Reading the Data Correctly?

I will take you on a multipart excursion and discuss the background principles of acoustical measuring tools. Since only so much will fit onto one page, this will become a multiple-part trip. I would appreciate your patience with the more broad statements at the start. I read a few years back that leaders of society felt that the availability of information was what would help society progress faster. Now with everything available at all times through a gazillion web pages and the arrival of the internet, we now know that the availability of information alone was not the key to progress. The most searched items on the web are porn related, with a steep fall to the next most searched item!

When I started in this industry some 35 years ago, having any tool other than your trained ears was a luxury, and then the results of the available tools were rather rudimentary. For me, this changed with the arrival of MEYER SOUND’s SIM and APOGEE SOUND’s CORREQT in the late ’80s. I was lucky to be trained on CORREQT, and as a consequence, I later on invested a fortune to buy an early-stage FFT analyzer and the associated dedicated Mic Switch and a bunch of Delay units. In my case, this was an HP (Hewlett Packard) 3582; at that time, this was the machine used by both loudspeaker brands before SIM became a self-contained analyzer tool. At that time, a full-fledged system for measurements would cost you close to 50,000 US Dollars, and this was before all the inflation of 40 years, so this was a small fortune to spend.

When you want to use such a machine successfully, you must undergo training and understand how to read the screen correctly. Along the course, you would typically also realize that the wrong settings on the machine will create useless data, leading to stupid decisions on your tuning devices. The correct measurement system setup was mission-critical, and you learned this during training. How does all this look and work today? It is almost impossible to imagine any serious size event FOH without a screen that shows an analyzer tool and offers some SPL reading during the show. And today’s tools also do not cost a fortune anymore; some are shareware and free items to download and use. A complete system of software solutions, audio Interface and measurement microphone can start anywhere at 500 USD today. More sophisticated systems are available for around 1,000 USD, far from a fortune. However, since all this is so affordable and as long as your screen shows a nice colourful picture, it seems that not too many people are clear on what they are looking for and what they are looking at when using those pieces of software. Still, those colourful screens are very popular nonetheless. This is like when at a younger age, you want to wear certain clothing to be considered part of a specific group of people you aspire to belong to.

At the same time, the tools get developed further and offer more data with each new release. I wonder if user education comes along at the same speed as the product feature set; consequently, a lot of data is not interpreted correctly. In the course of this discourse, I will raise a few things for you to go out and learn and build your own opinion. Let’s start with the hardware to ensure we have a good base level. A 50 USD measurement microphone will not give you the same details as a 3,000 USD unit. You might not need the expensive unit, but your spending on this hardware will impact you. The same is valid for the audio interface, so why would you expect to tune a 250,000 US Dollar PA with a 50 US Dollar piece of testing hardware? The quality of the Mic Preamp in your audio interface directly impacts the resolution of your measurement results. I am aware that with modern measurement systems, a Signal to Noise of 12db or more is already sufficient to consider the measurement valuable since we primarily measure relatively. You need to at least be aware of the limitation of any gear in your setup to avoid wrong and possibly disastrous decisions on your system tuning. I will elaborate on the importance of the mic and interface next month.

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Alex. Alex can be reached at alex@asaudio.de