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A Tuning “Standard”? A Discussion Of System Performance Consistency

After the “right” system has been selected for an event, do mix engineers have any guarantee that they can begin the day’s work from a neutral starting point?
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As audio mixers and engineers, we live in a world of standards. With the oversight of the Audio Engineering Society (AES) and many other vital and committed organizations, there’s a solid foundation of standards that help us make many of the decisions in our daily audio lives.

When specifying a sound system for a show, we can look at a lot of information to help decide what type of design/approach is most suited for the venue, budget and application. These decisions are derived, in part, with the assumption that the information on loudspeaker coverage, power amplifier performance and other parameters is accurately reported by the manufacturers, allowing us to weigh the options based on the expected performance level of a system with those technical specs.

But after the “right” system has been selected for an event, does the mix engineer who will be mixing on it have any guarantee that he/she can begin the day’s work from a neutral starting point? A sound company committed to quality and an experienced system tech will ensure the firmware and software is current, and that all of the components are functioning properly, before presenting the system to the mix engineer as a starting point.

A scenario where this is very important is festivals. Many bands and engineers may be using the same system that day, and often there isn’t the opportunity to spend time “tuning” by listening to music, or sound checking before hopping behind the console. It’s becoming more and more common for engineers to bring their show files to load into the festival’s digital consoles, and the tonality differences between each mix can vary widely as each engineer’s “home” system may be tuned in a very different way.

Level Of Expectation

Wouldn’t it be great if mix engineers and system techs could agree (with a small degree of deviation) on what they’d like to see as a “standard tonality” for a system that has been optimized, tuned, and deemed ready? We all have our own unique approach, and I’m not suggesting that every system out there should be tuned in exactly the same fashion, but it’s a great topic that I’d like to encourage more dialog on.

On many tours, the engineer and tech work together to achieve the results they’re seeking, with the band’s and/or manager’s approval being the final say. Some engineers with unorthodox gain structure and input channel treatment might choose to have the system tonally balanced much differently than another engineer who follows more traditional methods.

But I believe this kind of “tuning the system to fit the mix” approach is best used in a touring setting, where the system is theirs to do as they please, and not necessarily for multi-act shows where several engineers have to work on the same system in one day. Whether they’ve brought their own show file along or are just going to “spin up a mix” from scratch, I believe there should be some level of expectation as to the tonality of the PA.

However, what that “standard” tonality should be is the question. There are many different views on this topic, so let the discussion begin, but I believe the answer lies somewhere between what our ears tell us and what the transfer function reading tells us when the system is measured.

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Screenshot of Smaart v8 transfer function.

When we use one of the fine computer/software-based measurement tools available to us these days, such as Rational Acoustics Smaart and Meyer Sound SIM, the transfer function measurements that show the system’s frequency response are very useful.

If the measurement system is set up correctly and utilized as instructed by a competent system tech with lots of experience, we can use the transfer function to compare the source material (music, pink noise) coming from the console to a reference microphone’s reading in the room. If we achieve a flat transfer function, the system’s response is relatively the same as what is coming out of the console. In essence, if the console mix sounds good, so should the PA.

A flat transfer function would be the “clinical proof” that the system is balanced from the lows up through mids and highs. Our ears would tell us if this is personally pleasing, and this would be then be the starting point to deliver our mixes.

Neutral Or Tilted?

There are different schools of thought on a starting point for a system. With a flat transfer function from 20 Hz to 20 kHz, we may find that our mix sounds a little thin, so many engineers (including myself) mixing rock or pop music will agree that the level of the sub bass and low-frequency section should be turned up or “tilted” by some degree to sound the way we like it: full and round.

However, a flat frequency response from 200 Hz or so all the way up to 20 kHz should produce good initial results throughout the rest of the spectrum. Again, the point here is that the “standard” set by this flat response is that the system sounds like the console, so if you have that side of things sorted, the PA should produce a good neutral “canvas” for your artistic masterpiece.

It’s worth noting that other styles of music, such as classical and jazz, can be well suited to a completely flat transfer function. So too can spoken word and corporate speech-based content, with an aux send of music/video roll content only to avoid an excess of low-frequency energy that can mess with lavalier or headset mics.

Getting back to festivals, I recall a day many years ago when I was the FOH engineer for one of the six bands on the bill for a festival in the Boston area. We were in slot five, so as we were backstage readying our backline gear on risers and miking up, I was able to hear several bands performing before us.

As the first band was introduced, a long, howling low-end stream of feedback rung out for at least 10 seconds before the engineer was able to right the ship. Things were still unstable in the lows for a couple more songs, and then it started to shape up. When the second band fired up, the exact same thing happened. Then the third, and also the fourth. Something seemed very wrong.

Solid Starting Point

When I finally had my chance to get out front and “prep” my console for the show (this was one of those days when I had to spin it up from scratch on an analog console with no line check in the PA), I made a very conscious decision to roll all of the high-pass filters (HPF) on the input channels up much higher than I normally would – I often run vocal HPFs between 160 Hz and 200 Hz based on the way I tune my systems (which, as noted above, is flat response from 200 Hz to 20 kHz with a 12 dB boost in the sub centering around 60 Hz).

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Getting back to this particular show, however, I started at a very “safe” 300 Hz or so, and even engaged some HPFs on inputs I normally leave untouched, such as floor toms and bass guitar. When we began, I was absolutely stunned that the same low-end rumble started right out of the gate for me too.

It took a little while to roll those HPFs up even higher and to do some cutting on the system EQ, but when I finally had a chance to catch my breath, I turned to the festival system tech for the day, and in as kind of a manner as I could muster said, “You have got to be kidding me!”

Afterward, I had a chance to talk to the house audio personnel, asking who tuned the PA as well as how much were the subs and lows turned up in comparison to the mids and highs. They just kind of shrugged in response, because the answer was pretty obvious: way too much.

So the next time you’re in a situation where you’re mixing a show on a system that you haven’t had a chance to hear prior to putting the mix through it, ask yourself this: “What starting point would I like if given the choice, and could we possibly agree that we could all benefit from more dialog in the audio community regarding a standard tonality for multi-act festival shows moving forward?”

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