An RTA (Real Time Analyzer) is a tool that most of us have used at some point in our audio careers. The proliferation of software-style RTA’s on phones, tablets and computers have made them ubiquitous. Practically every engineer has an RTA in their pocket, or at least has one close by. Although I feel that RTA’s are an invaluable tool for any audio engineer, I’ve also spent many years listening to people knock the use of RTA’s using that old refrain of “we never had RTA’s back when I was learning sound” or “don’t use an RTA, use your ears.” In fact, a simple RTA can be a very useful tool if you understand what influences its measurements and what its limitations are.
Connecting an RTA to Your System
I know what you’re thinking…. “I don’t connect my RTA to my system at all. I pull my phone out of my pocket and open the RTA app.” If you are just doing basic tasks or taking low-resolution measurements, then simply using your phone’s internal microphone as the source signal for your RTA app is sufficient.
However, there may come a point when you want a more substantial RTA than what is built into your phone. It may be that you want a larger display that’s visible the entire time you’re mixing. Or it may be that you want more control over how the RTA is displaying information. Once you branch out beyond the simple phone RTA app, either to a hardware RTA or a software-based RTA on a laptop, you may need to connect directly to your system.
When mixing FOH, an RTA is often fed from either a dedicated measurement mic or directly off of the console’s stereo bus. When fed from a measurement microphone, keep in mind that your room acoustics will influence your measurements considerably. When mixing monitors, the most common RTA connection point is from your cue bus. This way, whenever you solo a monitor mix, that mix is fed to your cue wedge as well as your RTA.
Hardware vs. Software
As recently as 10 or 15 years ago, hardware RTAs were the only thing that was available to the average audio engineer, so that’s what was used. They were a mainstay in monitor EQ racks and FOH drive racks. At one time, few people owned laptops and there were even fewer smartphones. I did a bit of searching around and I can’t seem to find anyone who makes a hardware RTA in 2016. They have simply been replaced with computers and smartphones. A basic software RTA can be had for free on every smartphone platform or computer operating system. One of the great benefits of free software RTAs is that everyone can have one. As an audio teacher, this has proven very valuable for me, because in fact, an RTA is an amazing basic training tool for up-and-coming engineers. Using an RTA when ringing out monitors is the first step to training your ear to identify and eliminate feedback, for example. Software RTA’s also give us a lot of features that were never found on their hardware counterparts, such as the ability to adjust the resolution, set peak-hold times, or change the averaging time to slow down or speed up the response.
Inherent Limitations
An RTA is a basic audio measurement device that shows you two parameters about what’s happening with your system: Amplitude and Frequency. That is to say, an RTA is a two-dimensional measurement device. Amplitude is shown on the vertical axis and frequency is shown on the horizontal axis. While this information is very useful in certain applications, there is some missing information that is critical when making equalization decisions. An RTA does not show us anything about phase or time, which is a critical parameter when tuning a sound system. This means we cannot set time alignment delays using an RTA, nor can we directly see the influence of acoustic reflections on our measurements.
If its inherent limitations are understood, an RTA can be a useful tool, but if these limitations aren’t understood, you can spend a lot of time chasing your tail and equalizing things that can’t be corrected with EQ in the first place. Furthermore, there is a tendency to want to tune every speaker “flat” using an RTA. Unfortunately, “flat” doesn’t always sound subjectively “good,” nor is it possible to reliably tune a system flat with an RTA because of the lack of phase information. The bottom line is, don’t make critical system tuning decisions using an RTA. Instead, use an RTA for quickly and easily identifying feedback frequencies or getting a general sense of the balance of energy in your mix.
In 2016, an RTA is somewhat of a dying breed. In fact, it has been a dying breed for quite some time. The price of dual-channel FFT analyzer software has come down so far that it’s within reach of any working engineer. Such software can be had for far less than a hardware RTA just a decade ago.
That said, an FFT analyzer, while an indispensible tool, still makes for an expensive RTA. If you only plan to use the RTA functionality, go find something for free online. Keep in mind, however, that if you really want to make serious, critical three-dimensional measurements of a sound system, an RTA might not be the right tool for what you’re trying to do.
Vince Lepore is the technical director at St. Luke’s United Methodist Church in Orlando and teaches live production at Full Sail University.
