What is a de-esser? 

A de-esser is a type of audio compressor that applies gain reduction to sibilance and other high frequency issues in a vocal track. Sibilances are high frequency sounds created by the human voice when pronouning the letters "s," "f," "s," "sh," and "ch." But, you can find these harsh high frequencies in other instruments as well, like crash cymbals and electric guitar. Sibilance and harsh frequencies typically happen anywhere between 4 and 10 kHz depending the the vocal and instrument.

How to use a de-esser to remove sibilance

1. Try level automation first

You can help to reduce the workload of your de-esser by attenuating sibilance with level automation. Manual de-essing requires you to identify sibilance and attenuate it manually by separating the clip and lowering the clip gain or by writing some level automation. This process can often sound more natural than other forms of de-essing, as you’re able to treat each sibilant sound individually. Basically, you look for the recognizable “ess” in the waveform—separate the "esses" into their own clip, and reduce the gain of that clip.

2. Insert a de-esser after EQ and compression

The drawback to manual de-essing is the amount of time it takes. A more common approach to removing sibilance is to use a dedicated de-esser plug-in that automatically reduces the level of harsh frequencies whenever they exceed a threshold.

Where do you put a de-esser on your vocal chain? Generally, it's a good idea to add a de-esser any time you hear sibilance in a vocal. Such as after additive EQ, or after adding reverb. 

Having a de-esser on your vocal after EQ and compression is especially important for controlling the unintended consequences of making the vocal cut through the mix. While compression and additive EQ tend to amplify sibilance, a de-esser will tame it.

Let's take a a look at a couple of de-esser options: Nectar's De-ess module and RX. 

Neutron 3 De-esser

To illustrate the effect of de-essing features, let’s take a look at some audio examples using audio content that you'd likely process with each of these tools. 

We’ll start with Nectar 3’s De-esser module, which we’ll use on a sung vocal recording. Then we'll use RX to edit a dialogue recording: 

We can hear that there are some problematic frequencies with the vocalist’s annunciation of the letter “S,” particularly around 0:05, 0:07, and 0:14. Here’s the same audio example using Nectar 3’s De-esser. Listen to how the esses become much less abrasive while still remaining audible, so the recording itself remains uncompromised:

RX de-esser

Next, let’s observe the effect of RX 7’s De-ess module on a spoken dialogue recording. Here’s the original audio file:

Once again, the harshness of the esses cuts through the rest of the recording’s sonic content. Now listen to the recording after it’s been processed with RX 7’s De-ess module in Spectral mode (more on the Spectral mode in a bit).

You may be noticing a pattern here: the goal is not to remove the esses altogether, but to reduce their presence just enough to eliminate harshness for your listeners. As the industry’s leading audio repair software, it’s no surprise that RX 7 does a fantastic job of mitigating the esses while retaining their natural audibility.

2. Focus the de-esser on the right frequencies

Now that you have a de-esser in your vocal signal chain, you'll want to focus the de-esser on harsh frequencies you want to attenuate. Nectar's De-esser module includes a detection cut off filter for adjusting the detection and reduction of sibilant frequency content. Any frequency content that is above the cutoff frequency will be used for De-esser detection.

Sibilances typically happen anywhere between 4 and 10 kHz depending the the vocal. So try focusing the frequency of the de-esser in that area. In general, sibilance in female voices occurs between 5–8 kHz and in between 3–6 kHZ in male voices.  

3. Decrease the threshold until you hear gain reduction 

Next, drop the threshold until the de-esser begins reducing the harsh frequencies caused by sibilance. Remember, you don't want to completely remove the "esses," since they're a normal component of human speech. Apply just enough gain reduction that the sibilance no longer sounds harsh to the listener.

4. Use multiple de-essers if necessary 

As we know from serial compression it’s often better to move the effectual needle one small process at a time, using many tools in series for a cumulative, more natural-sounding result, Often this approach beats using one plug-in in a heavy-handed manner.

This principle is especially true when de-essing. A little manual de-essing here—half a dB, maybe a dB—followed by some further de-essing of another decibel or two—with other processes between—is far more likely to get you a natural result without overcompressing the vocal and destroying its natural presence. 

5. Try de-essing reverb and distortion effects

If you’re planning on sending a little of your vocal to a reverb or a distortion effect, experiment with de-essing the vocal, even a second time, before hitting the verb or the exciter. A bright vocal may be too much for the reverb or the distortion process, calling too much attention to the onset of the ambiance or the harshness of distortion. Putting a de-esser before these processes can mitigate some of the unintended side effects.

6. Experiment with de-essers on other instruments

This is a bit of a bonus tip, but still, I’ll share it: de-essers are not just for vocals. Because of the innate harshness of many instruments—and because of the way some de-essers can respond quite smoothly—they can be great, band-specific remedies for guitars and drums, particularly overheads.

For guitars, this is especially true on electric axes that make use of amplifier simulators, as emulations often reveal their fakery in the harshness of the high-midrange. Slap a de-esser down around 4 kHz or so, and you may be able to get more authenticity out of a fake amplifier.

Likewise, if you have too much cymbal splash in the overheads—to the point that it’s just tearing your head off—give the de-esser a go. You may find it does the trick in softening the blow without sucking all the life out, as a static equalizer might.

Note: This video showcases these de-essing techniques using the De-ess module in RX 6. The same techniques are possible with other de-essers like the RX 7 De-ess module, which is largely identical to the De-ess module in RX 6.

Conclusion

In our efforts to master a technique, sometimes we apply de-essing where it’s not needed. Sometimes we overdo the process just to prove that we have a handle on it.

De-essing must be carefully employed; not all vocals require it.

Thus, along with this list of steps, always remember the context of what you’re de-essing. If you’ve spent an hour editing a vocal, give your ears a rest before mixing it, even if it’s just five minutes. If your vocal sounds good against a reference without the de-esser, maybe you don’t need it. Always remember that context is key in achieving your best ess.