Application Analysis of Digiin Digital Frequency Hopping Wireless Microphone in Teaching Amplification
Abstract: The shortcomings of frequency-shifting power amplifier, V / U wireless microphone and infrared wireless microphone are analyzed. It is proposed to apply frequency hopping transmission technology to design a wireless microphone to amplify the lecturer's voice, avoiding the crosstalk problem of traditional V / U segment wireless microphones, and due to the use of digital voice signals for high-speed transmission, high-fidelity voice is achieved Degree of reduction. Proved by practical application, the DIGIIN digital frequency hopping wireless microphone developed and designed by this method is small in size, light in weight, low in power consumption, free from crosstalk, and rechargeable. It is a new type of special microphone for teaching that is popular among educators. Improve the current application level of multimedia classroom sound reinforcement system.
Keywords: HFSS; digital voice processing; 2.4GHz wireless transmission.
introduction
Because the teacher often teaches loudly, throat disease becomes an occupational disease that surrounds the teacher. According to the survey, more than 70% of the teachers suffer from pharyngitis, so the public address system for teaching has become one of the important tools for teachers to reduce the intensity of teaching.
As we all know, it is well known that frequency-shifting and sound-increasing is to continuously avoid the influence of the peak point of the room by changing the frequency of the input voice signal, thereby destroying the conditions that constitute acoustic feedback, and ultimately achieving the purpose of preventing howling, the sound must be distorted by the frequency shifter The result is poor sound quality, detrimental to the hearing of students, especially primary and middle school students. For this reason, the frequency shift power amplifier is currently in a phase-out phase.
In the more than ten years since the beginning of the development of multimedia education in the 1990s, due to price and management issues, there are actually few classrooms that use wireless microphones in education-specific sound reinforcement systems. Instead, a large number of frequency-shifting power amplifiers have been used for teaching expansion sound. In the 21st century, the domestic V / U segment wireless microphone technology has become very mature, and the price has fallen to the range of civilian products, but it still cannot replace frequency-shifting power amplifiers for teaching amplification. The reason is that the traditional V / U used for teaching at this stage Duan wireless microphone not only solves the problem of teacher's sound reinforcement in class, but also reflects some of its irreversible shortcomings, which cannot be widely promoted in the teaching industry.
Analysis of V / U wireless microphone and infrared wireless microphone
At present, the main disadvantages of teaching V / U wireless microphones are as follows:
1) Heavy and bulky. Holding the microphone can't free the teacher's hands, and the lavalier microphone has a problem of being difficult to wear, especially for female teachers.
2) High battery consumption cost. If a pair of microphones use a pair of AAA batteries for 6 hours a day, excluding holidays, and use 180 days per year, the annual cost is 3 × 180 = 540 yuan, which does not include equipment maintenance costs.
3) High failure rate. The batteries are replaced frequently, so the microphone battery box cover and battery reed are easy to wear; the connection between the microphone transmitter and the pickup is also prone to failure.
4) Easy to cross. In teaching applications, it is very common to use dozens or even hundreds of microphones in the same campus at the same time. The current U-band microphone can only provide one hundred or dozens of frequency points, so the phenomenon of crosstalk is serious.
5) Difficult to manage. Due to the fixed frequency point, the transmitter and receiver must use the frequency and purchase accessories, which is very inconvenient. It is even more impossible to assign the transmitter to individual teachers for their own use and management.
In response to the above problems, various manufacturers have made improvements, such as the method of scanning frequency points after power-on, so they can arbitrarily frequency-match, but their frequency points remain unchanged after locking, and are also prone to crosstalk. The second is the infrared wireless microphone, whose infrared transmission method can solve the problems of crosstalk and free matching. However, infrared light waves are extremely easy to be blocked. In actual use, even the teacher's hand-waving action can cause the sound to be cut off, which is not very practical.
Frequency hopping technology
The frequency hopping communication technology (FHSS) was first used by the US military for encrypted communications on the battlefield. The principle is that the transmitting and receiving parties continuously change the communication frequency band according to a certain rule, and extend the narrow-band signal to a certain wide frequency band for transmission. Means of spread spectrum communication. The basic concept is as follows:
ï® The bandwidth of the transmitted signal is much greater than the minimum bandwidth necessary for the transmitted information
ï® The widening of the frequency band is realized by the expansion function (coding and modulation), which has nothing to do with the transmitted information and data, and only the transmitter and receiver know
ï® At the receiving end, the same spreading code is used for related demodulation to despread and recover the transmitted information data
Frequency hopping technology can be seen as the following two processes:
ï® The data is modulated onto the wireless carrier.
ï® The center frequency of the wireless carrier is carried on the basis of the "extended sequence".
Effect of frequency hopping spread spectrum:
ï® The data is carried by all frequency hopping points.
ï® If the noise does not affect all frequency hopping points, the information can be repaired.
ï® Under certain conditions, multiple systems can coexist in the same frequency range.
Design of DIGIIN digital frequency hopping wireless microphone
The frequency hopping wireless microphone designed in this paper is a completely digital microphone. The transmitter's electret microphone signal (voice) is converted into a digital audio signal by an audio AD converter, and then these digital signals are packaged using a high-speed MCU (or DSP). Finally, it is modulated to the 2.4GHz ISM frequency band and transmitted to the receiver using frequency hopping. After the receiver processes the signal stream, it converts the audio signal into an analog signal through a DA converter and transmits it to the audio power amplifier for amplification. Due to the use of two-way communication, the transmitter and receiver can use address code identification, locking and other software means to achieve automatic matching and arbitrary matching of the transmitter and receiver. Moreover, the use of high-speed embedded systems and DSP systems can sample, process, and transmit voice signals up to 96k, 24bit, so the voice effect reaches high fidelity quality.
DIGIIN digital frequency hopping wireless microphone software and hardware systems, communication protocols, and voice algorithms are all independent intellectual property rights of the producer. Therefore, the entire system can be developed for teaching applications and is very suitable for educators. Its performance is as follows:
Low radiation: It is one eighth of the international standard. The professional antenna lobe design and adaptive power algorithm make the radio coverage and power radiation just right, which can not only meet the requirements of sound reinforcement in the classroom, but also provide low radiation transmission.
The antenna is easy to install: the antenna can be installed in front of the podium or near the blackboard. There is no need to install it on the roof of the classroom.
Radio intelligent matching mode: The transmitter can be automatically recognized by the receiver within half a meter of the antenna. Any transmitter can be matched with any receiver. After matching, it is automatically locked until the transmitter is turned off or leaves the radio coverage (you can also press the receiver matching key to force Rematch).
No crosstalk: Frequency-hopping communication method, intelligent matching, more than 1000 devices used in the same school (different classrooms) at the same time without crosstalk.
High-fidelity sound quality: 32-96K, 16-24Bit voice digital signal, built-in adjustable digital voice equalizer.
Saving: Lithium battery power supply, can be used continuously for 8-10 hours on one charge.
Small: The transmitter is two fingers wide and one finger high, 45 grams.
Easy to wear: Practical design with integrated pickup head, case, and buckle, which can be directly clipped on and used with a lanyard.
Cheap is good for popularization: Through optimized design, the processing task is moved to the receiver as much as possible, which greatly reduces the cost of the transmitter.
New application mode of teaching microphone: teachers have a transmitter, keep it by themselves, clean and hygienic, and use it wherever they go.
Conclusion
This article proposes a method to improve the current teaching wireless microphone, using frequency hopping spread spectrum communication technology, digital voice technology to design a new generation of teaching wireless microphone, is an innovative idea to improve the current teaching public address system. This solution has been applied to the DIGIIN DF series of digital wireless frequency hopping microphones, which is very popular among educators.
References
1. Hu Zhongyu, chief editor, Modern Shortwave Communication, National Defense Industry Press, 2005.1
2. Lu Guanming, Zong Fang, Principles and Applications of Digital Audio, Machinery Industry Press, 2005.1
3. (U.S.) Ludwig (Rudwig, R.) waiting, translated by Wang Ziyu. Radio Frequency Circuit Design-Theory and Application, Electronic Industry Press, 2002.5
Abstract: The shortcomings of frequency-shifting power amplifier, V / U wireless microphone and infrared wireless microphone are analyzed. It is proposed to apply frequency hopping transmission technology to design a wireless microphone to amplify the lecturer's voice, avoiding the crosstalk problem of traditional V / U segment wireless microphones, and due to the use of digital voice signals for high-speed transmission, high-fidelity voice is achieved Degree of reduction. Proved by practical application, the DIGIIN digital frequency hopping wireless microphone developed and designed by this method is small in size, light in weight, low in power consumption, free from crosstalk, and rechargeable. It is a new type of special microphone for teaching that is popular among educators. Improve the current application level of multimedia classroom sound reinforcement system.
Keywords: HFSS; digital voice processing; 2.4GHz wireless transmission.
introduction
Because the teacher often teaches loudly, throat disease becomes an occupational disease that surrounds the teacher. According to the survey, more than 70% of the teachers suffer from pharyngitis, so the public address system for teaching has become one of the important tools for teachers to reduce the intensity of teaching.
As we all know, it is well known that frequency-shifting and sound-increasing is to continuously avoid the influence of the peak point of the room by changing the frequency of the input voice signal, thereby destroying the conditions that constitute acoustic feedback, and ultimately achieving the purpose of preventing howling, the sound must be distorted by the frequency shifter The result is poor sound quality, detrimental to the hearing of students, especially primary and middle school students. For this reason, the frequency shift power amplifier is currently in a phase-out phase.
In the more than ten years since the beginning of the development of multimedia education in the 1990s, due to price and management issues, there are actually few classrooms that use wireless microphones in education-specific sound reinforcement systems. Instead, a large number of frequency-shifting power amplifiers have been used for teaching expansion sound. In the 21st century, the domestic V / U segment wireless microphone technology has become very mature, and the price has fallen to the range of civilian products, but it still cannot replace frequency-shifting power amplifiers for teaching amplification. The reason is that the traditional V / U used for teaching at this stage Duan wireless microphone not only solves the problem of teacher's sound reinforcement in class, but also reflects some of its irreversible shortcomings, which cannot be widely promoted in the teaching industry.
Analysis of V / U wireless microphone and infrared wireless microphone
At present, the main disadvantages of teaching V / U wireless microphones are as follows:
1) Heavy and bulky. Holding the microphone can't free the teacher's hands, and the lavalier microphone has a problem of being difficult to wear, especially for female teachers.
2) High battery consumption cost. If a pair of microphones use a pair of AAA batteries for 6 hours a day, excluding holidays, and use 180 days per year, the annual cost is 3 × 180 = 540 yuan, which does not include equipment maintenance costs.
3) High failure rate. The batteries are replaced frequently, so the microphone battery box cover and battery reed are easy to wear; the connection between the microphone transmitter and the pickup is also prone to failure.
4) Easy to cross. In teaching applications, it is very common to use dozens or even hundreds of microphones in the same campus at the same time. The current U-band microphone can only provide one hundred or dozens of frequency points, so the phenomenon of crosstalk is serious.
5) Difficult to manage. Due to the fixed frequency point, the transmitter and receiver must use the frequency and purchase accessories, which is very inconvenient. It is even more impossible to assign the transmitter to individual teachers for their own use and management.
In response to the above problems, various manufacturers have made improvements, such as the method of scanning frequency points after power-on, so they can arbitrarily frequency-match, but their frequency points remain unchanged after locking, and are also prone to crosstalk. The second is the infrared wireless microphone, whose infrared transmission method can solve the problems of crosstalk and free matching. However, infrared light waves are extremely easy to be blocked. In actual use, even the teacher's hand-waving action can cause the sound to be cut off, which is not very practical.
Frequency hopping technology
The frequency hopping communication technology (FHSS) was first used by the US military for encrypted communications on the battlefield. The principle is that the transmitting and receiving parties continuously change the communication frequency band according to a certain rule, and extend the narrow-band signal to a certain wide frequency band for transmission. Means of spread spectrum communication. The basic concept is as follows:
ï® The bandwidth of the transmitted signal is much greater than the minimum bandwidth necessary for the transmitted information
ï® The widening of the frequency band is realized by the expansion function (coding and modulation), which has nothing to do with the transmitted information and data, and only the transmitter and receiver know
ï® At the receiving end, the same spreading code is used for related demodulation to despread and recover the transmitted information data
Frequency hopping technology can be seen as the following two processes:
ï® The data is modulated onto the wireless carrier.
ï® The center frequency of the wireless carrier is carried on the basis of the "extended sequence".
Effect of frequency hopping spread spectrum:
ï® The data is carried by all frequency hopping points.
ï® If the noise does not affect all frequency hopping points, the information can be repaired.
ï® Under certain conditions, multiple systems can coexist in the same frequency range.
Design of DIGIIN digital frequency hopping wireless microphone
The frequency hopping wireless microphone designed in this paper is a completely digital microphone. The transmitter's electret microphone signal (voice) is converted into a digital audio signal by an audio AD converter, and then these digital signals are packaged using a high-speed MCU (or DSP). Finally, it is modulated to the 2.4GHz ISM frequency band and transmitted to the receiver using frequency hopping. After the receiver processes the signal stream, it converts the audio signal into an analog signal through a DA converter and transmits it to the audio power amplifier for amplification. Due to the use of two-way communication, the transmitter and receiver can use address code identification, locking and other software means to achieve automatic matching and arbitrary matching of the transmitter and receiver. Moreover, the use of high-speed embedded systems and DSP systems can sample, process, and transmit voice signals up to 96k, 24bit, so the voice effect reaches high fidelity quality.
DIGIIN digital frequency hopping wireless microphone software and hardware systems, communication protocols, and voice algorithms are all independent intellectual property rights of the producer. Therefore, the entire system can be developed for teaching applications and is very suitable for educators. Its performance is as follows:
Low radiation: It is one eighth of the international standard. The professional antenna lobe design and adaptive power algorithm make the radio coverage and power radiation just right, which can not only meet the requirements of sound reinforcement in the classroom, but also provide low radiation transmission.
The antenna is easy to install: the antenna can be installed in front of the podium or near the blackboard. There is no need to install it on the roof of the classroom.
Radio intelligent matching mode: The transmitter can be automatically recognized by the receiver within half a meter of the antenna. Any transmitter can be matched with any receiver. After matching, it is automatically locked until the transmitter is turned off or leaves the radio coverage (you can also press the receiver matching key to force Rematch).
No crosstalk: Frequency-hopping communication method, intelligent matching, more than 1000 devices used in the same school (different classrooms) at the same time without crosstalk.
High-fidelity sound quality: 32-96K, 16-24Bit voice digital signal, built-in adjustable digital voice equalizer.
Saving: Lithium battery power supply, can be used continuously for 8-10 hours on one charge.
Small: The transmitter is two fingers wide and one finger high, 45 grams.
Easy to wear: Practical design with integrated pickup head, case, and buckle, which can be directly clipped on and used with a lanyard.
Cheap is good for popularization: Through optimized design, the processing task is moved to the receiver as much as possible, which greatly reduces the cost of the transmitter.
New application mode of teaching microphone: teachers have a transmitter, keep it by themselves, clean and hygienic, and use it wherever they go.
Conclusion
This article proposes a method to improve the current teaching wireless microphone, using frequency hopping spread spectrum communication technology, digital voice technology to design a new generation of teaching wireless microphone, is an innovative idea to improve the current teaching public address system. This solution has been applied to the DIGIIN DF series of digital wireless frequency hopping microphones, which is very popular among educators.
References
1. Hu Zhongyu, chief editor, Modern Shortwave Communication, National Defense Industry Press, 2005.1
2. Lu Guanming, Zong Fang, Principles and Applications of Digital Audio, Machinery Industry Press, 2005.1
3. (U.S.) Ludwig (Rudwig, R.) waiting, translated by Wang Ziyu. Radio Frequency Circuit Design-Theory and Application, Electronic Industry Press, 2002.5
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