Audio-Precision音频分析仪测试介绍.ppt

AP Introduction&THD+NAnalyzer input and XLR connectorAP PanelAudio specificationsTHD+N1精选课件AP introductionAnalyzer input cable connectionAnalyzer input cable connection-Single ended output(MP3 headphone)-Single ended output(MP3 headphone)2 Signal,3 Ground.2 Signal,3 Ground.e.g.,Channel A:2 Left output,3 Ground e.g.,Channel A:2 Left output,3 Ground Channel B:2 Right output,3 Channel B:2 Right output,3 GroundGround-Differential output(loudspeaker)-Differential output(loudspeaker)2 Non-inverting signal,3 Inverting 2 Non-inverting signal,3 Inverting signalsignal2精选课件AP introductionXLR ConnectorXLR Connector3精选课件AP introductionXLR ConnectorXLR Connector-In reference to its original manufacturer,James H.Cannon,founder of Cannon Electric in Los Angeles,California(now part of ITT Corporation),the connector is colloquially known as a cannon plug or cannon connector.-The most common is the 3-pin XLR3,used almost universally as a balanced audio connector for high quality microphones and connections between equipment.-XLR plugs and sockets are used mostly in professional audio and video electronics cabling applications.Home audio and video electronics normally use RCA connectors.4精选课件AP introductionAP1 PanelAP1 Panel5精选课件AP introductionTHDTHD +N vs LevelN vs Level CurveCurve6精选课件AP introductionAnalyzer PanelAnalyzer Panel7精选课件AP introductionSweep DefinitionsSweep Definitions PanelPanel8精选课件AP introductionFrequency ResponseFrequency Response-Frequency Response measurements are made by stepping or sweeping a sine wave oscillator,at a fixed amplitude,across the spectrum of interest.-Usually stated in terms of dB variation from some reference midband frequency(e.g.,1KHz).-The test may be easily modified.The frequency range and direction of sweep can be changed from the 20 KHz 20 Hz stored by entering new values for START and STOP under SWEEP(F9)DEFINITIONS panel.9精选课件AP introductionSignal to Noise RatioSignal to Noise Ratio-Signal to noise ratio,as a relative measurement,must be made with reference to a specific output amplitude from the device under test.-The rated output amplitude must be calibrated as the 0 dBr reference of the analyzer.Then the residual output amplitude(noise)is measured and expressed in dB relative to the reference.10精选课件AP introductionCrosstalkCrosstalk-Signals from one channel leaking into another channel.Normally,this happens between left and right stereo channels.-A generator drives one channel and this channels output value is noted;meanwhile the other channel is set for zero volts.The measured channel left open.-Whatever signal is induced into the tested channel is measured at its output with an rms voltmeter and noted.A ratio is formed by dividing the unwanted signal by the above-noted output test value,and the answer expressed in dB.11精选课件AP introductionHarmonic Distortion ConceptsHarmonic Distortion Concepts-Harmonic distortion may be measured and expressed as total harmonic distortion(THD),or as total harmonic distortion plus noise(THD+N).-THD is the distortion that occurs on harmonics of the original signal.Noise is the more random,uncorrelated distortion.-In all cases,stimulus from a very pure sinewave generator is fed to the input of device under test.The generator must have significantly lower distortions than that of device.12精选课件AP introductionHarmonic Distortion ConceptsHarmonic Distortion Concepts-THD refers to measurement methods which individually measure the amplitude of each significant harmonic in a narrow bandwidth,then combines them in root-mean-square fashion to produce a single number.-THD+N,refers to the measurement technique in which the fundamental component is removed by a bandreject(norch)filter and all remaining energy measured,including harmonics and noise.13精选课件AP introductionHarmonic Distortion ConceptsHarmonic Distortion Concepts-Bandwidth and THD+NThe measured THD+N of a device will vary with the measurement bandwidth.You will almost always want to restrict the measurement bandwidth using high-pass and low-pass filters,and you must include the bandwidth used when you state the result.THD+N is typically measured and reported in a 20 Hz20 kHz bandwidth.14精选课件AP introductionHarmonic Distortion ConceptsHarmonic Distortion Concepts-Level and THD+NThe measured THD+N of a device will also vary with level and the frequency of the applied signal.Audio THD+N is typically measured and reported at a mid-range frequency(1 kHz or so)at the either the devices nominal operating level or at its maximum output level(MOL).-A THD+N versus frequency sweep or a THD+N versus amplitude sweeps will show how a DUT performs under varying stimulus.15精选课件THD+NHeadphone outputHeadphone output16精选课件THD+NTHD+N vs LevelTHD+N vs Level17精选课件THD+NTHD+N vs LevelTHD+N vs Level18精选课件THD+NHeadphone outputHeadphone output19精选课件THD+NHeadphone outputHeadphone output20精选课件THD+NHeadphone outputHeadphone output21精选课件THD+NHeadphone outputHeadphone output22精选课件 Thank you!23精选课件