The ATS-2 is a newly designed audio measuring instrument recently introduced by Audio Precision. Different from their other portable instruments, the Portable One and the ATS-1, the new ATS-2 (starts at $10,000) is controlled from a separate computer like the larger and more comprehensive System One and System Two. Like its larger System One and Two big brothers, the ATS-2 can be run from a desktop PC via either an ISA or PCI interface card or a PCMCIA card with a laptop PC.
Product PointsApplications: Test and measurement
Key Features: Rackmounted I/O/processor box; software with numerous test, measurement and analysis programs; computer-controlled via PCI, ISA or PCMCIA card
Price: starts at $10,000
Contact: Audio Precision at 800-231-7350, Web Site
The size of the ATS-2 is considerably smaller than Systems One and Two, making it an ideal candidate for portable use when allied with a laptop computer. Of interest, the ATS-2 has many of the digital analysis capabilities of the System Two at a considerably more affordable price. Some key features of the ATS-2 are analog and digital inputs and outputs, generation of test signals for both analog and digital devices, multifunctional audio analysis, spectrum analysis, multitone analysis and detailed harmonic analysis. An optional performance package adds digital interface analysis and increases the normal measurement bandwidth from 30 kHz to 120 kHz.
Signal inputs and outputs occupy the whole front panel width of the ATS-2. Two pairs of XLR connectors for input and output are employed for the digital connections to accommodate the dual connector mode. A single BNC for digital input and output are used for unbalanced digital connections. Analog inputs and outputs include XLR connectors for balanced and BNC connectors for unbalanced connections. Various monitor, sync and trigger BNC connectors, along with auxiliary control and PC interconnect cable D-sub connectors, a headphone jack and the AC power cord connector, are located on the rear panel.
The internal architecture of the ATS-2 is different from the System One and Two as there are no analog generators or analyzers present. Analog signals are digitally generated and converted to analog by D/A converters. In a like fashion, A/D converters digitize analog inputs and selected analog analyzer functions are accomplished digitally by DSP. The ATS-2 has two independent signal generators, one for analog output and one for digital output. These two generators can each create a large number of test signals including sine waves (as mono, stereo, phase-shifted), tone bursts, noise, square waves, special waveforms including polarity, special digital waveforms, and arbitrary waveforms including multitone signals (predefined or user defined using supplied utility). Analyzer functions include audio analyzer, spectrum analyzer, multitone analyzer, harmonic analyzer and the digital interface analyzer, if the performance option is installed.
The two-channel audio analyzer measures level, frequency, noise, THD+N, crosstalk, phase and frequency-selective level. Measurement functions offer combinations of detector selections and filtering including band limiting, band pass, weighting and notch. Detectors may be RMS, average and peak responding.
Offering a display that can be toggled between spectrum (frequency) and oscilloscope (time) views, the spectrum analyzer is a general-purpose FFT instrument that generates frequency-domain displays with selectable acquisition times, windowing and averaging functions.
Specially designed multitone stimulus signals are used with the multitone analyzer with specialized FFT analysis to rapidly capture a complete suite of audio performance parameters in less than one second.
If the performance option is installed, the interface analysis provides information about signal jitter, including amplitude, waveform and spectrum. The eye pattern display is an easily interpreted measure of digital interface behavior. Analytical and statistic analysis allows viewing of interface amplitude, pulse width, bit width and jitter histograms.
The harmonic analyzer provides a detailed look at individual harmonic distortion products as a function of frequency or amplitude.
I requested the PCMCIA option for the computer interface card to enable use of my Sony PCG-F420 laptop as the host computer. Installation went without a hitch. One interesting feature of the signal generators in the ATS-2 is their ability to put different signals in the two generator outputs. This is suggested in the two black arrow paths to the right of the frequency panel near the top of both the analog and digital generators. Three choices give either a variable phase in B-out relative to A-out, separate selectable frequencies for A-out and B-out, and separate selectable frequencies for A-out and B-out with the two frequencies added in both outputs.
I had occasion to use the variable phase in a prototype of Jim Bongiorno’s experimental Trinaural Processor (a stereo two-channel [L-R] processor that also synthesizes a center channel [L-C-R]). In this test, I put the A-out of the ATS-2 into the left input and the variable phase B-out into the right input of the converter and measured the left, center and right outputs as a function of this variable phase over a -180 to +180 degree range. The results are displayed in Figure 1. The left and right outputs were the same and are overlaid and the center output nulled out at plus and minus 180 degrees. In listening to this device, I suspected that the center channel output was out of phase with the left and right outputs. Using the wonderfully useful polarity test waveform, I verified this as shown in Figure 2. In this plot, due to the inversion in the system preamplifier feeding the device under test, the left and right outputs show the inversion and the center channel should have done so too but, as can be seen, does not.
I had occasion to check out a custom Class A power amplifier with the ATS-2. I set up a load resistor and did the test right at my office desk where I had the ATS-2 set up. A plot of distortion vs. power output into 8-ohm loads at 1 kHz and 10 kHz is shown in Figure 3. Another test was to plot the spectrum of a 10W signal at a frequency of 1 kHz on a log frequency basis to show the AC line hum components and the distortion spectra of the test signal. This is plotted in Figure 4. Both of these tests are for both channels.
A D/A converter that I had been using for some time had to be returned to the manufacturer during the review period and I decided to make a test or two upon it with the ATS-2. In Figure 5, I used the harmonic analyzer function to measure the second and third harmonics at digital full scale as a function of frequency. The converter was fed with the digital output of the ATS-2 at a 48 kHz sampling frequency and the resultant analysis using the harmonic analyzer was set for receiving the converter’s analog output. In another test on this converter, I fed a full-scale S/PDIF 1 kHz audio signal into it and used the jitter generator function to add 50 mUI (about 8.14 ns peak) of a 500 Hz sine wave jitter signal. The resultant analog output spectrum with and without the added jitter is plotted in Figure 6. As can be seen, the jitter increased the noise floor and added sum and difference frequencies of 500 Hz, 1,500 Hz and 2,500 Hz to the output spectrum as a result.
One consequence of the design that I do miss is the ability to measure a spectrum of the distortion residue of a device – one has to accept the presence of the fundamental in the display. This is because the analyzer can be either a THD+N device or a spectrum analyzer, but not both at the same time. However, one can monitor the distortion residue on the back panel monitor output. The dynamic range of the instrument is good enough, though, to usefully measure very low amounts of distortion in the presence of the fundamental.
Audio Precision has created a versatile and portable instrument that will answer the needs of many different kinds of testing functions at an attractive (compared to the System Two) price.