I believe you must have a big audio format, but have you learned its storage principle? If you are an expert in this area, I can only use the "class door ax" to describe what I have made now. I wrote this article for friends who don't know much about this, of course, not every good programmer is Mr. Know-all, so I often cause some misunderstandings when I am in audio this. This is also the original intention I wrote this article. Of course, I don't dare to say that experts, the wrong leaks are inevitable, if there is discovery, please advise, listen in the earthen!
It is well known that the sound is an energy wave, so there is also a feature of frequency and amplitude. The human ear can hear the sound is due to the vibration of the air generates resonance. The frequency of vibration is the frequency of the acoustic wave. The acceptance ability of the general population is 20Hz to 20000 Hz, which is lower than this flooding, which is higher than this extensive is called ultrasonic wave. From music, the frequency of different tones is different, such as do, RE, MI is three different frequencies. Then, the sound of different musical instruments is like the same tone is the same, but we can hear their differences. What is going on? This is the difference in tone, in fact, the difference between the sound of the sound of different musical instruments is not on the frequency but in the waveform.
Any true voice, even if it is just a sound of 蛐蛐, almost like the product of a symphony band, they seem to be the results of many instruments. Simply put, the general voice is equivalent to a large number of tuning sounds, which are composite waves. In fact, the violin, the cello, the black tube, the organ, the flute, the trumpet, the sound drum, the cymbal,, sand hammer, etc., is because of their different compositions of their composite waves. For example, human ECG and EEG are completely different waveforms, two sets of acoustic waves, the same frequency is the same, but in the shape of a cycle, people's ear audible sound will have a big difference.
The principle of speaker in the speaker is actually very simple, that is, through electromagnetic induction phenomena, the changed current is converted to a pot of vibration, thereby generating air vibration, and then people will hear the sound. Therefore, as long as there is a frequency within the range of the human ear to accept and a powerful current input the speaker, the human ear can get a sound pressure within a sufficiently near voice field, which is heard. Of course, in the multimedia active speakers except for the speaker, there are devices such as op amp (current amplifiers) and power amplifiers (power amplifiers), which are generally enlarged to enlarge the input current and power to the speaker can emit a sound. The sound card on the computer is to transmit the digital audio data from the CPU to buffer, processing, shunt, conversion, etc., and transmit the current carries the analog signal to the speaker through the audio interface, so that it sounds.
Now that the principle of electroacoustic, Edison invention is using this principle, and the curve of the sound waves on the record, and then use the singing needle to create vibration along the wave line, and use the current to enlarge the sound. . This is actually the simulation signal that is now used to represent the sound wave with a smooth curve, but the computer data can only be represented by 1 and 0, then how should the computer indicate sound waves? Below we will introduce a concept "sampling rate".
The number of points to the sound wave is called a sample rate within a second. It is assumed that the sound wave is a SiN curve that is taken along the X positive direction, then we can take a value of different Y directions along the X direction, which is called a sample value. Of course, the number of computers can be limited, we cannot sampling the curve in an unlimited amount of increment in the X direction, so we can only sample the waves in the fixed interval. The sampling process is actually in the extraction of the amplitude value of a certain point in the sound wave, it is clear that the more extractions in a second, the more amplitude is obtained, and the description of the waveform is more accurate. The highest frequency of the human ear can feel 20kHz, but the voice of the human ear will not be very sensitive, so at least 2 points in the vibration cycle, it can basically meet the auditory requirements, that is At least 40K sample samples per second, expressed 40 kHz, this 40kHz is the sampling rate. Now we can use the numbers to indicate sound waves, but this is enough, we must also use a fixed size value to represent the quantization value of each sampling point, this quantization value is called "bit rate", which is usually said " Bit rate. In order to facilitate computer representation, the bit rate is set to 2 integers, so our common CD is sampled at 16bit sampling points per point, and the amplitude of the amplitude can be said to be 2, that is, -32768 to 32767 . Of course, the higher the sampling rate, the more the waveform is reproduced, the more accurate sound, but it is not the bit rate, the more you can show greater volume? In fact, it is not the case, such as a value of 16 bits, and 8-bit maximum performance 255, but when the computer is converted, it will make a mapping, such as 16-bit value 32767 to 8-bit conversion It will be reduced to 255, which is actually exactly the same, but the higher the bit rate, the more dynamic details are more dynamic.
Now you may notice a little, common sampling rate is 48000, 44100, 22050, 11025, etc. Why isn't it 50000, 10000? The extreme frequency of the human ear is 20000Hz, and the sampling rate is more than twice the frequency, and the human ear can distinguish between the sound, so it corresponds to the maximum accepted frequency of the human vectors, but also for the machine computer convenience, set The standard sample rate of the CD is 44100, which is lower than his sampling rate calculated according to his division, and is greater than the integration of 48000.
Now let's take a look at the memory of the music CD. The full name of the CD is Compact Disk, which is a laser storage medium that stores data with a metal film covered on a circular plastic sheet. The data on the CD is stored in a digital manner, that is, 0, 1 data, each bit is a point on the metal film. These points are arranged by the inner ring to the outer ring in the order of concentric circles, and the todged tabs 0 or 1. When the laser is irradiated on the disk, the convexus will have different reflections so that the data is read. The music CD is a paragraph tag according to the track, and the digital waveform data told above is on the disk. The audio CD format is a pure digital track, no verification, but the world is impossible to have a perfect disk, more or less physical damage, which leads to the loss of audio data. But in general, this is negligible, very small disk scratches for the damage of music data, even if the instrument is difficult, not to speak people, but the enthusiasts are endless to the perfect pursuit. Now there is a software that uses repeated reading and demand averages when it is grabbed, and the name of this software is called EAC.
