Audio formats.
There are many types of voice file formats, as well as image file formats.
Since the digital audio files are easy to copy, the illegal copy and distribution of music files has become a problem these days.
As explained in what analog data is, the mechanism of digital audio files is that analog signals become digital data and are saved.
Explaining in detail the conversion method, to convert an analogue to digital waveform, it is necessary to perform a job called “sampling” that measures (record) the sound waveform at regular intervals, and is the sampling cycle. The sampling frequency is called (sampling frequency).
The sampling frequency represents the number of samples per second and is in Hz. In other words, it is a unit that expresses how many times the sound is measured and recorded per second, and the greater the value, the more faithful the original and greater sound becomes the quality of the sound. However, the amount of data will increase proportionally.
The sampling frequency of a typical music CD is 44.1 k Hz. However, even if the sampling frequency is increased, there are sounds and frequency bands that can not really be recorded, so some classical music enthusiasts love expensive analogue equipment.
In addition, it is not only the sampling frequency, which affects the quality of the sound, but also the “sampling bit” that indicates the strength (volume) of the sound (16 bits are 65,535, 24 bits are 16,777,215). (Express) and “Number of channels” (number of sound lines recorded as stereo, monaural and 5.1 channels) also have an effect. The higher the value, the greater the sound quality.
Another factor that greatly affects sound quality is the bit rate. The bit rate represents the amount of data to be recorded per second and the unit is “BPS”.
In other words, the higher the bit rate, the more information can be stored, which results in a higher sound quality. As will be described in detail below, in the MP3 file format, 128 K BPS is the minimum bit rate that can be heard.
However, there is “constant bit rate” and “variable bit rate” in the bit rate. The constant bit rate is the same bit rate that is fixed from the beginning to the end of the voice, and the variable bit rate increases or decreases the bit rate according to the amount of voice information.
In other words, the bit rate is high for clauses with multiple voices and the bit rate is low for simple low voice clauses. You can reduce the total size of the file by choosing a variable bit rate.
This is the information contained in the digitized data of analog audio signals.
However, digitized data can not be used as. Just converting this data into an arbitrary file format and saving them, it will be possible to use them with multimedia devices and application software that admit that format.
The storage format of said data
file format
Is named. A file format is a file format with an extension.
Then, to save the data in a file format, it is necessary to transform (encode: encoding) the data according to that format. (For coding, see What is a character code?)
A dedicated program is used to codify the data, but said coding program is
Codec (codec)
Is named. In other words, the gross data obtained by converting analog signals into digital data are processed by a codec to market them as a file format.
Therefore, there are many types of codecs and coding methods for each type of codec.
Most current codecs are programs that compress and encode data when creating a file and decompress (decompress) data by playing a file. In general terms, codecs are used to compress and decompress data. It refers to a compression method program of this type.
