AudioPrecision音频分析仪测试介绍.ppt

AP Introduction & THD + N,Analyzer input and XLR connector AP Panel Audio specifications THD + N,AP introduction,Analyzer input cable connection - Single ended output (MP3 headphone) 2 Signal, 3 Ground. e.g., Channel A: 2 Left output, 3 Ground Channel B: 2 Right output, 3 Ground - Differential output (loudspeaker) 2 Non-inverting signal, 3 Inverting signal,AP introduction,XLR Connector,AP introduction,XLR 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.,AP introduction,AP1 Panel,AP introduction,THD + N vs Level Curve,AP introduction,Analyzer Panel,AP introduction,Sweep Definitions Panel,AP introduction,Frequency 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.,AP introduction,Signal 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.,AP introduction,Crosstalk - 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.,AP introduction,Harmonic 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.,AP introduction,Harmonic 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.,AP introduction,Harmonic Distortion Concepts - Bandwidth and THD+N The 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 Hz“20 kHz bandwidth.,AP introduction,Harmonic Distortion Concepts - Level and THD+N The 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 DU