Technotes & Appnotes
Each Audio Precision Technote and Appnote is a focused look at a single topic in audio test and measurement—sometimes a particular solution, perhaps a time-saving tip or an in-depth exploration of a difficult concept. Many of the Notes are specific to Audio Precision analyzers, and some to a particular instrument. However, the approaches and strategies taken in a certain testing environment are often transferable to another situation, and our customers find value even in the older Notes written for legacy instruments.
For earlier Technotes relating to legacy software and applications, visit Legacy Technotes
If there is a subject you feel would be appropriate for a Note, please contact us with your idea.
Technotes
| Technote 104: Introduction to the Six Basic Audio Measurements By David Mathew |
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Technote 104 discusses methods of making a set of basic
measurements using an Audio Precision 2700 Series or
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| Technote 103: Dolby Digital DVD Certification Tests By Bill Rich and David Mathew |
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| This Technote describes the use of a group of over 30 AP Basic macros that make Dolby Digital DVD testing quick and easy, using an Audio Precision analyzer system and input switcher. Both real-time Dolby Digital encoding (with Audio Precision's OPT-2711 Dolby Digital option) and DVD-Playback methods are supported. The macros and measurement results were designed to correspond to the organization of Dolby's DVD test results documents to help you gather most of the technical information you'll need for Dolby Digital DVD certification. Notes
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v2.01 corrects DC measurement bug associated with AP2700. ATS-2 was not affected Technote 102: Using Audio Precision HST by Bill Rich, Daniel Knighten and Dave Mathew |
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| 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 2.01 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. Notes
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Technote 101: |
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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. |
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Technote 29: |
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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. |
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| Technote 28: Measurement Microphone dBspl Calibration |
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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. |
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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. |
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Technote 21: |
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The Audio Precision System Two's dual channel FFT signal analysis provides an alternate method of obtaining frequency response measurements. With power spectrum averaging of the FFT, the test signal can be regular audio program material. This ability to use music as the test signal can be useful in situations where conventional test signals would be annoying to listeners, such as in broadcasting or live performances. The only requirement for the source program is that it have sufficient energy, over time, at all frequencies in the bandwidth of interest. In other words a rock band or a symphonic orchestra would be a better choice than a single folk singer with a guitar. |
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Technote 19: |
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You can easily create an HTML-based help system to guide production technicians through APWIN Basic procedures. HTML, or HyperText Markup Language, is the language used by web browsers to format and display web documents. HTML-based help system files can be viewed by anyone with Internet or Intranet access, or they can be local files on a single computer. They can be updated at one location and can grow as your procedures grow. You can save files as HTML from word processors such as Microsoft Word 97, or you can use web development tools such as Dreamweaver or Front Page to create more sophisticated web-based help documents. It is possible to design robust interactive web-based help systems, including such features as displaying animated demonstrations, capturing and distributing information, using a database, and providing web-based training with audio, video, animations, etc. |
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| Appnote 6: Digital Audio Broadcast Receiver Audio Testing |
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The objective of this application note is to describe accurate, timesaving techniques for testing the audio quality of Digital Audio Broadcast (DAB) receivers with Audio Precision 2700 series and ATS-2 audio analyzers. While the information in this document focuses on DAB as it applies to satellite radio transmissions and reception, and more specifically to appropriate receiver testing techniques, there is also useful information contained here applicable to the larger universe of DAB technology. The problem most frequently encountered in the audio testing of DAB receivers relates to signal mute intervals (dropouts) caused by the receiver when stimulated with a synthesized radio signal from a radio frequency (RF) generator. In order to avoid unreliable measurements during these dropouts, it is critical that audio tests be performed in synchronization with your RF generator. |
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Appnote 5: |
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Much has been written about digital audio, its defining standards, the ever-changing hardware and software, the various applications in recording and broadcasting and telecommunications and the audibility of this or that configuration or artifact. In this book the late Julian Dunn focused instead on the measurement of digital audio signals, and examined in great detail techniques to evaluate the performance of the converters and interface through which the audio passes. Mr. Dunn passed away early in 2003, cutting much too short a brilliant career as one of the world's premier designers and consultants in digital audio. Note: You can also order this Appnote in printed book form. Contact your local Sales Partner |
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Appnote 1: |
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This expansion and revision of the original Audio Precision Compact Disc Player Testing Application Note (AN-1) includes many new test techniques as well as refinements and improvements on the original tests. Test and procedure files supplied with this application note provide new convenience and ease-of-use for testing CD players using these instruments. Files created for both System One and System Two using APWIN are available. All audio tests are described with an explanation of the critical settings for each test and discussion of interpreting the test results. New test procedures using the powerful APWIN Basic procedure language streamline and automate test selection, setup and operation. For a fast start select File, Open Procedure CDTEST and Procedure, Run from the toolbar at the top of APWIN. The common audio tests: frequency response, distortion and noise (THD+N), signal-to-noise ratio, crosstalk and interchannel phase - are all available. Also included are specialized and difficult tests such as distortion at low amplitudes, decoder linearity measured to below the Least Significant Bit, quantization noise, dynamic range, SMPTE and twin-tone (CCIF) intermodulation distortion and Wow and Flutter as an impulse noise test. All are explained in detail. |
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