Audio-Precision音频分析仪测试介绍演示教学课件.ppt

1、1AP Introduction&THD+N Analyzer input and XLR connector AP Panel Audio specifications THD+N2AP introduction Analyzer 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 ou

2、tput,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 signalsignal3AP introduction XLR ConnectorXLR

3、Connector4AP introduction XLR 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,

4、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.5AP introduction A

5、P1 PanelAP1 Panel6AP introduction THDTHD +N vs LevelN vs Level CurveCurve7AP introduction Analyzer PanelAnalyzer Panel8AP introduction Sweep DefinitionsSweep Definitions PanelPanel9AP introduction Frequency ResponseFrequency Response-Frequency Response measurements are made by stepping or sweeping a

6、 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

7、 values for START and STOP under SWEEP(F9)DEFINITIONS panel.10AP introduction Signal 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 calibrate

8、d as the 0 dBr reference of the analyzer.Then the residual output amplitude(noise)is measured and expressed in dB relative to the reference.11AP introduction CrosstalkCrosstalk-Signals from one channel leaking into another channel.Normally,this happens between left and right stereo channels.-A gener

9、ator 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 si

10、gnal by the above-noted output test value,and the answer expressed in dB.12AP introduction Harmonic 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 distor

11、tion 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.13AP introduction Harm

12、onic 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 w

13、hich the fundamental component is removed by a bandreject(norch)filter and all remaining energy measured,including harmonics and noise.14AP introduction Harmonic Distortion ConceptsHarmonic Distortion Concepts-Bandwidth and THD+NThe measured THD+N of a device will vary with the measurement bandwidth

14、.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.15AP introduction Harmonic Distortion ConceptsHarmonic Distort

15、ion 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 TH

16、D+N versus frequency sweep or a THD+N versus amplitude sweeps will show how a DUT performs under varying stimulus.16THD+N Headphone outputHeadphone output17THD+N THD+N vs LevelTHD+N vs Level18THD+N THD+N vs LevelTHD+N vs Level19THD+N Headphone outputHeadphone output20THD+N Headphone outputHeadphone output21THD+N Headphone outputHeadphone output22THD+N Headphone outputHeadphone output23 Thank you!