Describes using LabVIEW with APx in a lab or automated production environment. Examples using the APx LabVIEW virtual instrument driver are shown.
A look at some of the important features needed in an acoustic audio analyzer, the problems you may encounter in non-ideal testing environment, the needs of good production line testing, and the range of measurements and results that should be produced.
Cost benefit analysis of high performance, low price audio test equipment in production.
Explains the various ways to view, measure, and manipulate digital metadata, primarily over the HDMI interface.
Serial digital signal analysis is essential in research and development for evaluating audio circuit designs at the chip and at the board level. This AP Applied reviews serial testing procedures, and describes the abilities of the DSIO for APx, as well as the PSIA-2722 for the 2700 Series.
A look at the traditional ways of examining out of band noise signals, as well as the advantages of using an ultra-high bandwidth audio analyzer with full 24 bit FFT resolution from DC to beyond 1 MHz.
In collaboration with Dolby engineers, Audio Precision has developed APx-based test solutions, available to Dolby licensees, to support both the Dolby Digital Plus™ Consumer Decoder SDK and the MS11 Multistream Decoder SDK. In the case of Dolby Digital Plus, compliance testing includes well over 1,200 individual measurements which, if performed manually, could easily take over a week. The APx solution reduces that time to hours. More importantly, because APx generates the test sequence with all appropriate limits, there is no time wasted on recreating a test methodology or deciphering test requirements. Since Dolby MS11 also supports Dolby Digital Plus, this application note primarily focuses on the MS11 SDK test solution.
TECHNOTE 101 describes the basic principles and techniques needed to operate System Two / 2700 Series instruments using the Audio Precision control software as an Active X automation server within the LabVIEW environment. Although it is possible for LabVIEW to directly control GPIB versions of Audio Precision instruments, GPIB control of Audio Precision systems is not the subject of this TECHNOTE. Instead, TECHNOTE 101 deals with the capability of LabVIEW to control the standard APIB versions of Audio Precision PC-controlled instruments via the instrument control software, using Microsoft ActiveX automation.
The AP High Speed Tester (HST) application was originally developed to test playback only devices on the production line. The objective was a fast, accurate and easy-to-operate test station with a limited graphical user interface that just indicated the test results and had the ability to save results to a log file.
In addition testing play-back devices, HST 2.0 can use the instrument's generator to drive the input of the device under test. Both input and output can be set to digital or analog, and limits, user prompts and sample rate can be defined easily via a new setup utility.
This flexibility allows HST 2.0 to test almost any type of audio device - amplifiers, DACs, ADCs, signal processors, MP3 / DVD players etc. - quickly and easily.
Technote 104 discusses methods of making a set of basic measurements using an Audio Precision 2700 Series or ATS-2 audio analyzer.These are Level Frequency Response THD+N Phase Crosstalk Signal-to-Noise Ratio
In this technote, we discuss how to test the analog sound quality of FM radio receivers using an Audio Precision APx500 Series audio analyzer. We also discuss how to test the Radio Data System (RDS), which allows text, such as song title and artist, to be transmitted digitally as part of the analog radio signal.
In this technote we describe and compare two different methods to measure PSRR. Then we give instructions for using the APx PSRR Measurement Utility, which simplifies the calculations and graphing on APx analyzers.
This technote is included in the APx PSRR Measurement Utility download.
Describes how to measure the sound pressure level developed by portable audio players and their associated headphones, according to British Standard / European Norm 50332. Also shown is how to use the APx Portable Audio Player / Portable Headphone Test Utility to facilitate making the necessary measurements with an APx500 analyzer.
Performing the described tests requires that you download the APx Portable Audio Player / Headphone Test Utility. This Technote is also included in that download.
This Technote discusses the techniques necessary to perform the “Basic Six” audio measurements on consumer-level PC audio devices. This category includes sound systems integrated into notebooks, netbooks, tablets, and PC motherboards, as well as expansion cards and some external devices. It doesn’t include USB-connected headsets, nor pro-audio devices with balanced input and output connections.
Includes APx project and .wav test signal files for playback
Addresses conversion of tests and procedures/macros written using AP’s Windows based APWin, AP2700, or ATS software to APx500. If you are using AP’s DOS based S1.EXE software for System One, please refer to Technote 109 instead.
This Technote discusses techniques for testing the audio performance of USB headsets using an Audio Precision APx analyzer. Includes APx projects and wave files.
Acoustic sounds or noise in the environment is typically measured with a handheld sound level meter. This Technote explains some of the theory behind such measurements, and how to make them instead using an APx analyzer. Using the analyzer adds the capability to perform spectrum analysis, and to visualize the character of the sound signal over time. The latter is especially valuable when measuring non-steady state sounds, such as a pulsating alarm. Requires the APx Sound Level Meter Utility, available as a separate download, to make the measurements.
Describes how to test microphone preamplifier phantom power, with and without simultaneous audio. You may instead download the "APx Phantom Power Measurement Project," which runs the tests (that download also includes this Technote).
Making noise measurements of microphone preamplifiers (and other high-gain circuits) involves special techniques that differ from those used to measure low-gain devices. This technote explains the theory as well as how to make these measurements.
Smartphones and tablets provide many ways to route audio. This technote shows you how to make connections and test the sound quality for a variety of these signal paths. Where possible, we will use file-based test signals and recordings to measure the quality of signal paths so that we are not measuring the impairments of multiple paths simultaneously.
This Technote has a short review of how PDM works, describe relevant audio tests, looks at the APx PCM module, and conclude with hands-on testing of a PDM MEMS microphone and a PDM microphone input.
Technote 121 describes the PESQ and POLQA Perceptual Audio test models, how they are implemented in APx, and when each is appropriate to use. Brief contextual comparison to STI (Speech Transmission Index) is also provided. Please also see the Technote 121 supplemental file, which includes additional POLQA and PESQ information provided by Opticomm GmbH.
The A2DP Bluetooth® profile is used for high quality music transmission, employing a variety of supported codecs that include MPEG-1, MPEG-2, MPEG-4, AAC, ATRAC, aptX and aptX Low Latency. This technote illustrates how the APx Bluetooth option is used to control and monitor codec selection, measure latency, and test all essential audio parameters such as frequency response and THD+N for Bluetooth-enabled music playback devices.
Enabling high-channel count, high-quality audio transport via Ethernet, the Dante protocol is being designed into a growing number of pro-audio products and systems. However, testing Dante-enabled devices can present some unique challenges. Our latest technote delves into this application and walks through two example test scenarios using APx500 Series audio analyzers.
This Technote is intended for those involved in design and test of devices with Pulse Density Modulation (PDM) interfaces. It requires an Audio Precision APx analyzer with the APX-PDM option module (model 228), APX-AMC Advanced Master Clock, and APx500 software version 4.2 or later.
This TechNote discusses STI measurement, including the different methods identified in IEC 60268-16, a brief comparison of STI versus PESQ and/or POLQA perceptual audio testing, and finally a full discussion of STIPA method-based measurements using an APx500 Series audio analyzer and Audio Precision's STI measurement plug-in.
This Technote examines the automated test capabilities built into the APx500 measurement software, with emphasis on features recently added in release v4.2 to support production test of electro-acoustic devices. TN129 also provides a practical example, specifically the configuration of APx for production test of loudspeakers, and includes discussion of "golden units" (reference devices), input equalization, multiple sequences in a single project, and Production Test mode.
This Technote describes how to setup communication between AP Basic and GPIB instrumentation (using the National Instruments GPIB Interface.)
This utility determines the signal polarity between the Analog Generator Outputs and the Analog Analyzer Inputs. A common error in manufacturing of loudspeaker systems is to connect voice coils with reversed polarity. Even when all drivers in a multi-way system are phased correctly with respect to one another, it is possible to have the interior wiring to the external connection terminals of the cabinet reversed. An individual driver reversed will cause a dip in frequency response near the crossover frequency to the adjacent driver, since the two speakers are then producing acoustical output of nearly identical amplitudes but out of phase. An entire system wired out-of-phase would presumably be undetectable in a monaural application, but unacceptable in stereo systems. With minor adjustments, this procedure can be run as a stand-alone test, or it can be incorporated into other test setups. The procedure can test a single path, or it can test stereo channels. Equipment required is DSP or Dual-Domain version of System One, System Two, or System Two Cascade, and a microphone if you are testing acoustic paths such as loudspeakers.
This Technote describes how to set up and use the dBr unit as dBSPL. Automated AP Basic macros (procedures) are available to facilitate the calibration. These macros apply to the instrument analog analyzers. Additionally, two computational methods are described to help you understand the macros, and to help you calibrate a measurement microphone without the macros.
Group delay is a property of a device or a system: a plot of the change in phase of the response as a function of frequency; it is the negative derivative (slope) of the phase-vs-frequency characteristic of a device. Constant group delay across the frequency band means that all portions of a wideband signal arrive simultaneously. A pure time delay, equal at all frequencies, gives a level straight-line plot of phase versus frequency. In an audio component, this plot may vary with frequency, and the component is said to produce group delay distortion. Group delay is of interest to audio engineers, particularly in the design and test of low-pass filters used in digital audio and in loudspeaker design areas. For instance, an anti-aliasing filter will typically have a phase response curve which slopes sharply down at high frequencies. This means that the high-frequency components will be delayed longer in their passage through the filter, resulting in a loss of precision in musical transients and a more diffuse stereo image. It is possible to correct the group delay distortion of such filters by using an all-pass network, but this is seldom done in practice.
Document describes in detail the features and operation of the APx PDM module. The module is an available option for the APx555, APx52x Series and APx58x Series Audio Analyzers.
This book by the late Julian Dunn examines in great detail techniques for evaluating the performance of converters and digital interfaces.
Includes a full set of AP2700 macros and tests that accompany the text.
Discusses writing and reading good audio specifications. Guidelines are provided, then key specifications for two classes of audio device are examined for correct expression and form, with examples of real-world specs for comparison.
Audio analyzers are optimized to make high quality measurements up through their maximum specified bandwidths. The presence of significant energy above these bandwidths can have a profound effect on the audio measurements and possibly induce errors. This white paper provides valuable information on avoiding the possibility of errors when testing digital to analog converters and other audio devices that contain significant energy above the audio band. Written by Bruce Hofer
Switch-mode audio power amplifiers are becoming increasingly popular due to their smaller size, lower weight, and improved efficiency. Their advantages are obvious in low power battery operated personal audio players and laptop computers. However they are also progressively displacing more traditional linear designs in mainstream applications such as home entertainment systems, automotive sound systems, and professional installations where high quality audio is important. Measuring the performance of switch-mode amplifiers presents some new and unique challenges. They inherently generate ultra-sonic artifacts and spurious signals with slew rates that can provoke non-linear behavior within the input stages of high quality audio test and measurement equipment. Absolutely worthless and inaccurate results can result unless effective measures are taken to prevent this non-linear behavior. Written by Bruce Hofer.
This reference handbook is a practical, hands-on guide for workers in all phases of the audio field. It covers basic tools and techniques, common environments for audio testing, application of these techniques to common audio devices, the typical ranges of performance to expect in different devices, and a glossary of terms and key specifications used in audio measurement. 178 pages Written by Bob Metzler.