What’s going on down there?

Why is it so hard to get the low-end balance of your mix right? Two reasons are limitations of monitoring and limitations of human hearing.

Instead of hearing pitch on a linear scale, we hear it lograithmically. Put simply, this means that we hear in octaves of frequency, rather than Hertz by Hertz. The first octave we can hear is between 20Hz and 40Hz, whereas the next is between 40Hz and 80Hz, the next between 80Hz and 160Hz, and so on. The differently spaced vertical lines on a frequency analyser or EQ graph give a good representation of this.

In fact, the human auditory system works somewhat like a FFT frequency analyser, and

doubling

similarly, the frequency resolution in the lower octaves is poorer than those higher up. The relevance of this is that it makes it harder to discern pitch the lower it goes.

There are other ‘head tricks’ going on such as our pitch perception relative to volume: try listening to a bass part loud, then turn it down quickly to hear how the pitch can appear to change, for example. Another more important one is bass balance and volume. The louder the volume, the higher the relative level of the bottom end (and to an extent the top end). This is the reason for a ‘loudness’ button on hi-fis, to compensate for the perceived lack of bass frequencies at low volumes. This latter psychoacoustic phenomenon is vital to comprehend and master when balancing bass because it’s very easy to go over the top and make your mix too bassy if you’re monitoring quietly, or conversely too quiet if you’re mixing at volume. This is a key reason why it’s important to test your mix on multiple monitors and headphones, in different environments, comparing it to commercial reference tracks you are familiar with.

The limits of your monitors and listening room are a learned process. The more you work in a space and compare it to other spaces, the more you get to know how a mix should sound in order for it to translate.