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Common media such as discs, movies, and music have raised our standards for "good sound quality." However, the audio quality in distance learning classrooms is not so optimistic. Low-quality audio makes it difficult for students to understand the content of teacher presentation materials, and to some extent, reduces the enthusiasm of students to participate in the classroom. Low-quality classroom audio quality greatly inhibits the interactive discussion of students attending classes at different locations, because technical barriers hinder the quality of students' listening content, and as students, they are often reluctant to overcome this technical barrier and continue to do so. Work hard.
Students and teachers usually make some complaints. For example, the voice of the speaker is almost like the bottom of the barrel; when others are speaking, they often lose the content at the beginning; if they do not receive feedback or yell Sound, we can't hear clearly at all; when we spoke, we heard our own echo. These technical and operational issues are easy to generate for those who have not been trained in specific professional audio. Understanding some basic audio concepts can help designers, installers, and users of distance learning audio systems get higher quality audio in the classroom.
A complete distance learning classroom typically consists of four main components: a classroom, an audio system, a video system, and a set of transport network connectors. This article will focus on the various devices and audio systems in the classroom—determining the sound quality and the intelligibility of the audio content (understand the content of the story) in the various audiences that are transmitted to all locations in the classroom, as well as the various controls needed to control the various devices. The work is explained in detail.
Since the medium of sound transmission—fiber, satellite, and microwave—has a large impact on sound quality, and there has been a comprehensive discussion of these media, we will not discuss discussing these media again in this article. Advantages and disadvantages. We will discuss audio devices that complement the audio quality of certain transmission media.
Classroom sound vs. audio system 2. Classroom 1, classroom sound vs. audio system The sound that is transmitted to each student location begins with the classroom. The sound of the classroom—the way the classroom affects sound waves—is determined by physical factors, such as the size of the classroom, the materials used in classroom buildings, the surfaces of walls and floors, and so on. If the sound quality of the classroom itself is relatively poor, the sound picked up by the audio system and the audio quality transmitted to all parties will be blurred, causing auditory fatigue. In some more serious situations, the sound may not be recognized at all. It is difficult to teach interactively.
The classroom itself and the audio system have the most important impact on sound quality. To get clear audio quality, make the audio system produce flawless sound, and try to be user friendly, be sure to optimize the classroom sound and audio system design. However, in many cases, certain constraints limit certain conditions and are compensated by other optimizations. For example, if you have to use a classroom with poor sound performance due to conditions, you should try to ensure that the system has a high quality when designing the audio system. Similarly, if the budget constraints or user preferences make the audio system design impossible, then the classroom sound should meet very good conditions. If the low-quality audio system is paired with low-quality classroom sounds, the results can be imagined, teachers and students are very dissatisfied with the system, and ultimately do not want to use the system.
Classroom sound vs. audio system: If one side is defective, you need to optimize the other side to maintain the audio quality of the system. If you happen to be in the room where the speaker is located, you have to brain to combine the audio signals collected by the ear with the video signals collected by the eyes. The visual, auditory and brain functions allow you to make some noise or no effect. The sound is filtered and focused on the sound you want to hear (speaker's voice). However, microphones do not have this capability because, in order to pick up clearer, recognizable sounds, the microphone must have a pickup function that is more sensitive than human hearing. Then, some rooms have good sound quality and some are very poor. What is the reason? Can you know in advance which room has better sound quality and is more suitable for distance learning?
How to identify whether a classroom is suitable for distance learning 2
The sound of the classroom is determined by many factors. For our distance learning, there are two main aspects that have a major impact on the classroom sound: decay time and background noise level.
(1) Decay time Sound waves transmit the speaker's voice to all directions. Some are passed directly from the speaker to the microphone, and some are randomly distributed, passing through the wall, ceiling or floor. The reflected sound reaches the microphone for a longer time than the speaker directly reaches the microphone and mixes, which produces A continuous sound or a trailing of the original sound. The decay time indicates the period of time during which the reflected sound becomes weak or attenuated until it is inaudible. The debilitating time of the room is mainly determined by the size, shape and architecture of the room. In large marble churches, the decay time can be as long as 5 seconds, the concrete classroom is about 1-2 seconds, and the thicker carpet and curtain meeting rooms can be 1/2 second.
If the room's reflection is more serious, the sound that the microphone picks up in the room sounds like the speaker is talking at the bottom of the bucket, or like at the other end of the corridor. In short, the longer the decay time, the worse the sound quality will be.
The decay time is detected by a special test device that produces "white" and "red" color noise and then tests how long the sound lasts after the noise stops. The equipment is usually manufactured by a professional audio system installer or audio consultant for the evaluation of distance learning classrooms.
(2) Background noise volume Simply put, noise is any sound that the listener does not want to hear. Lower background noise can usually be compressed or eliminated by brain filtering, but this can blur the hearing. If the noise is constantly higher than the volume of the speech, an unrecognizable sound will be produced, setting the language to be lost. In the classroom, the noise sources that make the audience have difficulty in hearing are: the cooling fan of the computer and the projector above the head; the shaking duct system; the exhaust pipe produces the impact sound of the ear when the air flows; the classroom The sound of people crossing the corridor outside; the equipment in the room adjacent to the classroom; the hum of the fluorescent lights.
The background noise precision tester in the room can be manufactured using an instrument called an audio spectrum analyzer. The noise volume in the test unit device is expressed in units of "decibel", abbreviated as dB. Since the effects of different volume sounds on the human ear are different, the tester tests each of the different audible spectrums. The test results are compared to a standardized noise standard curve to determine if the room is suitable for a given target. The noise standard rate for rooms used for distance learning, conference calls, and the like should be below 35, which is a quieter environment.
There is also a device called a noise meter or sound pressure level indicator that provides an average index of the amount of noise in the room. Note that noise meters sold in community electronics stores often do not have the ability to detect low-spectrum noise (such as the hum of a ventilator), so the results of the classroom noise level are not accurate.
(3) How to improve the sound quality of the room In most classrooms, the audio quality needs to be improved. The most needed is to reduce the decay time of the room. This problem is solved by covering some commercial material interfaces (such as walls, floors, ceilings and windows) or using panels that absorb sound rather than reflecting sound or sound waves.
Background noise reduction is usually solved by repairing or replacing the light source equipment. It can also be adjusted by adjusting the air conditioning duct. However, the noise from the outside of the classroom is not easy to control. The footsteps in the corridor can be reduced by laying the carpet, and the speed is high. Traffic noise on the road or noise from nearby equipment may require the reconstruction of walls, ceilings or floors to be avoided. The cost of reducing noise from the outside to the inside is expensive. Without the help of an experienced audio consultant, it is recommended not to try this route. Perhaps the most sensible solution is to consider changing to a classroom.
Composition of the audio system III. Audio system 1. Composition of the audio system Audio equipment for distance learning usually selects different audio systems according to the size of the classroom, the arrangement of the seats and the topics taught, the financial budget and other factors. However, the following basic components of an audio device are universal: a wireless microphone used by the instructor; a microphone mounted on the desktop used by the student; a microphone mixer for controlling, balancing, and integrating the microphone signal; passing audio from another classroom to Amplifiers or multiple speakers in each room.
Some special information about different types of microphones and wireless microphone systems, such as how they work, how to choose the most suitable category, is done in Shure Brothers Incorporated's Guide to Better Audio. Complete narrative. Information about amplifiers and horns is also very detailed in the product descriptions of individual manufacturers.
Many viewers have been very impressed by the popularity of some popular spy movies such as James Bond and Sneakers. They are very surprised that such ordinary audio equipment can create such a miracle that can be picked up from a distance of 1 mile. The speech signal can also hide the microphone behind the ventilation device. Although a group of audio experts use a computer to extract discernible conversations from recordings over several months of work, this is unlikely in a live program. In a wide range of situations, modern audio systems can perform very well, but they can't compensate for the lack of audio. Noise and reflected audio cannot be eliminated once they are picked up or combined with the content of the speech.
Fortunately, there are some time-testing "rules" in audio system design that can minimize undesirable audio effects. Three aspects are especially important. If you ignore it, no matter how much time, how much money, and how much effort you make, it is basically impossible to achieve satisfactory audio quality.
3 factors that contribute to system performance or disrupt audio quality 2
(1) The distance from the speaker to the microphone The most important factor determining the performance of a distance learning audio system is the distance of the speaker to the nearest microphone. The farther the microphone is from the speaker, the lower the volume of the speech reaches the microphone. Therefore, the sensitivity of the microphone to “hearing†is increased, so that the microphone picks up more desired sounds, but also picks up more background noise. , reflected audio, etc. The farther the microphone is from the speaker, the louder the noise.
So, how far is it to be "too far" when installing a microphone? No matter which microphone is applied, no matter how it is installed, there is a certain distance from the microphone to the speaker's voice. This distance is called the critical distance, referred to as Dc. The critical distance of each room is different and is determined by the size of the room and the decay time.
Regardless of what device is added to the audio system or the audio system is adjusted, if the speaker's distance to the nearest microphone exceeds the critical distance, then his speech will be difficult to hear. Since most classrooms have a critical distance of 2-3 feet, when calculating the distance between the speaker and the microphone, the following criteria should be considered: less than 2 feet is ideal; 2-3 feet is better; 3-5 feet are barely More than 5 feet is not feasible. In a typical classroom, the distance between the microphone and the speaker should be less than 2 feet, and the distance is better than the distance. In most classroom audio systems, one of the most important ways to improve audio quality is to bring the microphone closer to the speaker.
The best place to install the microphone in the classroom We discussed the importance of the distance of the microphone from the speaker. So, where is the microphone installed to best pick up student questions? This problem is mainly determined by the way the classroom is used and the way the seats are arranged. What class is the classroom used for? If you're going to use an advanced course in a foreign language class or a lot of technical jargon, then the intelligibility of speech is critical. In this case, the microphone should be installed on the student's desk so that the speaker is less than 2 feet away from the microphone. Lecture classes do not need to interact with students frequently, so the speaker can be farther away from the microphone.
If students are going to open textbooks or handouts in class, they may block the microphone if they don't pay attention, which can lead to a loss of voice or noise. The slim, flexible goose-neck microphone solves this problem by raising the sensitive part of the microphone, avoiding noise and being closer to the speaker.
The most troublesome situation is that the layout of the classroom should be changed frequently and frequently. If the microphone can't be installed on the student's desk, it can only fall on the ceiling. When the students enter or leave the classroom, a lot of noise will be generated. Audio system design has produced defects that cannot be completely compensated for. In a classroom with a suspended microphone, the good audio quality of the classroom itself is especially important. If the audio quality of the room is poor or just average, then don't consider using a suspended microphone.
The case where the ceiling microphone is not suitable For aesthetic and safety reasons, the microphone is usually hung directly on the ceiling of the classroom and cannot be seen or touched. Of course, this is definitely the worst position for microphone installation. First of all, the distance of the ceiling microphone far exceeds the critical distance in most rooms, making the sound sound hollow and far away. Secondly, the ceiling is usually equipped with a changeover duct, which generates noise, and the ventilator also causes the ceiling to vibrate. The distance between the microphone and these noises is much greater than the distance from the students. Finally, students don't talk to the ceiling, and if they do, everyone speaks on the table or floor.
(2) Number of microphones turned on One factor that is often overlooked in audio system performance is the number of microphones that are turned on, referred to as NOM, which indicates the number of microphones that are turned on at any time. The sounds picked up by these microphones will be stored. On tape, it can be heard in other locations on the network. Only the microphones that are turned on affect the audio quality, and the microphone that is turned off with one switch does not work.
You might think that using multiple microphones to pick up the speaker's voice, the sound effect and volume must be better than a single microphone, and in fact, the idea is wrong, multiple microphones are even worse. Because each microphone picks up the background noise and the reflected sound of the room, it may not pick up the speaker's voice.
If only one person is speaking and using 4 microphones to pick up the sound, this may result in 90% of the picked up sound being noise and sound radiated from other locations. The background noise and reflected audio flowing into the audio system are turned on. A microphone is 4 times larger, and the speech content audio signal cannot be picked up because the other three microphones are usually far away from the speaker. This means that only the microphone closest to the speaker should be turned on. If you want to experience the experience of turning on 4 microphones yourself, you can install a tape recorder in the room where the speaker is speaking. First, turn on several microphones, then turn on only one microphone and compare the recordings separately. You can Feel that the quality of the audio picked up by turning off unnecessary microphones is very different.
In the classroom, how can I keep the unnecessary microphones off? There are three ways to do this: if necessary, arrange a specialist to operate the microphone; let the students operate the microphone themselves; use an automatic microphone mixer.
If a professional can operate the audio system in each class, the person is responsible for turning the microphone on or off when the student speaks. This is usually not a good idea, because even though it is the best operator, it is not able to respond to the speaker's speech in real time, and may lose something that has already been said. The student's question may not be a complete sentence. Another method is for students to operate their own microphones. This process requires the student to press the on/off button while speaking, so that the student can press the button to hear the speech. When students are speaking, if they can always remember to press a button, then this is indeed an effective method. However, this approach may vary due to different ages and different interest in the system. Some teachers feel that letting students operate such a switch system before speaking may create obstacles to classroom interaction, but some people prefer to be isolated from outside interference, preferring to manually operate while speaking.
The third solution to turn off unnecessary microphones is to use an automatic or "voice activated" microphone mixer. This is a microphone mixer that automatically turns each microphone on or off based on the position of the microphone sound. The basic automixer uses a simple "fixed limit" approach to decide when to activate the microphone. With this method, the volume of any microphone will exceed the minimum preset (called the limit) before the microphone is turned on and the speaker's voice is heard.
Proper adjustment of the fixed limit module is critical because the amount of background noise in each classroom changes from time to time, and the volume difference between the speeches of each person is also large. For example, if the limit is set very low, then the speaker with a small speech sound activates the microphone gently, then the system is too sensitive to background noise. Under this condition, the sound of the air conditioner is switched or the students are The sound inside the corridor activates the microphone. Conversely, if the limit is set high in order to prevent some sudden, erroneous activation, the voice of the speaker who speaks very little may not be heard.
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