What Is a High-Pass Filter and What Is It Used For?

Many beginning and novice sound engineers see this little button on their mixing console and never really figure out what it does. This button is usually located just above or below the gain knob on an analog console and may be found in the EQ section of most digital consoles. So what button am I talking about and why should you care?

This is the High-Pass Filter and it is one of the console's most underused buttons.

What is a high-pass filter?

A high-pass filter is an audio frequency filter that cuts out frequencies that fall below a specific frequency level. These filters may be marked as /80 or /100 which simply mean that the filter will cut out those frequencies below 80Hz or 100Hz.

High-pass filters don't just simply hack off the frequencies, though. Like EQ's and crossovers, they have a slope associated with them that gradually attenuates (cuts) the frequencies below the selected level.

Do you really need to use the high-pass filter when you are mixing?

Yes. Every engineer, whether they are new to the job or an industry veteran, should be familiar with this filter and how it can help them in their mixes.

Think about your live mixes... there are numerous low frequency sounds that can arise on stage at almost any time during a gig. Maybe the vocalist bounces the mic stand around, with the mic still attached. The kick drum has too much low, low end and it is very muddy or maybe the backup vocalist, aka the bassist, has a very low voice and you need to make his voice easier to understand.

The high-pass filter can help you cut out those real low, muddy and sometimes annoying frequencies in almost any instrument or voice. The great thing is that if you're not sure what it will sound like, you can turn it on and off and hear the difference, without causing major issues to your mix.

How should you use the high-pass filter?

There are some simple guidelines for using the filter. The biggest is that it doesn't always need to be on, but can become a saving grace in certain situations. Here are a few guidelines to help you along:

    If the instrument or mic sound source doesn't use or reproduce the frequencies that the high-pass filter would cut out, then turn on the filter on that channel.
    Once you have set your basic mix for the show, engage the filter one-by-one on each channel and listen to the difference. If the sound is better with it on, leave it on.
    Finally... simply experiment. You may find that when you engage the filter on certain instruments or voices, it helps to give them a great sound that may fit a specific song or quite possibly the entire gig.

The high-pass filter can become your favorite button on your mixing console. Learn to use it and love it and it will help you create better mixes.

My name is Gerad Clarkson and I have been working in and around Pro Audio for over a decade. I started my own Pro Audio company, Audio Avenue, in 2011. I work with church tech teams, mobile DJ's and local clubs, to help them find the best gear that fits their needs and their budget.

Article Source: Gerad K Clarkson

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