Handheld Quantities

There is a tendency in the sound reinforcement business to assume that if the system sounds OK, then measurements to quantify the performance are redundant. However, quantifying (by measurement) the sound reinforcement system performance can show up defects that may only be noticed by someone seated right in front of the left FOH stack or in the balcony, house right. You can save a lot of steps by checking the performance of each path in the signal chain at the rack, to be sure that excess noise (between acts) and distortion (at full volume) doesn’t appear in any of the subsystems.

There was a time when knowing exact values for sound system performance required rolling in equipment cases full of measurement gear. These days there are some excellent measurement tools that fit in the palm of your hand. You still need the bigger stuff to do detailed measurement and documentation but to quickly quantify the basic electronic performance of the system, these handheld tools are excellent.

The well-known test gear from Audio Precision; Hewlett-Packard; Neutrik (NTI); Rohde & Schwarz; Stanford Research Systems; Tektronix; and others, are good for shop testing and major installation work. These units provide the kind of detailed analysis needed to quality a new sound system installation. However, there are much smaller units that are better suited to performing troubleshooting tasks and a quick check of “the specs” onsite. Of course, to document the measurement results, these larger units provide data formatted to connect directly to printers, while you may find a digital camera is the most convenient way to document results from a handheld unit.

A handheld analyzer that can provide signal-to-noise, distortion, relative and absolute level, 1/3-octave spectrum analysis and polarity will suit many electronic field testing needs. These are electronic measurements (from microphone output to loudspeaker input) of analogue audio and should not be confused with the acoustical measurements of sound in the air between loudspeaker and the listener/microphone. The acoustical measurements require specialized instrumentation to gather accurate information about the direct sound (without late reflections and reverberation) that is important to sound reinforcement loudspeaker systems. A conventional RTA (real-time analyzer) is not recommended (indoors) in setting loudspeaker EQ.

These new handheld analyzers allow you to make quick and accurate measurements within equipment racks, at the end of loudspeaker lines or at the mixing console. Not only can you read the level of background noise, distortion and frequency response; you can also examine the spectrum and waveform to look at the nature of the signal. It is far more informative to know the spectrum of noise and distortion artifacts when assessing their audibility or troubleshooting their cause. You can pull one out of the toolkit and have a reading within 30 seconds. They are small enough to fit in a tool belt; so they can be with you reach the top of the ladder and battery power keeps these units from creating ground loops.

I have used two units extensively in field work: the Audio Toolbox from Terresonde; and from Neutrik Test Instruments (NTI), the Minilyzer® ML1 along with its companion the Minirator® MR 1. Each of these units has unique capabilities and individual strengths. The Audio Toolbox is available in several variations, including a specialized version for the A/V integrator from Sencore, called the SP295 SoundPro Audio Analyzer. These units share the same basic functionalities and each unit includes the generator and analyzer (including a microphone) in a single package. The Audio Toolbox goes well beyond just audio testing to provide other functions, including MIDI and SMPTE timecode generation and analysis. The smaller NTI units focus strictly on audio signals and use two separate devices for generating test signals (MR 1) and analysis (ML1). This has the advantage of allowing you to input the signal at one end of the signal chain and then measure the signal at remote locations. A real cable saver when dealing with systems that have components spread around the venue. More info is available on these handy analyzers at the company web sites: www.terresonde.com, www.sencore.com and www.nt-instruments.com.

If you also have digital audio signals running through your sound system, there are handheld analyzers that can give you insight into that signal path. Two that fit into you hand, and are focused on the increasingly common AES/EBU signal interconnections, are the Prism Sound DSA-1 (www.prismsound.com) and the Tektronix AM70 (www.tektronix.com). These units will bring your troubleshooting up-to-date. The next step is the handheld data monitoring and analysis tools for checking those Ethernet and IEEE 1394 connections that are gathering momentum in audio signal transmission.

All of these handheld analyzers may be handy and invaluable troubleshooting tools, but with the growth of alternatives to analogue audio signal interconnections, soon we may find our hands are full of these little tools.

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