High-Pass Filter Tips - Individual Tracks and Mastering

[Ted]

The discussion of one of my songs has turned into a deep discussion on using High-Pass Filters (HPF). As much as I like having my song bumped again and again, I think it might be good to create a specific topic.

I'm not an expert on this, but I will do my best to summarize what the deal is.

A high-pass filter (HPF) is an audio effect that allows high frequencies to pass through while reducing or eliminating low frequencies below a certain cutoff point. It's used to clean up individual tracks or during the mastering process.

Individual Tracks

When applied to individual tracks, a high-pass filter can help remove unnecessary low-end rumble or muddiness that may not be essential to the sound of a particular instrument. For example, filtering out the deep bass frequencies from a vocal track can prevent them from interfering with the low end of the bass guitar or kick drum, making the mix cleaner and more defined.

Mastering

In mastering, the HPF serves a slightly different purpose. Here, it's typically used to ensure that the final stereo mix is free of excessive low-end energy that could cause issues on different playback systems, like speakers or headphones with poor low-end response. It also helps prevent distortion or problems with volume levels that may occur when too much low-frequency content is present in the final track.

Infrasonics (frequencies so low humans can't hear them)

Infrasonic frequencies can still take up valuable space in the mix and waste headroom. Even though we can't hear them, they can still affect the overall energy of the track or cause issues in the mastering process, such as distortion. By removing these unnecessary frequencies, you can improve clarity, enhance focus, and make sure the track translates well across various playback systems.

Videos

https://www.youtube.com/watch?v=tK4niEYUo-Q


https://www.youtube.com/watch?v=4V2dh0gz4xg


https://www.youtube.com/watch?v=DvJ5O5n4ksE

Sage Advice from Songcrafters

On the filtering, I also take everything out below 50Hz or so. I even do it during tracking and mixing - I don't want the bottom end clogged up with stuff I can't even hear!

I believe the wisdom is, for the kinds of music I dabble in, it's wasted energy/headroom. I believe this still applies nowadays, even if you're not mastering for vinyl.

[Because I use a Micro BR] I don't do per-track HPF tweaking. I just do the HPF on the overall mix [the master, after exporting from the MBR to a WAV]. These are my settings.

30Hz is just below the B string on a 5-string bass (B0) – and that's about where humans start to lose the ability to hear low notes

I do it to pretty much everything on a track by track basis, although less aggressively on kick and bass.  On things like vocals, strings and woodwinds I often go much higher just to clear as much space as possible - unless your vocalist is Paul Robeson it really isn't going to be noticeable if you take out everything below 100hz.

I pretty much do high pass filtering track by track too - and pay some attention to the mix at mastering stage just in case the mix (via the plugins) has introduced a bunch of bottom end I didn't notice. Now that my reverb busses have huge low cuts on, it doesn't happen quite so often.

[TPB]

Very nice explanation
Tim

[Farrell Jackson]

This is some food for thought on high pass filters. Thanks for putting these videos up Ted.

[Ted]

I particularly appreciated the "rule of thumb" from the first video.

A good rule of thumb for any pitched instrument is to identify the lowest note played or sung, find its frequency on a chart, then set a high-pass filter an octave below that frequency. Use a filter with at least a 24 dB per octave slope to remove unnecessary sub-frequencies while preserving the fundamental tone, ensuring a cleaner mix.

And for a frequency chart, I'm oriented to bass and guitar. I can never remember whether "open E" is E0, E1, or whatever. So here's a useful chart (poached from TalkBass.com)

And for "an octave below" the lowest note played or sung, find the frequency of that note and divide by 2.

Example: If the lowest note is B – Guitar, second fret on the A string – that's approximately 123 Hz. So an octave below is 123 ÷ 2 = 61.5 Hz.

[Zoltan]

And for a frequency chart

You should have saved this chart for the Halloween!

Just kidding... Carry on

[StephenM]

that chart is handy Ted... thanks...