Company Address: 1185 Chess Dr., Foster City, Cal. 94404.
In recent years, combination equalizer/RTAs have become quite popular, and these units do work very well in most cases. However, there are a number of excellent equalizers, both octave-band and parametric, which do not include any form of spectral display. Audiophiles should always have faith in their own listening tests, but it is difficult to make equalizer adjustments without an RTA for basic reference and guidance.
Not many octave-band RTAs are on the market, and the AudioSource sys tem which I checked out is one of the few made to fit within a typical audiophile's budget. The retail prices are $249.95 for the RTA-One analyzer, $54.95 for the accessory PNG-One pink-noise generator, and $29.95 for the RTA-One remote microphone. The RTA, noise generator, and an a.c. adaptor for the RTA ($15.95) were contained in a handy carrying case ($34.95). My first impression was that the RTA-One is slightly large and heavy for easy hand-holding. On the other hand (no pun intended), I appreciated the ruggedness of its steel case, a major contributor to the weight.
Three rotary switches on the front control "Power/Decay" ("Off/On Fast/ On Slow"), "Input Display" ("Line Lev el/Line RTA/Mic RTA/Mic Level"), and "Level (dB)." The level settings for "Mic S.P.L." range from "60" to "110" in 10-dB steps and for "Line" go from "-40" to "+ 10," also in 10-dB steps.
The knobs are of good diameter and have very legible indices. However, they were a bit hard to turn, despite the grooving on their edges, because their detents were quite stiff and they do not normally project very far from the pan el. Although the manual does not mention it, the knobs can be pulled out one-half inch, but I found that they were hard to pull.
All front-panel designations are white on a black background, making them easy to read.
The LED-type display above the knobs has the 10 standard octave spaced bands at 31.5, 63, 125, 250 and 500 Hz, and 1, 2, 4, 8 and 16 kHz.
The nine vertical LEDs for each band range from "- 10" to "+ 10" in 2.5-dB steps. All of these LEDs are red, with the exception of the 10 in the "0" row, which are green. The 2.5-dB steps are somewhat coarse, but a worthwhile improvement in resolution can be gained by adjusting level and EQ for equal momentary flashing in each channel when using pink noise. I really liked the green reference-level LEDs-1 felt that they helped to speed the equalization process.
At the top of the level display are three red indicators: "Power," "Low Bat." and "Overload." All are aids to proper operation of the RTA-One.
The microphone, which projects out from the end of the case, has a fairly large conical surround. The shape should help to prevent unwanted re flections, but the microphone cannot be checked with a standard calibrator--a common characteristic of most inexpensive RTAs. When the unit is in "Line RTA" and "Mic RTA" modes, the individual levels in each of the 10 bands are displayed. In the "Level" modes, the total energy in all 10 bands is summed and shown as a horizontal row of LEDs. A fast check showed that the RTA-One did quite an accurate job of summing, which most RTAs do not.
The AudioSource unit has good-quality jacks for external d.c. (standard coaxial), external microphone (phone), and line input (dual phono). The left/ right summing at the phono jacks was both unexpected and very nice to see included. On the back are four rubber feet for horizontal placement, and two rubber-strip feet are on the end for setting the unit vertically-handy for monitoring levels at a distance. The tripod socket on the back is useful when notes need to be taken and some form of holding is required. The battery compartment, which holds four AA cells, is easily opened with a quarter-turn of the slotted thumbscrew.
Before trying to do any equalizing, I checked over the ranges of levels available. Usually it is necessary to have at least 60 dB SPL in a room when making adjustments; the RTA One will indicate as low as 50 dB SPL ("- 10" on the "60" scale). It will show levels as high as 120 dB SPL (" + 10" on the "110" scale). A fast comparison showed that the SPL indications were accurate within about 2 dB. The reference level for line inputs is 1.0 V, so the range of voltage indications is from 3 mV ("-10" on the "- 40" scale) to 10 V ("1- 10" on the "+ 10" scale). With the signal levels in typical equipment ranging from perhaps 20 mV to 2 V, it appeared that line levels would not be a problem.
The owner's manual is not detailed, but the instructions are generally quite good, with important cautions on avoiding excessive boosts at the frequency extremes. I noticed a couple of oddities, including a reference to the "audible audio range." I monitored music for a while and concluded, as I had expected, that "Fast" mode was essential to get an accurate sense of the changing music spectra. To me, the attack time was good, but the decay time was a little fast. The 20-dB range was rather limiting for this use with many types of music. There seemed to be good separation between bands, and a vocal tone at the center of the 250-Hz band was indicated as 7.5 dB lower in the two adjacent bands-typical for many octave-band RTAs.
In preparation for doing some equalizing, I took a look at the PNG-One pink-noise generator. There were a number of similarities with the RTA One: Steel case, readily accessible battery compartment (dual 9-V), dual phono jacks, rubber feet, and a power-on indicator-a good collection of features. The PNG-One also has an out put-level control, important for setting test levels correctly. The sound from the device was quite smooth, with just a slight burbling, but no recycling clunk was observed.
With the PNG-One connected directly to the RTA-One, the display was quite flat, in general, but the level in the 31.5-Hz band was about 2.5 dB low.
The 63-Hz band was slightly low and the 500-Hz band slightly high. The response was almost exactly the same for both slow and fast response times.
You can use the PNG-One and RTA One to check for flat response in any piece of gear inserted between them; the display after insertion should be the same as before.
With pink noise fed through the en tire system, I checked the RTA-One microphone for directionality by pointing the unit directly at the loudspeaker and rotating it back and forth. Very little change occurred in the level of the 16-kHz band, showing that the micro phone was insensitive to exact pointing-a desirable trait which is lacking in most RTA microphones. The overall mike response was acceptably flat.
I found the AudioSource unit easy to use in a home listening system, and the green reference row helped to speed the process of equalizing and adjusting levels as needed. "Slow" had just a little bit of level spreading, and "Fast" was too jittery for most equalizing, as would be expected. I did find, however, that "Fast" was good for pinpointing the relative band levels-increasing the resolution of the level readout, as it were.
I also used the unit in a high-school auditorium, in a sound system used for a production with many musical numbers and a few skits. My 1/3-octave RTA wasn't fit to travel at the time, so the RTA-One and PNG-One were used to guide equalizing, to get basic smoothing for the system output and to compensate for some room conditions. AudioSource does not claim that this equipment can do sophisticated analysis, but they're right that it can be helpful in sound reinforcement.
I just lifted the RTA-One off my desk, and it still seems on the heavy side, but it also appears to be rugged and reliable, and I'll opt for those two characteristics any day in the week. Overall, there are quite a few more positive points than negative ones for this unit and its accessories. If you need an RTA, take a look.
-Howard A. Roberson
[adapted from AUDIO magazine/Dec. 1986]
Also see:
dbx 10/20 Computerized Equalizer/Analyzer (Jan. 1985)
ADC Sound Shaper SA-1 Real Time Analyzer (Sept. 1982)
Audio Control Richter Scale Bass EQ and Crossover (Aug. 1983)