Audio Line Test Standards

BS 6328-1-1985 Connection Equipment for Dedicated Lines in the UK Communication Network. Part 1: Specification for Audio Line Connection Devices

Common test indicators for audio equipment mainly include Level, FrequencyResponse, Total Harmonic Distortion plus Noise (THD+N), Signal to Noise Ratio (SNR), Crosstalk, and other parameters.

. In addition, there are some indicators such as phase and dynamic range. Level: The commonly used test levels in audio device testing include the following: ① given output level, such as 1V, 1W, or unit gain; ② A level that can generate fixed distortion, such as 1% THD+N; ③ The working level of the equipment is low in noise while also having appropriate dynamic margin; ④ Test the input or output level specified in the document. When testing, appropriate levels should be selected according to different situations to measure equipment, so it is necessary to first be very clear which level one should use. So how can I find the level that I should use to beat myself? This depends on the performance of DUTs (Device under test). For gain adjustable DUTs, the specified test level can be output by adjusting the gain. However, fixed gain DUTs cannot be output by adjusting the gain. Therefore, this article introduces how fixed gain DUTs can output the specified level. If the DUT is required to output a signal of 1Vrms, use the AP's Signal Generator to output a 1KHz sine signal, set the Level unit in the AP's Analyzer window to V, and then adjust the output amplitude of the signal generator so that the Level value in the Analyzer becomes 1V; For testing situations that require a DUT output of 1W, the method for finding the input level is similar, simply selecting the unit of Level as W; Of course, to obtain a 1% THD+N input signal, you need to select Function Reading as THD+N Ratio in the Analyzer window. Frequency Response: Frequency response measurement observes the output level generated by different frequency levels input to the tested device, and is an evaluation standard for the frequency response ability of the digital to analog to digital converter within the audio device. Usually, a constant amplitude sine wave is used to scan from extremely low frequency to extremely high frequency input to the device. If the response of the device is very flat, the reflection on the frequency response curve should be the average output of all frequencies, with almost no change in the trajectory line and a slope close to zero. The simplest full frequency response measurement can only select extremely low or extremely high intermediate frequencies within the frequency band to be tested. If the input levels of these frequencies are the same, the output level of the tested device represents its actual response to these frequencies. In the low-frequency and high-frequency parts, signal reconstruction is relatively difficult, so there is usually attenuation in these two frequency bands. The better the output quality of the device, the flatter the frequency response curve. Conversely, not only does it decay quickly at high and low frequencies, but it may also exhibit jitter in the general frequency band. Total Harmonic Distortion plus Noise (THD+N): Harmonic distortion is the addition of some additional frequency signal in the audio signal, and the harmonic frequency is an integer multiple of the original signal. Total harmonic distortion is the sum of all measurement results for the harmonics of the tested equipment. Before FFT, it was difficult to measure one's own THD without adding noise. Adding noise made it relatively easier and made it operable. In addition, the value of THD+N is convenient and objective, making it widely accepted by the public. THD+N will vary depending on the measurement bandwidth, so it is necessary to use high pass and low pass filters to limit the measurement bandwidth, and indicate the actual bandwidth used during testing in the results section. The commonly used bandwidth range is 20Hz to 20kHz. THD+N also varies with the level and frequency of the applied signal. So typically, equipment is measured using an intermediate frequency signal of approximately 1kHz and standard operating or output levels. Crosstalk: In multi-channel audio systems, it is common for signals from one channel to leak into another channel in a low-level manner. This type of signal that leaks across channels is called crosstalk, which is usually expressed as the ratio between the leaked signal and the original signal. Crosstalk is very difficult to eliminate in actual devices. Crosstalk is mainly the result of capacitive coupling between device channel conductors, and typically exhibits an increasing characteristic with increasing frequency. The crosstalk result is usually just a single number. However, conducting frequency sweep testing on the device can objectively reflect its actual crosstalk performance within the working bandwidth

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