Transmission and application of the hottest audio

2022-07-25
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Transmission and application of audio processor in FM broadcasting

in FM broadcasting, due to the different power distribution of each frequency band in the signal, the level of music programs changes greatly compared with language programs. When the level is small, the signal-to-noise ratio is poor, and when the level is large, it is easy to cause distortion. Therefore, the application of the audio processor will greatly improve the level distribution of each frequency band in the program, improve the average modulation of the signal, improve the listening effect, and improve the equal loudness. Next, take the yinwanli 225 audio processor as an example to talk about the debugging and application of audio processing in FM broadcasting

I Debugging of audio processor

the core of yinwanli 225 audio processor is the automatic gain control (a.g.c) circuit. Because the processor adopts the feedforward technology of pulse width modulation (PWM), the function of the processor is smoother and softer. The total amount of control in processing the input dynamic range is also much larger than the traditional negative feedback technology. That is to say, under the condition that the listener hardly detects the distortion, the control of the input dynamic range is completed. This paper will not repeat other features of the processor, and the debugging in the application will be discussed below

1. Input gain setting

step 1 directly feed 500Hz sine wave measurement signal to the left channel input of the machine through the mixer or other equipment

step 2 accurately adjust the test signal level, which should be 1.5dB greater than the normal 0 program reference level

a. if the actual value of input level when ovu is indicated by the meter head of the mixer is +8dbm, the signal sent to the left channel should be +9.5dbm. If the corresponding value of ovu is +4dbm, the signal sent to the left channel should be +5.5dbm

b. if the peak level meter is used, it shall be 1.5dbm higher than the measured level

step 3 adjust the local left input gain knob until the slow a.g.c. gain indicator lights 0dB and -3db are on at the same time

this step must be very slow, because the correction response of the slow a.g.c. is very slow

step 4 move the test signal from the left channel to the right channel, and repeat steps 2 and 3

step effective stretching space interval: 0 ⑺ 00mm, overall dimension of equipment host (length × wide × Height): 750 × five hundred and thirty × 1820 (mm) step 5 reduce the 500Hz test signal to the normal value (ovu). At this time, the slow a.g.c.0db indicator should remain on. Only the left light is on for the input left channel, and only the right light is on for the input right channel

2. Input level adjustment

this process is very easy. Use the special modulation meter of the radio station and the 500Hz sine wave test signal from the mixer, and then adjust the output level to the required line output level when the known 100% modulation can be achieved

step 1 use a 500hzovu sine wave test signal from the audio mixer to send it to the 255 type left input channel. If the input gain is adjusted properly, the 0dB indicator of the slow a.g.c will be on

add 255 in step 2. Use the medium-sized tri band driver knob in the process until the 10dB indication of dynamic gain attenuation in the intermediate frequency band is on.

step 3 adjust the left channel output level knob and use the modulation meter to monitor it, so that its modulation degree is 100%, or adjust it to the line output level corresponding to 100% modulation degree

step 4 move the 500Hz test signal from the left channel to the right channel. At the same level, there should be no difference between the slow a.g.c. gain LED or the if dynamic gain attenuation led and the left channel

step 5 adjust the output knob of the right channel. Two methods are available. One is to make the modulation meter of the transmitter 100% modulated, or read out the line output level corresponding to 100% modulation

step 6: drive the dynamic gain attenuation indicator of both left and right channels at the same time. The indicator remains on at 10dB, which can effectively enrich and grab harmful heavy metal elements in the soil. The transmitter adjustment is still 100%

3 Setting of 7 knobs for the processor to improve the sound quality

these 7 knobs respectively adjust the sound quality controlled by the audio processor to improve the audio signal quality of the processed program. They are usually placed in the middle position. Clockwise adjustment is to make the sound more exaggerated. Counterclockwise adjustment is 3 The working frequency of the experimental machine is not higher than 500 times/minute, which is a low tendency. Therefore, it generally does not need to be adjusted

II Problems in audio processor application

1 Line output and wiring

the application of processor in FM broadcast is generally connected after the broadcast mixer. The line output of the audio processing is electronically balanced on the rear pull wiring rack to drive the stereo equipment (transmitter) in a balanced manner. The + and - on the line output end are set for the same phase of the program ground. When connected with the same phase method at the input end, the output of the program signal is in phase with the input. If the follow-up equipment is single terminated with its unbalanced input, it should only connect + and GND (ground), and do not connect - to the ground, so as to avoid damage

2. Pre added important problem

in the signal power of broadcast programs, in most cases, the high-end audio is allocated to a small number. For example, if odbr represents 1 W, it is 2.7khz, about 13dB lower than 1000khz. All high-frequency components in the musical instrument are much lower than 1kHz by dB. It is precisely because in the vast number of broadcast program signals, the level of high-frequency is lower than that of intermediate frequency that FM modulation signals adopt pre emphasis technology. In actual broadcasting, although high-frequency pre emphasis is adopted, the original proportion to intermediate frequency is completely maintained in amplitude, so that listeners feel the shock of low-frequency through the past emphasis circuit. The intermediate frequency is grand and the high pitched is bright. The application of pre emphasis in the audio processor in FM broadcasting depends on whether there is pre emphasis in the exciter (Italian RVR) in the transmitter. Generally, pre emphasis should be used in the transmitter. Note that pre emphasis cannot be used in both audio processing and the transmitter. The turning point of the pre emphasis curve is in the 225 audio processor, which has three modes: 50 s (European standard), 75 s (American Standard) and 0, If 50 s pre emphasis is used in the transmitter, the 0 mode should be selected in the 225 audio processor (I used 50 s pre emphasis)

the above is some experience of the application of 225 audio processor

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