The Sound Quality Standard

- Jul 26, 2018-

The so-called sound quality refers to the fidelity of the audio signal after transmission and processing. At present, the industry recognized sound quality standards are divided into 4 levels, namely the CD-DA quality of digital compact disc, its signal bandwidth is 10Hz~20kHz; FM broadcast FM quality, its signal bandwidth is 20Hz~15kHz; AM broadcast AM quality, its signal The bandwidth is 50Hz~7kHz; the voice quality of the phone has a signal bandwidth of 200Hz~3400Hz. It can be seen that the digital compact disc has the highest sound quality and the telephone has the lowest voice quality. In addition to the frequency range, other methods and indicators are often used to further describe the sound quality standards for different uses.

For analog audio, the more frequency components of the reproduced sound, the smaller the distortion and interference, the higher the sound fidelity, and the better the sound quality. For example, in communication science, the level of sound quality is measured by indicators such as distortion and signal-to-noise ratio in addition to the frequency range of the audio signal. For digital audio, the more components that reproduce the sound frequency are the smaller the bit error rate and the better the sound quality. Usually measured by the digital rate (or storage capacity), the higher the sampling frequency, the larger the number of quantization bits, the more the number of channels, the larger the storage capacity, of course, the fidelity is high and the sound quality is good.

The sound categories are different and the sound quality requirements are different. For example, the sound quality fidelity is mainly reflected in clear, undistorted, and reproduced flat sound images; the fidelity of the music is required to be high, and the spatial sound image is mainly embodied in multi-channel analog stereo surround sound, or virtual two-channel. 3D surround sound and other methods to reproduce all the sound images of the original sound source.

The use of audio signals is different, and the quality standards for compression are different. For example, the telephone quality audio signal adopts the ITU-TG711 standard, 8 kHz sampling, 8 bit quantization, and a code rate of 64 Kbps. The AM broadcast uses the ITU-TGĀ® 722 standard, 16 kHz sampling, 14-bit quantization, and a code rate of 224 Kbps. The high-fidelity stereo audio compression standard is jointly developed by ISO and ITU-T. The CD11172-3MPEG audio standard is 48kHz, 44.1kHz, 32kHz sampling, and the digital rate of each channel is 32Kbps~448Kbps, which is suitable for CD-DA discs.

 

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