This article refers to the address: http://
| In FM broadcasting, since the power distribution of each frequency band in the signal is different, the level of the music program changes greatly as compared with the language type program. 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 allocation of the levels of each frequency band in the program, improve the average modulation degree of the signal, improve the listening effect, and improve the equal loudness. The following is an example of the audio 225 type audio processor. Talk about the debugging and application of audio processing in FM radio. I. Debugging of the audio processor The core of the MIDI 225 audio processor is an automatic gain control (AGC) circuit. Because the processor uses pulse width modulation (PWM) feedforward technology, 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 technique. That is to say, under the condition that the listener barely notices the distortion, the control of the input dynamic range is completed. For the other features of the processor, the description will not be repeated here. 1. Input gain setting Step 1 Feed the 500Hz sine wave signal directly to the left channel input of the unit via a mixer or other device. Step 2 precisely adjusts the test signal level, which should be 1.5 dB greater than the normal "0" program reference level. A. If the actual input value of the OVU when the mixer head indicates OVU is +8dBm, the signal sent to the left channel should be +9.5dBm. If the corresponding value of OVU is +4dBm, then the left channel should be sent. It is +5.5dBm. B. If a peak level meter is used, it is 1.5 dBm higher than the "measurement" level. Step 3 Adjust the “Left Input Gain†knob of the unit until the 0° and -3dB indicators of the slow AGC gain indicator light up at the same time. This step must be very slow because the correction response of the slow AGC is very slow. Step 4 Move the test signal from the left channel to the right channel and repeat steps 2 and 3. Step 5: Reduce the 500Hz test signal to the normal value (OVU). At this time, the slow AGC0dB indicator should remain lit. Only the left channel of the input left channel is lit, and the right channel is only illuminated by the right lamp. 2. Input level adjustment This process is very easy, using a radio-specific modulation meter, and a 500Hz sine wave test signal from the mixer, and then adjusting the output level to achieve a known 100% modulation, the required line output. level. Step 1 uses a 500HzOVU sine wave test signal from the audio mixer to send to the 255 type left input channel. If the input gain adjustment is appropriate, the 0dB indicator of the slow AGC is illuminated. Step 2 Add a 255-type three-band driver knob until the 10dB indicator of the mid-band dynamic gain attenuation is on. Step 3 Adjust the “Left†channel output level knob and monitor it with the modulation meter so that its modulation degree is 100%, or adjust to the line output level corresponding to 100% modulation. Step 4 moves the 500 Hz test signal from the left channel to the right channel. At the same level, there should be no difference between the gain LED of the slow AGC and the LED of the IF dynamic gain attenuation and the left channel. Step 5 Adjust the output knob of the right channel. Both methods can be used. One is to make the modulation table of the transmitter 100% modulation, or to read the line output level corresponding to 100% modulation. Step 6 simultaneously drive the left channel and right channel two-way dynamic gain attenuation indicator is still kept at 10dB light, the transmitter modulation is still 100% 3. The processor improves the sound quality setting of 7 knobs These seven knobs respectively adjust the audio quality of the audio processor to improve the quality of the audio signal of the processed program, usually placed in the middle position, clockwise adjustment is to make the sound more exaggerated direction, counterclockwise adjustment is low. Therefore, generally no adjustment is needed. 2. Problems in audio processor applications 1. Line output and wiring The application of the processor in the FM broadcast is generally connected after the broadcast mixer, the line output of the audio processing is outputted as an electronic balance on the rear ledge, and the stereo device (transmitter) is driven in a balanced manner. The "+" and "-" on the line output are set for the same phase of the program. When connected to the input phase in-phase method, the output of the program signal is in phase with the input. If the successor device is connected to its unbalanced input, it should only be connected to "+" and "GND" (ground). Do not connect "-" to ground to avoid damage. 2. Pre-add important issues" In the broadcast program signal power, in most cases, the high-end audio is allocated to a small number, taking vocal as an example. If odBr stands for 1μw, 2.7KHz is about 13dB lower than 1000KHz. All the high-range audio components in the instrument are much lower than 1KHz. It is because of the large number of broadcast program signals, the high-frequency is lower than the intermediate frequency, and the FM modulation signal uses the pre-emphasis technique, although the actual broadcast is used. The high-frequency pre-emphasis increases the ratio of the original to the intermediate frequency in the amplitude, so that the listener feels the low-frequency shock through the de-emphasis circuit, and the intermediate frequency is large and the high-pitched sound is bright. Whether the pre-emphasis in the audio processor in the FM broadcast is applied depends on the application of the pre-emphasis in the exciter (Italian RVR) in the transmitter. Generally, the pre-emphasis should be used in the transmitter. In the audio processing and the transmitter, the pre-emphasis is used at the same time. The turning point of the pre-emphasis curve is in the 225 type audio processor, which has 50μs (European standard), 75μs (American standard) and "0", etc. In the 50μs pre-emphasis, the "0" audio processor should be selected in "0" mode (I have used 50μs pre-emphasis). These are some of the experiences of the 225 audio processor application. |
This speaker series is made from robust,virtually indestructible ABS enclosure,and adjustable metal bracket offering maximum protection against shock and weather making it ideal for mounting in extreme outdoor conditions.
It can provide public address announcements and remote paging via network video surveillance applications.
Ideal for remote monitoring applications,such as at factories, building sites,
airports and shopping centres or in exposed outdoor installations.
With volume control
All are fitted with a sturdy,adjustable mounting bracket.
Horn Speaker Monitor,Monitor horn,Monitor horn speaker,Horn Speaker for Remote Monitoring Applications,Monitor horn speakers
Taixing Minsheng Electronic Co.,Ltd. , https://www.ms-speakers.com