High and Low Pass Filters on Vocals

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EQ settings for vocals sometimes feels like you’re trying to find buried treasure. An endless task of moving knobs and listening to the changes just seems overwhelming. Then comes the conversation about filters on vocals that almost always arises in every session.

There are a few things you can do to improve your vocal recordings and get them to sit in a mix. The first is using filters on your EQ to tighten up the high and low end spectrum. Filters on most EQ plugins have 3 main settings.

1. On/Off

2. Frequency

3. Curve/Slope

The first is obvious, so moving on to the second. Frequency is the point where the filter starts to engage. This is the point in the EQ spectrum where the audio is starting to be lowered or attenuated. On a High-Pass Filter (HPF) you are allowing the high frequencies to pass as you filter out the low frequencies. On a Low-Pass Filter (LPF) you are allowing the low frequencies to pass as you filter out the high frequencies. When these are used properly, you can clean up a recording to focus on the audio spectrum that you do want in the mix.

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For example, when you set your HPF to 50Hz it is only starting to attenuate the frequencies at that point. How much attenuation is based on the third parameter, the curve or slope. This is measured in dB octaves that are listed as 6dB, 12dB, 18dB, 24dB, and 30dB. These are referred to as ordered harmonics and a 6dB curve is a 1st order harmonic. This means that the signal level drops 6dB per octave. A second order harmonic is a 12dB slope and the signal drops 12dB per octave. The higher the slope the more severe the drop in audio signal becomes and approaches a “brick-wall” response, which is not usually favorable to your audio signal.

For vocals I like to use a 12dB slope for both the HPF and the LPF. Sometimes I’ll use a different setting if the mix needs some tweaking. For the HPF I typically start around 80Hz and then adjust the frequency based on the tone of the vocalist and the style of the music. It does take some time to train your ears to recognize the sound that you want for a mix. I don’t recommend making these changes with the track in solo mode. It’s better to have your track in the mix and listen to how the EQ adjustments affect your track and mix. Using a HPF correctly can help cut down on the rumble in a vocal track and tame some of the plosives that may happen if your vocalist is too close to the mic.

The LPF on vocals can be a bit more difficult to dial in. In many cases, the vocal spectrum in the high frequencies is OK to leave in the mix. If you’re trying to cut down on sibilance, it’s best to use a de-esser. However, if you want to shape the vocal to reduce the amount of high frequencies it has in the mix then you can use a LPF to get the job done. I’ll usually start around 10kHz with a 12dB slope and then sweep the filter frequency up and down to find a spot that works for the mix. Rolling off these high frequencies can make more room in a mix for other instruments or backing vocal tracks. Depending on the arrangement of the music you can get a tighter sound by filtering out these higher vocal frequencies.

For more info and visual tutorials, check out my audio mixing master class.

Taming the bass

Bass is the big monster in your mix that fills up a whole lot of your dBFS meter on the master buss. Bass can be a troublesome foe in your mixing quest, but do not fret! Bass has one big weakness, High-Pass Filters.  

High-Pass filters are mysterious to some mixing engineers, but not to us. High Pass filters can do wonders for a dense mix that has lots of different tracks. When your mix is too boomy or muddy, first try using some high pass filters on the tracks that don't necessarily need to have low bass frequencies. Rolling off the low end on vocal tracks will really help separate the vocals from the rest of the mix. This may also immediately shape up the low end of the entire mix. Go through each track and use your ears to attenuate the HP filter on each track for a more controlled bottom end to your mix. You may not even have to touch the bass track or the kick track.

Alternately, you should use Low Pass Filters on tracks that reside in the low end of the mix. Rolling off the high frequencies on the bass and kick tracks may open up more brilliance and space in your mix.  It's not too complicated, but it does take a little bit of practice to get used to using filters to control the low end of a mix. Be sure that you adjust the filters with the tracks playing in the mix. If you solo the track while you adjust the filters, you may not get the tone or control that you need when the tracks are put back into the mix. Soloing has it's place, but when you're trying to get tracks to fit together in a mix, it's best to adjust them while they're in the mix.