Abstract: After the digital transformation of the section transmission, the transmitter often has high-end curtain grid over-load and high-end sag flow over-load phenomenon, and the orban CAM-1 audio processor is improved to filter out the ultra-low frequency below 20 Hz. The audio signal makes the transmitter work more stable.
Keywords: digital signal; audio processor; audio signal; ultra low frequency; high pass filter
0 Introduction In the field of broadcast technology, in order to minimize the nonlinear distortion added by audio processing, the advanced audio processor is used to process the signal. The audio processor has the functions of compression and limiting of the audio signal. In addition, various frequency top corrections can be performed, the program level is automatically adjusted, and the program signal is asymmetrically processed by phase processing. The use of the audio processor not only improves the listening loudness of the broadcast and prevents the over-modulation of the transmitter, but also improves the sound quality and significantly improves the broadcast quality.
1 orban CAM-1 audio processor improvement reasons and analysis In recent years, the bureau has carried out digital transformation of the transmission and reception of the transmitted signal, so that the broadcast quality and effect of the broadcast has been greatly improved. After the digital transformation of the festival, our platform has obviously improved the listening effect, but it also has a problem. In the past, when the analog signal was used, the eight transmitters in my computer room were working normally, but the machine often appeared high after using the digital signal. Curtain over-load and high-end sag flow (orban CAM-1 audio processor for 8 machines in our computer room), we have taken new equipment to ground, adjust the input and output levels of digital-to-analog converters and audio processors, etc. Various measures and means did not work, but the overload phenomenon disappeared after replacing the orban9200 audio processor. After analysis and test, it is judged that the transmission and reception of the transmitted signal is digitally modified and the frequency band of the output signal is widened. Relatively speaking, the transmitter is put forward higher requirements, and the orban CAM-1 audio processor is 20 Hz. The following signals are not processed, and the ultra-low frequency signal causes the machine to be unbearable and cause an overload. The orban9200 audio processor itself comes with a bandpass filter from 50 Hz to 8 kHz, which filters out the ultra-low frequency that causes the machine to overload. Therefore, the transmitter of the orban9200 audio processor is digitally modified after the transmission. There is no overload phenomenon. Later, we improved the input circuit of the orban CAM-1 audio processor itself, and connected a capacitor into a high-pass filter. The cutoff frequency was set at 50 Hz and the machine was running normally.
2 orban CAM-1 audio processor amplitude / frequency characteristics analysis orban CAM-1 audio processor amplitude / frequency characteristics shown in Figure 1.
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A 100 mV sine wave signal is input to the input of the audio processor. The relationship between the output voltage and the frequency is shown in Table 1.
It can be seen from the analysis of Fig. 1 and Table 1 that the audio processor has no filtering function for the ultra low frequency signal below 20 Hz which can cause the machine to be overloaded, and the 100 kWPSM transmitter is particularly sensitive to the ultra low frequency signal, thus causing frequent overload of the machine.
3 Circuit Improvement The improved circuit is shown in Figure 2 (the dotted line is the circuit with the audio processor input itself).
It can be seen from the above function that this circuit is a passive high-pass filter, and the data is brought into f0=50Hz. Its amplitude-frequency characteristic diagram is shown in Figure 3.
4 Improved test comparison analysis After adding a 0.6μ capacitor, a 100mV sine wave signal is also input at the input end of the audio processor. The relationship between output voltage and frequency is shown in Table 2.
After the input loop of the orban CAM-1 is connected in series with a 0.6 μ capacitor, the cutoff frequency of the high-pass filter is designed to be f0=50 Hz, which is basically consistent with the theoretical calculation by actual measurement.
5 Summary After the circuit is improved, there is no high-end curtain grid over-load and high-end sag over-current caused by ultra-low frequency audio signals below 20 Hz, and the transmitter work is more stable and the broadcast effect is better.
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