Vocal Processors, And The Most Dangerous Knob On Them

If you were wondering, the most dangerous knob is the one that controls compression.

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The opinions expressed are mine only. These opinions do not necessarily reflect anybody else’s opinions. I do not own, operate, manage, or represent any band, venue, or company that I talk about, unless explicitly noted.

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Not every noiseperson is a fan of vocal processors.

(Vocal processors, if you didn’t know, are devices that are functionally similar to guitar multi-fx units – with the exception that they expect input to come from a vocal mic, and so include a microphone preamp.)

Vocal processors can be deceivingly powerful devices, and as such, can end up painting an audio-human into a corner that they can’t get out of. The other side of that coin is that they can allow you to intuitively dial up a sound that you like, without you having to translate your intuitive choices into technical language while at a gig.

What I mean by that last bit is this: Let’s say that you like a certain kind of delay effect on your voice. There’s a specific delay time that just seems perfect, a certain number of repeat echoes that feels exactly right, an exact wet/ dry mix that gives you goosebumps, and an effect tonality that works beautifully for you. With your own vocal processor, you can go into rehearsal and fiddle with the knobs for as long as it takes to get exactly that sound. Further, you don’t have to be fully acquainted with what all the settings mean in a scientific sense. You just try a bit more or less of this or that, and eventually…you arrive. If you then save that sound, and take that vocal processor to a gig, that very exact sound that you love comes with you.

Which is great, because otherwise you have to either go without FX, or (if you’re non-technical) maybe struggle a bit with the sound person. The following are some conversations that you might have.

You: Could I have both reverb and delay on my vocal?

FOH (Front Of House) Engineer: Ummm…we only have reverb.

You: Oh.

You: Gimme a TON of delay in the monitors.

Audio Human: Oh, sorry, my FX returns can only be sent to the main mix.

You: Aw, man…

You: Could I have a touch more mid in my voice?

[Your concept of “a touch more mid” might be +6 dB at 2000 Hz, with a 2-octave-wide filter. The sound-wrangler’s concept of “a touch more mid” might be +3 dB at 750 Hz, with a one-octave-wide filter. Further, you might not be able to put a number on what frequency you want, especially if what I just said sounds like gobbledygook. Heck, the audio human might not even be able to connect a precise number with what they’re doing.]

Sound Wrangler: How’s that?

You: That’s not quite right. Um…

[This one’s directly in line with my original example.]

You: Could I get some delay on my voice?

Audio Human: Sure!

[The audio human dials up their favorite vocal-delay sound.]

You: Actually, it’s more of a slap-delay.

[Your concept of slap-delay might be 50 ms of delay time. The audio-human’s concept of slap-delay might be 75 ms.]

Audio Human: How’s that?

You: That’s…better. It’s not quite it, though. Maybe if there was one less repeat?

[The audio-human’s delay processor doesn’t work in “repeats.” It works in the dB level of the signal that’s fed back into the processor. The audio-human takes a guess, and ends up with what sounds like half a repeat less.]

Audio Human: Is that better?

You: Yeah, but it’s still not quite there. Um…

Having your own vocal processor can spare you from all this. It also spares the engineer from having to manage when the FX should be “in” or bypassed. (This often isn’t a huge issue, but it can become one if you’re really specific about what you want to happen where.) There are real advantages to being self-contained.

There are negative sides, though, as I alluded to earlier. Having lots of power at your disposal feels good, but if you’re not well-acquainted with what that power is actually doing, you can easily sabotage yourself. And your band. And the engineer who’s trying to help you.

EQ Is A Pet Dog

The reason that I say that “EQ is a pet dog” is twofold.

1) EQ is often your friend. Most of the time, it’s fun to play with, and it “likes” to help you out.

2) In certain situations, an EQ setting that was nice and sweet can suddenly turn around and “bite” you. This isn’t because EQ is “a bad dog,” it’s because certain equalization tweaks in certain situations just don’t work acoustically.

What I’ve encountered on more than one occasion are vocal-unit EQ settings that are meant to either sound good in low-volume or studio contexts. I’ve also encountered vocal-unit EQ that seems to have been meant to correct a problem with the rehearsal PA…which then CAUSES a problem in a venue PA that doesn’t need that correction.

To be more specific, I’ve been in various situations where folks had a whole busload of top-end added to their vocal sound. High-frequency boosts often sound good on “bedroom” or “headphone” vocals. Things get nice and crisp. “Breathy.” Even “airy,” if I dare to say so. In a rehearsal situation, this can still work. The rehearsal PA might not be able to get loud enough for the singer to really hear themselves when everybody’s playing, especially if feedback can’t be easily corrected. However, the singer hears that nice, crisp vocal while everybody’s NOT playing, and remembers that sound even they get swamped.


The problem with having overly hyped high-end in a live vocal (especially with a louder band in a small room) is really multiple problems. First, it tends to focus your feedback issues into the often finicky and unpredictable zone of high-frequency material. If there’s a place where both positionally dependent and positionally independent frequency response for mics, monitors, and FOH speakers is likely to get “weird” and “peaky,” the high-frequency zone is that place. (What I mean by “positionally dependent” is that high-frequency response is pretty easy to focus into a defined area…and what THAT means is that you can be in a physical position where you have no HF feedback problems, and then move a couple of steps and make a quarter turn and SQUEEEEAAALLL!)

The second bugbear associated with cranked high-end is that, when the vocals are no longer isolated, the rest of the band can bleed into the vocal mic LIKE MAD. That HF boost that sounds so nice on vocals by themselves is now a cymbal and guitar-hash louder-ization device. If we get into a high-gain situation (which can happen even with relatively quiet bands), what we then end up doing is making the band sound even louder when compared to your voice. If the band started out a bit loud, we may just have gotten to the audience’s tipping point – especially since high-frequency information at “rock” volume can be downright painful. Further, we’re now spending electrical and acoustical headroom on what we don’t want (more of the band’s top end), instead of what we do want (your vocal’s critical range).

Now, I’m not saying that you can’t touch the EQ in your vocal processor, or that you shouldn’t use your favorite manufacturer preset. What I am saying, though, is that dramatic vocal-processor EQ can really wreck your day at the actual show. You might want to find a way to quickly get the EQ bypassed or “flattened,” if you can.

“Compression” Is The Most Dangerous Knob On That Thing

Now, why would I say that, especially after all my ranting about EQ?

Well, it’s like this.

An experienced audio tech with flexible EQ tools can probably “undo” enough of an unhelpful in-the-box equalization solution, given a bit of time. Compression, on the other hand, really can’t be fully “undone” in a practical sense in most situations. (Yes – there is a process called “companding” which involves compression and complementary expansion, but to make it work you have to have detailed knowledge of the compression parameters.) Like EQ, compression can contribute to feedback problems, but it does so in a “full bandwidth” sense that is also much more weird and hard to tame. It can also cause the “we’re making the band louder via the vocal mic” problem, but in a much more pronounced way. It can prevent the vocalist from actually getting loud enough to separate from the rest of the band – and it can even cause a vocalist to injure themselves.

Let’s pick all that apart by talking about what a compressor does.

A compressor’s purpose is to be an automatic fader that can react at least as quickly (if not a lot more quickly) as a human, and that can react just as consistently (if not a lot more consistently) as a human. When a signal exceeds a certain set-point, called the threshold, the automatic fader pulls the signal down based on the “ratio” parameter. When the signal falls back towards the threshold, the fader begins to return to its original gain setting. “Attack” is the speed that the fader reduces gain, and “release” is the speed that the fader returns to its original gain.

Now, how can an automatic fader cause problems?

If the compressor threshold is set too low, and the ratio is too high, the vocalist is effectively pulled WAY down whenever they try to deliver any real power. If I were to set a vocalist so that they were comfortably audible when the band was silent, but then pulled that same vocalist down 10 dB when the band was actually playing, the likely result with quite a few singers would be drowned vocals. This is effectively what happens with an over-aggressive compressor. The practical way for the tech to “fight back” is to add, say, 10 dB (or whatever) of gain on their end – which is fine, except that most small-venue live-sound contexts can’t really tolerate that kind of compensating gain boost. In my experience, small room sound tends to be run pretty close to the feedback point, say, 3-6 dB away from the “Zone of Weird Ringing and Other Annoyances.” When that’s the case, going up 10 dB puts you 4-7 dB INTO the “Zone.”

But the thing is, the experience of that trouble area is extra odd, because your degree of being in it varies. When the singer really goes for it, the processor’s compressor reduces the vocal mic’s gain, and your feedback problem disappears. When they back off a bit, though, the compressor releases, which means the gain goes back up, which means that the strange, phantom rings and feedback chirps come back. It’s not like an uncompressed situaton, where feedback builds at a consistent rate because the overall gain is also consistent. The feedback becomes the worst kind of problem – an intermittent one. Feedback and ringing that quickly comes and goes is the toughest kind to fight.

Beyond just that, there’s also the problem of bleed. If you have to add 10 dB of gain to a vocal-mic to battle against the compressor, then you’ve also added 10 dB of gain to whatever else the mic is hearing when the vocalist isn’t singing. Depending on the situation, this can lead to a very-markedly extra-loud band, with all kinds of unwanted FX applied, and maybe with ear-grating EQ across the whole mess. There’s also the added artistic issue of losing dynamic “swing” between vocal and instrumental passages. That is, the music is just LOUD, all the time, with no breaks. (An audience wears down very quickly under those conditions.) In the circumstance of a singer who’s not very strong when compared to the band, you can get the even more troublesome issue of the vocal’s intelligibility being wrecked by the bleed, even though the vocal is somewhat audible.

Last, there’s the rare-but-present monster of a vocalist hurting themselves. The beauty of a vocal processor is that the singer essentially hears what’s being presented to the audience. The ugliness behind the beauty is that this isn’t always a good thing. Especially in the contexts of rock and metal, vocal monitors are much less about sounding “hi-fi” and polished, and much more about “barking” at a volume and frequency range that has a fighting chance of telling the singer where they are. Even in non-rock situations, a vital part of the singer knowing where they are is knowing how much volume they’re producing when compared to the band. The most foolproof way for this to happen is for the monitors to “track” the vocalists dynamics on a 1:1 basis – if the singer sings 3 dB louder, the monitors get 3 dB louder.

When compression is put across the vocalist immediately after the vocal mic, the monitors suddenly fail to track their volume in a linear fashion. The singer sings with more power, but then the compressor kicks in and holds the monitor sound back. The vocalist, having lost the full volume advantage of their own voice plus the monitors, can feel that they’re too quiet. Thus, they try to sing louder to compensate. If this goes too far, the poor singer just might blow out their voice, and/ or be at risk for long-term health issues. An experienced vocalist with a great band can learn to hear, enjoy, and stop compensating for compression…but a green(er) singer in a pressure situation might not do so well.

(This is also why I advocate against inserting compression on a vocal when your monitor sends are post-insert.)

To be brutally honest, the best setting for a vocal-processor’s compressor is “bypass.” Exceptions can be made, but I think they have to be made on a venue-to-venue, show-to-show basis.

All of this might make it sound like I advocate against the vocal processor. That’s not true. I think they’re great for people in the same way that other powerful tools are great. It’s just that power tools can really hurt you if you’re not careful.