Advanced EQ techniques

EQ also can be used as a corrective measure. The techniques described in the preceding sections aimed to improve the overall sonic quality of your audio by focusing on what you wanted to be heard. You also can use EQ to remove extraneous noise that you don't want in the file.

Clearing up noise
If you recorded your audio in a noisy environment, you can use EQ to get rid of some of the worst noise. First, roll off all the low frequencies. You should do this regularly to all frequencies below 60Hz, because they're generally not reproduced by most systems. You can roll off more if you're dealing with serious noise. For example, traffic outside a busy city window will be audible as a steady low rumble, with the occasional siren or horn. If you roll off more of the bottom end, the sound of the traffic will be less audible.

Similarly, you can roll off high frequencies if you have noise problems such as air conditioning or tape hiss. In the preceding example, we boosted all frequencies above 5KHz to give the file some air; clearly, this is not something we'd want to do if we were in a noisy environment. Of course, we could have used the shelf to roll off all high frequencies above 8KHz or so and added a slight lift around 4–5KHz. Very little important voice information is in the range above 10KHz, so if you have noise problems, you can safely roll this off without any damage to the intelligibility of the audio.

Of course, in extreme situations, you can get pretty savage with EQ if necessary. For example, sometimes news reporters outside during a storm sound like they're talking through a telephone line. This is because the audio engineer at the station has rolled off all low frequencies and high frequencies, leaving just the mids.

Pops
Sometimes, a pop sneaks into your audio file, even if you're using a pop screen. If you zoom in to your audio file and look at the offending pop, you'll see that it's a very brief, very loud low frequency burst. You can highlight the offending word (or even syllable) and roll off the offending bass frequencies, as shown in Figure 1.


Figure 1: A pop is visible as a short, loud low-frequency burst, which can be fixed with EQ.

Experiment with different amounts of roll-off at different frequencies. You'll find that if you roll off too much, you get rid of the pop, but the result may sound unnatural. Find a good balance between removing as much of the offending pop as possible, while retaining the natural feel of the original.

Dealing with sibilants
Some people have a problem with sibilants, which are consonants like the letter "s" ("d" and "t" can also be a problem but usually nowhere near as much) that contain a burst of high-frequency information. This is audible as a whistling or, well, an "ess" sound. A little of this is natural, but too much is annoying. Some people actually whistle when they pronounce these consonants, which is an extreme version of the same problem. Because this is usually a very localized problem, it can be dealt with using EQ.

Sibilants usually are most prominent around 5KHz. Just like the preceding example where a word was highlighted and bass frequencies were rolled off to get rid of a pop, you can highlight a word and try to cut the offending frequency. Dealing with sibilants is more troublesome than popping, because our ears are very sensitive to high frequencies, and even if it's only a momentary change, our ears may notice that the sound has changed. Not only that, but if someone has trouble with sibilants, it usually manifests itself throughout the entire interview — and the letter "s" is very popular in the English language. In general, if you want to deal with sibilants, you should use a de-esser. That's a fancy term we audio engineers made up to describe a "frequency dependent, side chain controlled compressor." De-essers are explained in the compression section, which comes next.