A111D2 Mfl7Dba STANDAROS& TECH R...C. NATL .NST OF A1 11 02487062 .-k»- ''Oa o NBS TECHNICAL NOTE 1219 \ *<"fEAU 0* * U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards Electrical Performance Tests for Audio Distortion Analyzers O.B. Laug, G.N. Stenbakken, and T.F. Leedy QC 100 .U5753 No. 1219 1986 C 2 . m he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The jP Bureau's overall goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit . To this end, the Bureau conducts research and provides: (1) a basis for the nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is performed by the National Measurement Laboratory, the National Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering The National Measurement Laboratory Provides the national system of physical and chemical measurement; • Basic Standards^ coordinates the system with measurement systems of other nations and • Radiation Research furnishes essential services leading to accurate and uniform physical and • Chemical Physics chemical measurement throughout the Nation's scientific community, in- • Analytical Chemistry dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops, produces, and distributes Standard Reference Materials; and provides calibration services. 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The In- stitute consists of the following centers: The Institute for Materials Science and Engineering Conducts research and provides measurements, data, standards, reference • Ceramics materials, quantitative understanding and other technical information funda- • Fracture and Deformation ^ mental to the processing, structure, properties and performance of materials; • Polymers addresses the scientific basis for new advanced materials technologies; plans • Metallurgy research around cross-country scientific themes such as nondestructive • Reactor Radiation evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evalua- tion; and broadly disseminates generic technical information resulting from its programs. The Institute consists of the following Divisions: 'Headquariers and l.aboraiories ai Gaiihersburg, MD, unless otherwise noted; mailing address Gaiihersburg, ,MD 20899. ^Somc divisions within the center arc located at Boulder, CO 80303. '[.(Kaied at lioulder, CO, with some elements at Gaiihersburg, MD. NBS BESEAECH mPOTMATION CENTER pi /\/<^5 lechfJicAl ore- qc » « » 100 Electrical Performance Tests for '^^^ Audio Distortion Analyzers '- O.B. Laug, G.N. Stenbakken, and T.F. Leedy Electrosystems Division Center for Electronics and Electrical Engineering National Engineering Laboratory National Bureau of Standards Gaithersburg, MD 20899 Issued January 1986 Prepared for: U.S. Army Communications Electronics Command Fort Monmouth, New Jersey 07703 / \'^ \ Q U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige. Secretary NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director National Bureau of Standards Technical Note 1219 Natl. Bur. Stand. (U.S.), Tech. Note 1219, 156 pages (Jan. 1986) CODEN: NBTNAE U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1986 For sale by the Superintendent of Documents. U.S. Government Printing Office, Washington, DC 20402 TABLE OF CONTENTS Page List of Figures iv List of Tables v Abstract 1 1. Introduction 1 2. Background 2 3. Audio Distortion Analyzer Applications & Principles 3 4. Distortion Analyzer Performance Measurements 9 4.1 Input/Output Characteristics 10 4.1.1 Input Impedance 10 4.1.2 Input Common-Mode Rejection Ratio (CMRR) 14 4.1.3 Input Protection 19 4.1.4 Monitor Output Impedance 19 4.1.5 Monitor Output Frequency Response 22 4.1.6 Monitor Output Linearity (Absence of Clipping) 23 4.2 Voltmeter Mode 23 4.2.1 Voltmeter Accuracy and Range 23 4.2.2 Bandwidth 24 4.3 Distortion Measurements 25 4.3.1 Two Sine Wave Test 26 4.3.2 3:1 Crest Factor Signal Test 30 4.3.3 SINAD Test 40 4.3.4 Residual Distortion and Noise 42 4.4 Filter Characteristics 45 4.4.1 High Pass/Low Pass Filter Measurements 45 5. References 49 Appendix A A-1 Appendix B B-1 Appendix C C-1 Appendix D D-1 Appendix E E-1 Appendix F F-1 111 List of Figures Page Figure 1 Block diagram of a harmonic distortion measurement. The basic distortion analyzer has a tunable notch filter to remove the fundamental frequency component of the signal and a detector to measure the remaining signal 5 Figure 2 Block diagram of the essential elements contained in a modern audio distortion analyzer. 8 Figure 3 Equivalent circuit for determing input impedance 11 Figure 4 Test setup for measuring the common-mode rejection ratio of an audio distortion analyzer (preferred method) 15 Figure 5 An alternate method of measuring the common-mode rejection ratio of an audio distortion analyzer 18 Figure 6 Equivalent circuits for determining output resistance 20 Figure 7 Test setup for measuring distortion accuracy with the sine wave signals 27 Figure 8 Test setup for measuring distortion accuracy with signals that have a 3:1 crest factor 29 Figure 9 Waveform of 3:1 crest factor signal using 9th harmonic pulses with amplitudes of 1.86 times the fundamental amplitude 34 Figure 10 Waveform of 3:1 crest factor signal using 19th harmonic pulses with amplitudes of 0.825 times the fundamental amplitude 35 Figure 11 Magnitude spectrum of 3:1 crest factor signal using 9th harmonic pulses 36 Figure 12 Magnitude spectrum of 3:1 crest factor signal using 19th harmonic pulses 37 Figure 13 Test setup for measuuring SINAD accuracy 39 Figure 14 Test setup for measuring residual distortion and noise. ... 41 Figure 15 Test setup for measuring residual distortion and noise at input levels above 10 volts rms 43 Figure 16 Test setup for measuring the quality of the low-distortion oscillator 44 Figure 17 Typical Bode plots of high and low-pass filters 46 iv List of Tables Page Table 1 Typical AC Calibration Accuracy Specification 24 Table 2 Magnitude for the 9th Harmonic Pulse 31 Table 3 Magnitude for the 19th Harmonic Pulse 32 Table 4 Crest Factors Resulting from Various Combinations of Amplitude and Harmonic Number 32 Table 5 Error Resulting From Using a Limited Number of Harmonics to Calculate THD 33 ELECTRICAL PERFORMANCE TESTS FOR AUDIO DISTORTION ANALYZERS 0. B. Laug, G. N. Stenbakken, and T. F. Leedy Abstract Electrical performance test procedures for audio distortion analyzers were developed by the National Bureau of Standards for the U. S. Army Communications-Electronics Command. The report provides detailed, step-by-step test procedures that are based on specifications supplied by the Army for purposes of evaluating audio distortion analyzer bid samples. Examples of data sheets and tables are also provided for recording interim and final results. This report discusses the philosophy of each measurement procedure with a view toward providing an understanding of the basic metrology required to perform the measurements. In addition, the sources of measurement error are discussed. The primary applications and basic principles of modern audio distortion analyzers are also presented. Key Words: audio distortion analyzer; distortion analyzer; distortion; distortion specification; and test procedures. 1. INTRODUCTION This report describes test procedures that were developed by the National Bureau of Standards (NBS) for the U. S. Army Communications-Electronics Command