Introduction of transistor sound, digital sound and electromagnetic interference sound
Transistor sound: Those who have heard of transistor amplifiers (discrete components) and those who have heard of integrated circuit amplifiers will definitely say that transistor amplifiers sound good, and those who have heard of vacuum tube amplifiers and transistor amplifiers will also say that vacuum tubes are good. In contrast, the sound of the transistor amplifier is hard, especially the high-frequency part of the sound is tingling and dry, especially the integrated circuit. However, in terms of technical indicators, integrated circuits are the best, transistors are the second, and vacuum tubes are the worst. Why is that? Mr. M. Otala, a world-renowned electroacoustic expert in Finland, conducted an in-depth study on this in the last century. The conclusion is that since transistors (including integrated circuits) are generally made to be directly coupled and exert a negative 40 to 60 dB in the circuit Feedback, so that the technical specifications of the amplifier are very good, and the amplifier with the original distortion of 10% is reduced to 0.1% at a time (in the case of negative feedback of -40dB). However, in this circuit, in order to make the amplifier work stably after adding deep negative feedback, a lot of "compensation" is needed, which in turn causes the amplifier to produce TIM (transient intermodulation distortion), and TIM makes people in There is a very uncomfortable feeling in the middle and high frequencies of the sound. This kind of sound is called "transistor sound". Since the amplification stages of the vacuum tube amplifier are very small, basically no deep loop negative feedback and no compensation are required. Therefore, there is no TIM. This is one of the important reasons for using a vacuum tube as an amplifier to make the sound quality pleasant and pleasant.
Digital sound: The signals that our human ear can hear are all analog signals. Before the digital audio recording format (CD) was invented in the 1980s, the records (LP) and magnetic tapes we heard were recorded with analog signals. of. After the appearance of CD digital recording format, because digital signals are convenient for storage, recording, and processing, more and more signals are recorded in digital formats, such as VCD, MP3, MD, and DVD. Although the digital format recording signal has many advantages, there is also a serious problem, that is, a program source that does not have an analog recording method in listening sense is natural and nice, and there is always a blunt feeling. This is because if the digital signal is recorded in an analog manner, this will inevitably result in a very large amount of data. Therefore, the digital format for the analog signal must be compressed. The compression is based on the Nyquist sampling law. Ness's law, in principle, as long as two samples are taken within a signal period, the original signal can be restored. If the signals are all sine or square waves, in principle, they can be completely recovered. However, because the music signal has a lot of harmonics, so much information (such as the harmonics of the violin and piano) is lost in the high-frequency part; the more the sampling frequency Low, the more lost the signal, the heavier the digital sound (more rigid), which is the reason why MP3 does not have a good CD (also the reason why CD does not have a good SACD). The reasons for the generation of digital sound are as follows. One is that the digital signals are all square wave signals, and the analog signals recovered by D / A are all combined with square waves. According to the Fourier transform, the square wave signals are It is composed of fundamental wave and very rich high-order harmonics. Although there are filter circuits after D / A, the high-order harmonics are always difficult to filter 100%; the second is that there is still a kind of "digital signal conversion" "Time base error (jitter)", "time base error" will deteriorate the sound quality; third, there is a unique "intermodulation distortion" phenomenon in digital signals, which will produce quantization noise; fourth, digital signals are reading There is also a "bit error" problem in fetching and storage. The result of the "bit error" is signal distortion. Therefore, these four reasons make us feel that kind of blunt "digital sound" in the sense of hearing.
Electromagnetic interference sound: In Hi-Fi amplifiers, the power supply is very particular, and experienced designers know that the power supply is very important to make the amplifier good. There are two kinds of power supply, one is the use of traditional transformer structure, the other is the use of switching power supply. Switching power supply amplifiers are not used in traditional amplifiers. The main reason is that the switching power supply has serious electromagnetic interference, which deteriorates the sound quality, that is, the sound has a burr feeling. In addition, all data communication in the computer host chassis is performed in digital format, and the computer's sound card is placed in the chassis and powered by a switching power supply, and its electromagnetic interference can be imagined. This kind of sound deterioration caused by electromagnetic interference is called electromagnetic interference sound.
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