Sinbosen

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 amplitude and phase response of the square wave's waveform to the transmission path it passes is relatively high. 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 have to maintain the prototype of the processed signal waveform. The first method adopted is to select a transmission cable with high quality and excellent performance in the use of transmission signal cable, and require a copper core transmission line with small distribution parameters, frequency bandwidth, small wire diameter, low attenuation, and good shielding performance.  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.

1. For 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 also adds some auxiliary components in the basic system, and the frequency equalization processing component of the audio processor installed between the slow moving AGC and the multi-band compressor is enabled to compensate for the typical sound of the medium wave broadcast signal. Frequently audible conditions. Appropriately increasing the distribution of 600Hz-1.2KHz sound energy throughout the audio spectrum makes this sound audibly "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 the audio signal from overflowing, eliminating distortion in some of the bands that the listener is most likely to hear.

In the system, the position where the audio processor is placed is also fastidious.In order to effectively protect the peak-limited waveform processed by the audio processor and prevent it from changing during transmission to 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 peak of the parasitic modulation is caused, and the waveform of the processed peak limit is changed, resulting in distortion of the waveform of the audio signal.

1. can solve the problem of large difference in program level caused by recording, exchange, different program content and using different recording and playback devices, which is difficult to solve manually when manually adjusting the program level.

2. Creates conditions for establishing a volume balance between language programs and music programs.

3. It is possible to amplify a weak signal at a low tide of the program so as not to be submerged by the noise. Usually, the level of the treble in the program is low, and after processing, it can be improved properly. The high-frequency not only determines the clarity of the program, but also has a mental and physiological complex relationship with the loudness, due to the improving of clarity, the audience feels it louder.

4. Stereo broadcast, which covers radius is half of the mono broadcast with the same power level and transmission condition. After the audio processor is used, due to the increase of the sideband wave power,it is possible to receive high-quality signals where the received carrier field is slightly lower than the requirement， and the coverage is expanded.

Audio source

Audio Mixer