The Reverb Decay Time function computes the reverb decay time for a room, referenced to RT60. The full-band (20 to 20k Hz) flat measurement is actually extrapolated to find the RT60 value, since a full 60 dB of S/N ratio is often not available (a minimum of 30dB S/N is recommended). The Decay Time field displays the actual time (in milliseconds) for the sound field to decay by the displayed Decay Range amount.

Energy Time Graph screen	Real-Time Analyzer screen at 1¼12 octave resolution	Sound Pressure Level Meter screen

The Polarity Tester function is worth its weight in gold—a decent tester costs $250 to $300 alone—and I can’t tell you how many times I’ve found studio speaker components out of phase! Toolbox lets you test mics, patchbays and anything else in the studio with an innie and outie. Since it’s tethered to a cable, the one-piece unit can be a bit restrictive when “popping” speakers, but this is a minor inconvenience. If you have older gear, remember that Toolbox is a pin-2 positive unit. Three separate setups are programmed into the polarity tester for testing speakers, microphones and line-level equipment. A signal strength meter lets you adjust volume levels to get a good reading (most other testers can give false readings at improper levels).

The Noise Criteria function is used to determine the background noise level in a room, according to ANSI specification S12.2-1995. In operation, the room noise is divided into octave-band divisions, and the acoustic level of each band is computed in dB SPL. Then, the results are compared to standard noise criteria curves and a single value is determined from the highest curve number that any octave band exceeds. Also, the Speech Interference Level (SIL) can be computed. This value is the average dB SPL level of four octave bands centered on 500 Hz, 1 kHz, 2 kHz and 4 kHz. SIL is also defined in the ANSI standard that specifies Noise Criteria. These functions don’t mean much to the average studio owner but are necessary for comprehensive field measurements.

TEST FUNCTIONS
The Test Functions submenu offers Signal Generator, Level Meter/Frequency Counter, Signal-to-Noise Ratio, Sweeps, Sample Scope and a Distortion Meter.

The Signal Generator offers a control surface for acoustic measurement programs and creates waveforms used in testing, audio analysis or recording. Output levels for sine and square waves, white noise and pink noise can be adjusted in fine and coarse modes, while the unit displays the actual output level present, including loading from the device connected to the outputs. A Polarity Waveform feature lets users test polarity within a circuit; an Impedance Meter function is also provided.

The auto-ranging Level Meter accurately measures the level for both inputs simultaneously. Four submenus are available: a stereo audio level meter, a stereo frequency counter, a stereo dB meter and a stereo VU meter. The signal level units may be selected from among dBu, dBV, Vave, Vrms, and Vp-p and are displayed numerically. Readouts are displayed numerically, as well as with bar graphs for the VU and dB meters, and include peak indicators. In the Frequency Counter, both inputs are read and displayed independently. The frequency counter requires a fairly clean repeated waveform (such as a sine wave), and if the frequency cannot be determined, the figure “—” is shown. The range is 16 to 50k Hz; +4dBu and -10dB modes are available. The meters have very good resolution for fine adjustments.

The Signal-to-Noise function allows you to test the S/N ratio for any line-level device. This is a simple subtractive measurement and operates at +4 dBu or -10 dBV.

There are three Sweep functions: Frequency Response (amplitude) sweep, Impedance sweep (impedance of a load vs. frequency) and a programmable sine wave sweep. The Frequency Response function computes the gain of a device as a function of frequency. The Impedance sweep computes the impedance of a load as the signal generator is swept continuously from 20 to 20k Hz. The x-axis scale is variable from 20 to 20k ohms. Both the Frequency Response and Impedance sweep functions can operate in 1/3- or 1/12-octave mode, and the function averages the results over the selected 1/3- or 1/12-octave band. Results are displayed graphically on the LCD. Start and end frequency points (1/3-octave), as well as duration, may be set for the programmable sweep. There are 40 nonvolatile memories available in this mode.

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Reprinted with permission from Mix Magazine, July, 2000
© 2000, Intertec Publishing, A Primedia Company All Rights Reserved