Introduction of FM transmitter
The FM transmitter is a personal micro-broadcasting station, which can convert the audio signals from various portable audio and video players such as Discman, MD, MP3 (including Apple iPod), mobile phones, and tablet computers (including iPad) into high-fidelity wireless The FM stereo signal is transmitted out, and the car or home radio is used as the receiving object, and you can enjoy stereo music, thus bringing the music to a "big shift". Expand the application function and application environment of these players in your hands.
Technical discussion, First of all, sound is a kind of vibration, and electric current drives the horn to vibrate to produce sound. The more the speaker vibrates like the original musical instrument, the better the sound quality. The method of recording the vibration directly is the analog recording method, which is similar to tapes and vinyl records. In theory, this kind of recording has the best sound quality. However, due to the poor anti-interference of this kind of media, it is also difficult to store, so in addition to the professional mastering method and the use of magnetic tape, other methods are eliminated.
The era of digital recording and preservation. Digitization, to put it simply, is to continuously record the sound intensity at consecutive points in time, turning it into a string of numbers, and then broadcast the sound when it is restored. This recording process is called "sampling".
In order to restore the original signal well, when the signal is digitized, it is required that the frequency of the sampling clock should be at least twice the highest frequency contained in the signal itself. This requirement is usually called the Shannon sampling theorem.
The human ear can hear the audio signal from 20HZ to 20KHZ. The frequency range of human speech is 300HZ to 3400HZ. Therefore, the human voice must be accurately restored. The sampling frequency must be at least 6800HZ. If you want to accurately restore all sounds, you need 40KHZ.
FM is a broadcasting modulation method. Its highest sampling frequency is 22khz, and each sampling point is represented by 8bit, which is 0-255, which means that it can only better restore the sound below 11khz. This is listening The reason why the treble part of the FM broadcast is greatly lost (6800HZ<11KHZ<40KHZ).
The ordinary CD is 16bit 44.1khz, so the sampling can cover the frequency range of all ears, and the sound intensity is represented by 0-65535, which is obviously much more delicate than FM.
The commonly available CDs are all in HDCD format, which can be close to the quality of 24bit 44khz, and the information content is 131072 times that of FM.
use
The most useful ones are the navigators. Portable navigators basically have the function of FM transmission. Relatively speaking, the functions of this function are more obvious and more applicable.
how to use
The first step: turn on the navigator to turn on the frequency band, and then adjust a radio frequency band that is not frequently used. (E.g. 80.00)
Step 2: Adjust the frequency band of the car's radio to the same 80.00.
Therefore, only the above two steps are required to transmit the sound of the navigator through the car's audio. (This kind of relative is only very practical for portable navigators)
Note: Choose an uncommon frequency band to avoid interference from radio channels.
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