High pass filters in mixing

It’s commonly suggested that it is “correct” to apply a high pass filter to every track except the kick drum and bass. Doing this does two things:

  1. It keeps the low frequencies in the mix for the kick and bass, so that they sound as pure and focussed as possible. This helps in making the low frequencies as loud and clear.
  2. It reduces unwanted noise from the other tracks, which makes them more focussed. This helps in making the overall mix sound clearer and cleaner, and reduces the headroom required by this unwanted noise.

Like all mix techniques, however, there is a degree of balance and creativity required. Too little filtering may make your mix muddy and messy. Too much, though, will make your mix thin, light and empty. As producer and mix engineer, you must make a judgement as to the appropriate amount. Your approach will vary from track to track, and even from mix to mix. You will know the appropriate amount through experience and critical listening.

There are even some situations where the best approach is to avoid high pass filtering altogether. You might want to mix like this when you have a song that needs to be sparse and natural – usually with recordings of acoustic instruments and voices. I took this approach with my mix of A Day Too Long.

For other, more modern mixes, I approach each track individually. I gradually raise the high pass frequency until I hear it take away too much body. It’s often worth trying different filter slopes if they’re available. Often I’ll find that a straight high pass filter is too harsh (read: steep/extreme) so I’ll use it in combination with a low shelf EQ. I might set the high pass filter quite low – usually below 200Hz – and use the low shelf to reduce the body (lower mids) without drastically changing the character of the sound.

Even though I don’t use frequency analysers, others find them useful. Yellowfever, for example, suggests using a frequency analyser to visually find the frequency where a high pass filter wouldn’t affect the tone of the sound. 

-Kim.

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