It is usually better if there is some separation between the guitar and the bass. If they occupy some of the same space in the frequency range, one or both will be hard to hear, and the song may become a lot less interesting.
A high pass filters for the guitar
An easy way to separate the guitar and the bass is to simply remove low, bass-like frequencies from the guitar track. To do so, we use a high pass filter.
Here is a guitar track from a song we recently worked with. This track contains three different sections of the song, some of which are busier than others. That is so we can compare different sections before and after the high pass filter. There is a lot of distortion, yes. That is important, as we will see below.
The following clip is the same guitar piece, but after a high pass filter. The difference is very noticeable, even with the mp3 compression for this post.
In my opinion, the first clip – the one before the high pass filter – sounds better. It is more melodic. The second one is thin and that makes it a bit boring. But, of course, these are taken out context. They are very different when placed in the song.
Where is the high pass cutoff? In other words, what is the frequency, above the high pass filter will pass frequencies unchanged and below which the high pass filter will stop frequencies? That depends on the song. In this case…
The high pass filter on the guitar is a compromise (in this case)
The second clip above is, in fact, a compromise. There is a lot going on in this song, as you might have guessed just from the guitar piece. My first inclination was to cut high – over 200 Hz.
This worked. The guitar and bass were nicely separate and both very audible. However, the guitar lost its melodic undertones. Much distortion was left. Most importantly, the song lost a lot of energy. There was some interesting, perhaps confusing interplay between the guitar and the bass that made you pay attention and that was now gone.
My second attempt was to cut slightly lower – somewhere between 150 Hz and 200 Hz. There was still overlap between the bass and the guitar. They were not as nicely separate. The song now sounds less produced, a bit more confusing, and slightly sloppy. But it kept its energy.
Energy is what I want. Perhaps I want it now. I may wake up tomorrow in a different mood and decide otherwise. For now, I am sticking with the second clip above – my compromise between production and energy.
The guitar and bass do not always need separation
A couple of words of caution. Some of the things discussed below are difficult to hear in the corresponding clips with my cheap headphones. And it is all compressed to mp3. But it is worth a try.
Here is a sample of a song, in which the guitar and bass play the exact same thing (vocals excluded). The bass and guitar a hard to untangle, but this sounds good to me (except for some hum in the guitar). I would not touch it.
Reference points for the guitar and bass
Listening to the same song over and over makes mixing difficult. The brain gets used to and expects a certain sound. Problems become difficult to hear.
We have two approaches to addressing this. First, we often leave songs for a week or so. Second, we have a reference song – another song in which the guitar or bass sound the way we want them to sound.
Here is my reference point for the bass (vocals and solos excluded).
Fixing the bass
Back to the song with the guitar and its high pass filter. It all started with the bass. There was an interesting bass line, but a less than interesting bass recording. The bass had treble and rumble, but not much of a body.
Time permitting, the bass should be re-recorded. Time not permitting, the rumble should be reduced. My approximate equalization to remove rumble was the following notch, with some additional high shelf gain, which, at a minimum, made the initial accent of notes more pronounced. It also gave the bass a bit of a distorted quality, but I don't mind that.
Deconflicting the guitar and bass
Just for fun, here is a clip of the result – after the bass equalization and the guitar high pass filter. It is busy, yes, аnd that is not even all the tracks in that section. Тhat is what makes it fun.
And, yes, this song has some additional problems. I remember that we recorded the drums on a set with a broken crash and a loose snare. The kick could be better. It is too popping. The bass is a bit in and out. Some instruments come in too early or late. Maybe we will fix all of this.
Or not. I like this song energetic and loose. At the end of the day, it is all about subjective taste.