1, concept,
PCM(Pulse Code Modulation) audio coding format is also known as Pulse Code Modulation. It is to turn analog signals such as sound into symbolic pulse columns, and then record storage.
2, the principle of
A time-continuous analog signal is converted into time-discrete digital signal, which is transmitted in the channel. Pulse code modulation is the analog
The process of sampling signals and quantizing the amplitude of the sample values.
sampling
It is to carry on periodic scan to analog signal, change time continuous signal into time discrete signal. The analog signal shall also be included after sampling
All the information in the original signal, that is, the original analog signal can be restored without distortion. The lower limit of its sampling rate is determined by the sampling theorem. In this experiment, the sampling speed
Rate with 8 kbit/s.
quantitative
It is to discretize the amplitude of the instantaneous value obtained by sampling, that is, to express the instantaneous sampling value with the closest level value of a set of specified levels. a
After sampling quantization of the analog signal, the quantized pulse amplitude modulation signal is obtained, which has only a finite number of values.
coding
It is a set of binary code to represent each quantized value with a fixed level. However, in fact quantization is completed at the same time in the process of coding, so coding
The process is also called A modulus/number transformation and can be denoted as A/D.
3, the characteristics
PCM signals do not undergo any coding and compression (lossless compression). Compared with analog signal, it is less susceptible to transmission system clutter distortion. Wide dynamic range, good sound quality can be obtained.
Under The Windows platform, WAV based on PCM coding is the best supported audio format, all audio software can perfectly support, because of its high sound quality requirements, WAV is also the preferred format for music editing and creation, suitable for saving music materials. Therefore, THE PCM encoded WAV serves as an intermediary format that is often used in the interconversion of other encodings, such as MP3 to WMA.
storage
Mono files, sampling data in chronological order in order to store. (Its basic organizational unit is BYTE(8 bits) or WORD(16 bits)).
Two – channel files, sampling data in chronological order interlaced storage. As shown in the figure:
Each sample value of the PCM is contained in an integer I whose length is the minimum number of bytes required to hold the specified sample length. The low significant bytes are first stored, the bits representing the sample magnitude are placed in the high significant bits of I, and the remaining position is 0.
Refer to the article: blog.csdn.net/ownWell/art…