Tag Archives: Time

The Off-Axis Guitar Conundrum

When you point the guitar amps off-axis to fix an SPL and magnitude response problem, you will often incur a time problem.

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I’m sure that I’m not the only small-venue guy who has ever ended up chasing their tail in terms of how guitars sound in the room. Not too long ago, I did a show where the guitars were a bit much for the room. We ended up pointing both amps at the stage-right wall, which had some acoustical treatment on it.

This helped a fair bit, in terms of cutting a dB or two off the overall volume and alleviating the “guitar screech” issue. What it also did, though, was remove a lot of the articulation from the guitars – to the point that, with the band playing, I knew the guitars were “loud enough,” and yet I couldn’t really hear what they were doing. This was something I’ve experienced before, but this time, it really started to bug me.

“Why,” I thought to myself, “is the guitar sound at this gig kicking my butt so hard?”

The good news is that I think I have an answer.

Starting At The Beginning

When it comes to high(er) frequencies, guitar amps are directional creatures (like just about everything else.) If you apply the ol’ standby, wavelength = velocity/ frequency, you start to see why. At, say, 2500 Hz, the wavelength is roughly five and a half inches. This is rather smaller than the diameter of a 12″ cone – 12″ cones being very common in guitar world. Since the wavelength is smaller than the cone, the cone is able to impart a good amount of directivity to that frequency, as well as just about everything above 1250 Hz or so. As a result, the guitar rig tends to “beam,” or throw high frequency content in a concentrated pattern.

And that’s just the first bit.

There are a good number of guitar speakers that have a sizeable “bump” from about 2 kHz to 4 kHz. Here’s a graph I created from data for the Eminence “Red, White, and Blues” loudspeaker:

Not all guitar speakers exhibit this kind of response, but it’s easy to run into drivers that do. There are a LOT of ’em that exhibit some variation of the “high-mid hill” that you can see in the graph.

Here’s the rub.

Those response peaks often live in the most *!@#%^& annoying parts of the audible spectrum. Seriously. Infants cry in that range because it really, really, REALLY gets the attention of everyone around them. It’s impossible to ignore. It sounds like someone is running a drill inside your ear canal.

…and there are guitar-cab drivers where the “baby-cry peak” is 8 dB higher than everything else in the spectrum. That’s a bit more than six times as intense.

So, you’ve got yourself a device that’s very good at making irritating frequencies, good at focusing those frequencies into a small dispersion area, and (usually) lacks the kind of surgical tone control necessary to fix the screech.

This is what was happening to me at the gig.

Surgery With A Sledgehammer

As an audio human, I am rarely invited to “turn the knobs” on the guitar amps. In this case, though, I had an opportunity with one of the rigs in question.

I rolled the mids down.

Nope, not in the right place.

I pulled the highs back.

Okay, but I was killing the top end entirely by the time the screech was under control.

Most guitar-amp tone stacks use “wide” filters. As a result, you end up affecting a whole bunch of frequencies when you start flipping those knobs around, not just the octave or so that you really want to tame. It’s like doing neurosurgery with a meat cleaver – you cut out your problem area, but you lose half the brain in the process.

In the end, I was able to settle on a spot for the highs that wasn’t total mud, and yet did also help with the screech. It wasn’t a fix, but it was something.

The other amp’s screech factor was rather less pronounced, and I wasn’t in a position to be futzing with the knobs on that rig, so now it was time to step back and assess.

We still needed to take the edge off.

With no more tone-stack solutions to be had, it was time to start pointing the amps in different directions. Initially, we had one amp pointing at the stage-right wall, and the other pointing at the downstage left corner. This sounded pretty good.

Of course, the bartender was getting HAMMERED by the not-terrible-but-still-prominent “screech zone” on the amp pointing his way. We subsequently ended up with both amps being pointed (to different degrees) at the stage-right wall. The overall level was high-ish, but manageable.

…and like I said, I could hear that the amps were loud enough, and yet I couldn’t really make out what the guitarists were doing when everything else was “in play.”

The Breakthrough

At some point, I had to “get on the gas” to put a guitar solo in the right place.

Suddenly, everything clicked. The guitar was in the right place, level wise, and it also had articulation and clarity. It was like a ton of bricks had been dropped on me.

See, the whole time, I was thinking that the issue was a frequency magnitude issue. I figured that, by pointing the amps at the wall, we had killed off so much HF information that the guitars were indistinct due to mud. Sure, there was a lot of low(er) frequency information flying around, but the guitars still had a fair amount of other material to balance it.

The breakthrough came when I overcame the lead guitar, through the PA, and hit a level that was pretty healthy when compared to the stage wash. The PA sound had been heavily band-limited – meaning I had chucked out a lot of LF AND HF information. I realized that the HF content wasn’t the sole, deciding factor.

We had a time problem. That time problem disappeared when the PA took over the sound, because the PA was delivering direct, un-reverberated audio to the dance-floor. The transients were “clean,” even if their HF information had been drastically lopped off.

A lot of audio techs, myself included, tend to fall into the trap of looking at everything as a frequency magnitude issue. Not enough highs, too much low end, mids in the wrong place, whatever. It’s easy to get into this mindset, because we have very powerful tools for fixing frequency magnitude problems. My “go to” EQ plugin is a fully parametric powerhouse with as many bands as the computer can handle. I love it.

But it can’t fix time problems.

The issue with the guitars was that, for all intents and purposes, the audience and I were listening to only the reverberant field. Instead of having a good amount of nice, clean “direct impulse” from the amps, we were mostly listening to audio that had bounced off a wall (or several) before it had ever arrived at us.

Next chance you get, take a pristine vocal track and put it through a reverb that simulates a lot reflections – early and late. Make it wet. REALLY wet. Pretty tough to figure out what the person is saying or singing, isn’t it? Individual notes are kinda hard to place, aren’t they? Sure, the magnitude response has changed, but a huge factor in being able to figure out what’s going on in music is being able to perceive where notes start and end. That’s a LOT harder to do when all the transients are getting smeared around like warm peanut butter.

We had fixed our frequency response problem, but we had precipitated a massive time-smearing issue in the process. Sure, it wasn’t like we were in a cathedral (this is The SMALL Venue Survivalist, after all), but all the reflections involved in the audio were not subtle. At all.

So – audio-techs: Be aware that time is an issue for you. Be aware that solving time problems, especially complex ones (like how something is interacting with the reverberant field) often involves making physical changes to things. Changes to the room. Changes to instrument placement and amplifier direction. You have to physically touch things, and make stage layout choices to the degree that you’re empowered to do so. Sure, you can fix basic alignment problems with a delay line, but everything else pretty much requires fixing things at the source.

Musicians: Be aware that time issues have an effect on the sonics of your show. Especially if you’re a guitar player, and you play in small venues a lot, try to pick gear that sounds good when directed at the audience, so that time smear can be minimized – or, pick gear that can have its major mix contribution come from the (hopefully) smoothly responding and rather more directive PA gear. Reducing the overall stage volume of the entire band can help with this.

In general, I would suggest that what we want to deliver to an audience is sound that is balanced, free of irritating magnitude response spikes, and is only influenced by the venue’s reverberant field to a degree that we have intentionally chosen.