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Audio Precision Technical Content


Technotes and AP Applied (29) Whitepapers, Articles, and Books (6)

Technotes and AP Applied

AP Applied: APx Automation with LabVIEW v1

Describes using LabVIEW with APx in a lab or automated production environment. Examples using the APx LabVIEW virtual instrument driver are shown.


AP Applied: Acoustic Response v0

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.


AP Applied: Calculating ROI of Audio Test in Production v1

Cost benefit analysis of high performance, low price audio test equipment in production.


AP Applied: Digital Protocol Analysis

Explains the various ways to view, measure, and manipulate digital metadata, primarily over the HDMI interface.


AP Applied: Dolby and dts Compliance Testing v2

Every device that bears a Dolby or dts logo is required to go through a compliance test process to insure that it meets the respective technical requirements. This AP Applied describes compliance testing using the APx585 with HDMI, utilizing features such as self-generated encoded test signals (closed loop testing), report generation, automation, and more. Testing examples are shown for an HD receiver and a disc player.


AP Applied: Serial Digital Measurements with APx v1

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.


AP Applied: Ultra-High Bandwidth Analysis v0

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.

Available translations


Technote 101: LabVIEW ActiveX Automation for Audio Precision Instruments v1 (View previous versions)

TECHNOTE 101 describes the basic principles and techniques needed to operate Audio Precision instruments using the instrument's Audio Precision control software as an Active X automation server within the LabVIEW environment. LabVIEW is a graphical programming development environment from National Instruments Corporation (NI). Engineers, scientist and technicians create virtual instruments (called VI in LabVIEW) to control and automate a wide variety of test and measurement instruments and to gather and manipulate the resultant test data. 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.


Technote 102: Using Audio Precision High Speed Tester (HST) v2.01

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.

Available translations


Technote 104: Introduction to the Six Basic Audio Measurements

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

Available translations


Technote 105: FM Radio Receiver Testing with APx Audio Analyzers v0

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.


Technote 106: Measuring PSRR (Power Supply Rejection Ratio) v0

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.


Technote 107: Measuring the Sound Pressure Level of Portable Audio Player Headphones v1

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 tests described in this Technote requires that you download the APx Portable Audio Player / Headphone Test Utility, which includes the Windows installer, VB.NET source code, and this Technote.


Technote 108: PC Audio Testing v0

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


Technote 110: Legacy Instrument Migration to APx v0

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.


Technote 111: Testing USB Headsets v1

This Technote discusses techniques for testing the audio performance of USB headsets using an Audio Precision APx analyzer. Includes APx projects and wave files.


Technote 113: Measuring Sound Pressure Level with APx v1.1

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.


Technote 114: Measuring Phantom Power v1

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).


Technote 115: Measuring Microphone Preamplifier Noise

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.


Technote 116: Testing Smartphones and Tablets v1

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.

Includes the accompanying APx project file. The associated APx Smartphone and Tablet Video Test Files and APx Smartphone and Tablet Audio Test Files may be downloaded separately.


Technote 117: Measuring PDM Microphones and Inputs with APx v2

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 118: Measuring Jitter with J-Test


Technote 120: Smartphone Audio Test App for Android

This technote describes how to install the necessary software on the smartphone or tablet device under test (DUT), how to use the Smartphone app on the DUT, and which APx projects to use for testing the various signal paths. Package containing: 1) The APx Smartphone Audio Test app for smartphones and tablets running the Android OS version 4.0 or higher. 2) Associated APx project files 3) Technote TN120: Using the APx Smartphone Audio Test App.


Technote 121: Perceptual Audio Testing v1.1

Technote 121 describes the PESQ and POLQA Perceptual Audio test models, how they are implemented in APx, and when each is appropriate to use.


Technote 123: Measuring Bluetooth A2DP Codecs v1.0

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.


Technote 15: GPIB Communication from AP Basic

This Technote describes how to setup communication between AP Basic and GPIB instrumentation (using the National Instruments GPIB Interface.)


Technote 27: Polarity Test Procedure

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.


Technote 28: Measurement Microphone dBSPL Calibration

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.


Technote 29: Computing Group Delay from Phase Data Using APWIN

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.


Whitepapers, Articles, and Books

APx PDM Option Technical Details v2 (View previous versions)

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.


Appnote 5: Measurement Techniques for Digital Audio (Julian Dunn) v2

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.


How to Write (and Read) Audio Specifications

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.


Limitations in making audio bandwidth measurements in the presence of out of band noise

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


Measuring Switch-mode Power Amplifiers

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.

Available translations


The Audio Measurement Handbook v1

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.

Available translations


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