The success of audio processing of a broadcast program is judged by its actual effect, that is, the auditory effect. For example, the broadcast effect of the broadcast can be accepted by the audience. This kind of processing is considered to be successful, otherwise it is a failure. In this regard, I will proceed from the principle of the audio processor, combined with the actual use situation, fully tap its potential advantages, and more effectively and rationally play its performance, should start from the following three aspects:
(1) Keep the signal undistorted
At the front end of the mid-wave broadcast transmitter, the audio signal highly processed by the audio processor will contain many flat-top waveforms similar to square waves. The square wave's waveform requires a relatively high amplitude and phase response to the transmission path it passes through. In principle, in the frequency range of the main energy of the program, if the flat amplitude and the group delay are deviated, the flattened top of the processed audio signal will be tilted, thereby increasing the peak modulation voltage, but the average level is not increased. . From the peak/flat ratio value, the average level of the path is reduced, and the loudness is correspondingly reduced. In this regard, we must maintain the original shape of the processed signal waveform. The first method is to select the transmission cable with high quality and excellent performance in the use of the transmission signal cable, and require small distribution parameters, frequency bandwidth, and thick wire diameter, low-loss, shielded copper core transmission line. This is very important and very effective. In addition, in the transmission connection, try not to add any additional equipment and branch components, such as intermediate amplifiers, distributors, etc., to reduce signal waveform distortion and ensure good transmission quality.
(2) Audio processing system settings
①For the audio processor, it consists of two circuits, one is a slow-moving AGC, and the other is a compressor with moderate motion and recovery time. The optimal time constant is adjusted for each frequency band as needed. We conclude in actual use that the time constant of the low-frequency band is set to be slower than the high-frequency band (about 200 μs), which has a greater effect on increasing the signal density of the program.
② The audio processor adds some additional components to the basic system, enabling the audio processor to install the frequency equalization processing component between the slow AGC and the multi-band compressor to compensate for the typical sound of the medium wave broadcast signal frequently audible conditions. Appropriately increase the distribution of 600HZ-1.2KHZ sound energy throughout the audio spectrum, making this sound audible "larger" (the most sensitive range of human hearing is 2KHZ-8KHZ). It can make the audience feel the sound is really beautiful.
③ We also use the “Attenuation Distortion” device on the audio processor to provide absolute negative peak control, which prevents audio signal spills and eliminates distortion in some frequency bands that the listener is most likely to hear. .
(3) The position where the audio processor is placed in the system is also placed in the position of the audio processor in the system, in order to effectively protect the peak-limited waveform processed by the audio processor, so that it is transmitted to There is no change in the process of the transmitter, the audio processor should be placed close to the transmitter, and the shorter the distance, the better. In order to avoid the variation of the distribution parameters during the transmission process, the parasitic modulation peak is caused, and the waveform whose peak limit has been processed is changed, resulting in distortion of the waveform of the audio signal.
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