HPF is your Friend

How do you get tight, full, clear bottom end in your mix? This is one of the most challenging aspects of most mixes. One reason it is challenging is that the answer is unintuitive. Cut the low end.

Every instrument in your mix has a useable range of bottom end. Everything below a certain frequency contributes to mush and mud. If your bass instruments are competing with (or contributing to) this mush, your mix may sound flabby and undefined. For example, your kick may not cut through and just sounds like cardboard rather than a kick drum.

Even your bass instruments (kick, bass, possibly synths or effects) need to be carefully managed to not have unnecessary bottom end. In most mixes, either the kick or the bass own the low end. Imagine how you want the song to sound in your head and try to figure out which is really holding the bottom. Listening to reference songs in similar styles can help you make this decision.

If the kick will be your bottom, you may boost it around 60-80hz by 2-3db. Use a High-Pass Filter (HPF) to roll off everything below 40hz (yes, even on your lowest frequency element). Take a scoop out of the kick between 150-250hz. The amount of cut depends greatly on the kick source. If you recorded a real kick you may need to take 8-10db or more out with a fairly wide Q. This will tighten the sound, give it more punch and (counter intuitively) make it feel as if it has more bass. Sampled kicks probably already have similar EQ applied so you won't need to be as drastic. Now for the Bass, you want to use the HPF to roll off gently below 80hz. Take advantage of the hole you created in the kick by boosting the bass in the 150hz range slightly. You can take a wide-Q cut in the midrange (300-500hz) of 2-3db.

If bass is your primary bottom end, you do the opposite. Another trick to extend the bass is to use a subsonic bass plug-in or add a MIDI track with a sine wave synth sound down 1 octave from the real bass. Now the real bass can be EQed to maximize clarity and punch and the synth handles the extreme lows. You guessed it - use an HPF to cut everything below 100hz or so.

Now lets apply that HPF on your non-bass instruments. This is sometimes hard to do when you listen to the instruments alone. You worked hard to get that beefy guitar tone and now you are butchering it. Remember you are working to create a piece of music that will have an emotional impact. You need to serve the entire mix.

If the bass and guitar are mostly playing in unison, you can filter out below 200hz on the guitar, sometimes higher. Acoustic guitar in a busy mix can be filtered below 350hz. Lead vocals around 100hz and backing vocals around 200hz. Snare & toms around 150-200hz. Cymbals and other percussion up to 500hz or higher. Piano, synths and other instruments can vary greatly depending on the purpose of the part. Think about that purpose and how much bottom end you can do without. All of these cuts can help smooth the dynamics and help the instruments blend in the mix with less compression. (The peaks that stick out often have lots of lower end content). And now your low end is clear to shine through without blasting it.

It is important that there are low frequencies in your bass instruments. Most likely it is there.. you don't need to boost it. You need to carve away the mud to expose it - like carving a face out of a piece of wood.