a low pass filter which tapers off in the edges. 

When it comes to strings, a low pass is not used, but instead, a high pass is used to clean up the low end.

How to use a low pass filter? 

Using a low pass filter starts by setting the Q value in the equalizer, this is nothing but the gain level at the edges of the tapering point. The tapering point is where the frequency cut-off beings in a low pass filter.

When you have set the Q value in the equalizer, it’s time to start looking at the element that is subjected to the low pass filter.

Based on the element, it will select which frequency you want to cut off from the particular spectrum. Once you have made up your mind on what you want to remove, sweep the curve, and take it from right to left until you reach the desired frequency.

One important thing to make sure of while doing a low pass filter is the ability to cut hard or even have a slope in the curve of the filter. This can be made possible with the help of the Q value set at the start of the low pass filter application process.

 You can always go back and reverse what the track requires in the frequency spectrum. Be minimal in working with the filter curves as they tend to boost a lot in the master track when not optimized properly.

When you are done with the low pass filter, invest time in learning about the high pass, as the only difference between them is the operating frequency range of each filter in the spectrum.

How do I know if I have a high pass or low pass?

If the filter moves from left to right it’s a high pass filter. It allows the higher frequencies to pass through. If the filter moves from right to left it’s a low pass filter. It allows the lower frequencies to pass through.

What is a low pass filter used for?

A low pass filter is used for cleaning up high-end harsh sounds in instruments and vocals. This eliminates undesirable sounds in the high-frequency spectrum of a song or audio track.

How does a low pass filter effect music?

When you move a low pass filter from right to left, it will slowly take away the treble from the song. You will be left with just the bass in the low end. This is used to eliminate the harsh sounds in drums and bass at the top of the mix.

How do you calculate the gain of a low pass filter?

The gain value of a low pass filter can be calculated with the help of the q value in the equalizer. The value, of the q value, will determine how much gain is applied over a particular frequency band. Nowadays all equalizers will mention the gain value as the calculations are too complex to do individually.

The bottom line

A low pass filter can save a music producer from a lot of hassles if used properly in a mixing session. Learning how to first use a low pass filter will give you an idea of how the filters in an equalizer work with each other.

Equalization is really broad; don’t get frustrated if you do not understand how to do something. Instead, put your time into learning other concepts and come back to this.

Click this link to find out more about equalization.

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