In Part 10 of this series, we discussed how much to boost or cut. Now we’ll talk about where we cut and musically relevant reasons why.
Let’s start with the extreme highs and work our way down the frequency spectrum. Generally, we boost high frequencies to add clarity, presence (often referred to as bringing a sound forward in the mix), and adding a little thing called “air.” This is a technique that many mixers use to bring sheen or sparkle to a mix. It’s mainly applied to vocals, but other instruments can benefit from this technique as well. Adding “air” is nothing more than boosting EQ in the extreme high register, or at around 12-16kHz (centering at 14,000 Hertz). On the plus side, the result is a little more clarity, detail, and sparkle. It also serves to bring vocals a little “forward” in the mix in the recording. The downside is that boosting this range also brings out any noise and hiss.
It’s important to remember that this technique was born out of analog recording, where high frequency content was lost in numerous passes of tape, and more so when bouncing. As such, it was often left for the mastering phase.
In digital recordings, adding “air” can sound downright obnoxious, particularly if you’ve recorded at 48kHz resolution. The reason for this is due to high frequency “cramping,” which occurs when EQ curves approach the area close to half the sampling frequency (Nyquist frequency). The curve becomes increasingly steeper as you approach the upper end of the frequency range. The effects of HF cramping are exactly the opposite of what we want; a reduction of high frequency response, causing the sound to be less open, and with added harshness. If you record at 88.2 or 96kHz, the problem is greatly reduced. Use an EQ plug-in that has a high-frequency shelving control, such as the UAD-1 Pultec.
Another thing to remember is that in the analog days, EQs like the Pultec, and those made by Neve, were chosen because of the specific quality of the “air” they imparted, which was based on their circuit design. Rule of thumb: try it with whatever EQ you have — if it sounds right, it is right.