|
An Audio Analyzer is a test and measurement instrument used to objectively quantify the audio performance of electronic and electro-acoustical devices. Audio quality metrics cover a wide variety of parameters, including level, gain, noise, harmonic and intermodulation distortion, frequency response, relative phase of signals, interchannel crosstalk, and more. In addition, many manufacturers have requirements for behavior and connectivity of audio devices that require specific tests and confirmations. Audio analysis requires that the device under test receive a stimulus signal of known characteristics, with which the output signal (response) may be compared by the analyzer in order to determine differences expressed in the specific measurements. This signal may be generated or controlled by the analyzer itself or may come from another source (e.g., a recording) as long as characteristics relative to the desired measurement are defined. As test and measurement equipment, audio analyzers are required to provide performance well beyond that of the typical devices under test (DUTs). High quality audio analyzers must demonstrate vanishingly low levels of noise, distortion and interference in order to be deemed trustworthy by engineers and designers. For example, while a commercial CD player can achieve a total harmonic distortion plus noise (THD+N) ratio of approximately -98 dB at 1 kHz, a high quality audio analyzer may exhibit THD+N as low as -121 dB (typical performance of the Audio Precision APx555). Audio Analyzers find use in both development and production of products. A design engineer will find it very useful when understanding and refining product performance, while a production engineer will wish to perform tests to rapidly confirm that units meet specifications. Very often audio analyzers are optimized for one of these two cases. Current popular audio analyzer models include: APx585 and APx555 (Audio Precision), dScope Series III (Prism Sound), U8903A (Agilent) and the UPP and UPV analyzers (Rohde & Schwarz). ==History== One of the earliest reliable sources used for audio test was the first product made by Hewlett-Packard in 1939, the HP200A audio oscillator. The clever and inexpensive design of the HP200A allowed testers to generate very high quality, low distortion sine waves that could be used for testing. This was followed by the company's introduction of the HP320A and HP320B Distortion Analyzers in 1941. These early analyzers could only determine total harmonic distortion and noise combined, and worked by employing a steep notch filter to remove the fundamental frequency of the stimulus signal from the output of the DUT. The remaining signal was measured as an AC voltage, and thus allowed for the manual calculation of total noise and distortion to approximately 0.1% minimum. Subsequent products from HP, Wandell & Goltermann, Radford, Marconi, Sound Technology, and Amber continued to refine measurement capabilities from the 1950s through the 1970s, but the model of usage remained relatively constant; signal generators and analyzers were separate pieces of equipment, and testing involved careful tuning of each one by a person with high technical skills. This changed in 1980 with the introduction of the Tektronix AA501 Distortion Analyzer, which automated the processes of setting levels, frequency tuning and nulling. At this same time Hewlett-Packard introduced the popular HP8903B, which combined a high quality signal generator and analyzer in a single unit. By the mid-eighties, Tektronix ceased production of audio test equipment, and in 1984 members of the team that had developed the AA501 started Audio Precision. The first Audio Precision product was the System One, which combined an integrated generator and analyzer with a connected PC to fully automate test procedures and provide a much higher degree of computational power than the simple microprocessors used in other products at the time. The novel use of a PC allowed for a high degree of custom automation and enabled a radically different visual presentation of results. The combination of PC technology with audio analyzers was adopted by others, including Prism Sound (dScope), Rohde and Schwarz (UPL), and Stanford Research (SR1). As the power of available PCs increased, measurements themselves migrated from being performed internally by audio analyzers to applications running on connected PCs performing FFT (Fast Fourier Transform) calculations, greatly increasing the flexibility and resolution of many results. In addition to analog, audio analyzers today are frequently capable of generating and measuring audio over several different types of digital I/O. For example, the Rohde and Schwarz UPP offers AES/EBU, S/PDIF, I²S and HDMI options; the Audio Precision APx500 Series analyzers support AES/EBU, S/PDIF, I²S, HDMI, PDM (Pulse Density Modulation), and Bluetooth radio, and are fully DSP based. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Audio analyzer」の詳細全文を読む スポンサード リンク
|