Keeping It Real: Psychoacoustics In IEM Mixing

This ability to hear frequencies distinctly is known as frequency resolution, which is a type of filtering which takes place in the basilar membrane of the cochlea. When two sounds are very close in frequency, we can’t distinguish between them and they’re heard as a single signal.

Someone with hearing loss due to cochlea damage will typically struggle to differentiate between consonants in speech.

Why It Matters

This is an important phenomenon to be aware of when mixing. The frequency range to which our hearing is most attuned, 500 Hz to 5 kHz, is where many of our musical inputs such as guitars, keyboards, strings, brass and vocals reside.

When we over-populate this prime audio real estate, things can start to get messy. This is where judicious use of equalization becomes very useful in cleaning up a mix – for example, although a kick drum mic will pick up frequencies in the mid-range region, that’s not where the information for that instrument is.

The “boom” and “thwack” that characterize a good kick sound are lower and higher than that envelope, so by creating a deep EQ scoop in the mid region, we can clear out some much needed real estate and un-muddy the mix.

Incidentally, because of the non-linear frequency response of our hearing, this also tricks the brain into thinking the sound is louder and more powerful than it is. The reverse is also true; rolling off the highs and lows of a signal creates a sense of front to back depth and distance.

It’s also worth considering whether all external track inputs are necessary in a monitor mix – frequently pads and effects occupy this territory, and while they may add to the overall picture on a large PA, are they helping or hindering when it comes to creating a musical yet informative IEM mix?

Next time we’ll examine the acoustic reflex threshold, the Haas effect, and how our brains and ears work together to determine where a sound is coming from; and we’ll also explore what it all means for IEM mixes.