Hi Fi is the abbreviation of high fidelity, translated as “high fidelity”, which is defined as a playback sound that is highly similar to the original sound. To evaluate whether a sound system or equipment meets the requirements of high fidelity, the subjective evaluation and objective index test should be combined, and the objective test index should be taken as the main basis.
Hi-Fi 是英语 High-Fidelity 的缩写，翻译为“高保真”，其定义是：与原来的声音高度相似的重放声音。评价一个音响系统或设备是否符合高保真要求，一般应采用主观听音评价和客观指标测试相结合的方式来进行，并以客观测试指标为主要依据。因为采用仪器测试设备的性能指标，能得到很直观的可供参考比较的定量结果，无疑是最科学而值得信赖的。那么什么样的音响器材的重放声音才是 Hi-Fi 呢？
Hi Fi is the abbreviation of high fidelity in English, translated as “high fidelity”, which is defined as playback sound which is highly similar to the original sound. To evaluate whether a sound system or equipment meets the requirements of high fidelity, the subjective evaluation and objective index test should be combined, and the objective test index should be taken as the main basis. Because it is the most scientific and reliable to use the instrument to test the performance index of the equipment, which can be used for reference and comparison. So what kind of audio equipment playback sound is hi fi?
迄今为止仍难以作出确切的结论。音响界的专业人士借助于各类仪器，通过各种手段，检测出各种指标来决定器材 Hi-Fi 的程度，而音响发烧友则往往通过自己的耳朵去判断器材是否达到心目中的 Hi-Fi。判别重放声音高保真程度的高低，不仅需要有性能优良的器材和软件，而且还要有良好的听音环境。因此，如何正确衡量音响器材的 Hi-Fi 程度，还存在着客观测试和主观评价的差别。
So far, it is still difficult to draw a definite conclusion. With the help of various instruments and various means, professionals in the audio industry can detect various indicators to determine the level of hi fi, while audio enthusiasts often use their ears to judge whether the equipment reaches the hi fi level in their mind. To judge the high fidelity level of playback sound, not only the equipment and software with good performance, but also a good listening environment are needed. Therefore, how to correctly measure the hi fi level of audio equipment, there are still differences between objective test and subjective evaluation.
Hi-Fi=高保真，发烧友口中的 Hi-Fi 系统一般指技术指标较高音响器材。Hi-Fi 上无止境。
Hi Fi = high fidelity, hi fi system in the mouth of enthusiasts generally refers to high-tech audio equipment. There’s no end to hi fi.
Hi Fi audio system can be divided into one-piece, suit type and combined type.
The integrated sound system is to assemble all kinds of functional equipment and loudspeakers in a case, which can not be disassembled at will. Such machines are generally low-grade popular machines.
The packaged sound system is designed by the manufacturer, which can be disassembled from each unit by matching various equipment lists.
Sound combination is to choose various types of equipment according to one’s hobbies and carry out free combination.
In the world of direct current (DC), the effect of objects on current is called resistance, but in the field of alternating current (AC), in addition to resistance, capacitance and inductance will also hinder the flow of current. This effect is called reactance. What we call impedance in daily life is the vector sum of resistance and reactance.
指向耳机输入 1 毫瓦的功率时耳机所能发出的声压级（声压的单位是分贝，声压越大音量越大），所以一般灵敏度越高、阻抗越小，耳机越容易出声、越容易驱动。
The sound pressure level (the unit of sound pressure is decibels, the higher the sound pressure, the greater the volume). Therefore, the higher the sensitivity and the smaller the impedance, the easier the earphone will sound and drive.
The sensitivity value corresponding to the frequency is the frequency response, and the image drawn is the frequency response curve. The range that human hearing can reach is about 20hz-20000hz. Nowadays, the mature earphone technology has reached this requirement.
大多数耳机线都以铜为原料，一般的纯度(一般用几 N 表示，比如 4N、6N……）越高导电性越好，信号失真越小，常见的有：
Most of the earphone cables are made of copper, with a general purity (usually expressed in several n, such as 4N, 6N…) The higher the conductivity, the smaller the signal distortion
TPC (electrolytic copper): 99.5% purity
OFC (oxygen free copper): purity 99.995%
Lc-ofc (linear crystalline oxygen free copper or crystalline oxygen free copper): the purity is above 99.995%
OCC（单晶无氧铜）：纯度最高，在 99.996%以上，又分为 PC-OCC 和 UP-OCC
OCC (single crystal oxygen free copper): the purity is the highest, more than 99.996%. It can be divided into pc-occ and up-occ
1、声底纯净，无任何令人不悦的“嘶”、“翁”、“哄”声。 2、平衡感好，音色不过冷或者过暖，高中低频能量分布均匀，频段间的融合自然滑顺 3、高频延伸良好，细腻而柔顺。 4、低频响应佳，干净饱满，富有弹性和力度，无任何肥大的感觉。 5、中频失真极小，饱满而温暖，人声亲切自然，有厚度，不夸张。 6、解析力好，细节丰富，微小的信号也能很好的重放。 7、有良好的声场刻画能力，声场开阔，乐器定位准确而稳定，声场中有足够的信息量，没有空洞的感觉。 8、动态没有明显的压缩，具有较好的速度感，大音量下不失真或失真很小。
1. The sound is pure, without any unpleasant “hiss”, “Weng” and “coax”. 2. Good sense of balance, the timbre is not cold or too warm, the energy distribution of high, middle and low frequencies is uniform, and the fusion between frequency bands is natural and smooth. 3. High frequency extension is good, delicate and flexible. 4. Good low frequency response, clean and full, full of elasticity and strength, without any feeling of hypertrophy. 5. The distortion of medium frequency is very small, full and warm, and the voice is friendly and natural, with thickness and no exaggeration. 6. Good resolution, rich details, and good playback of small signals. 7. Good sound field description ability, wide sound field, accurate and stable instrument positioning, enough information in the sound field, no empty feeling. 8. There is no obvious compression in the dynamic state, and it has a good sense of speed. There is no distortion or little distortion under high volume.
Sound quality evaluation
Range: the range between the highest and lowest pitch of an instrument or human voice
Timbre: also known as timbre, one of the basic attributes of sound, such as Erhu and pipa, are different timbres
Distortion: the output of the equipment cannot completely reproduce its input, resulting in waveform distortion or increase or decrease of signal components.
Dynamic: the ratio of maximum information to minimum information allowed to be recorded
Transient response: the ability of equipment to follow the sudden signal in music. The equipment with good transient response should respond immediately as soon as the signal comes to an end and stop abruptly as soon as the signal stops. (typical instrument: Piano)
Signal to noise ratio (SNR): also known as signal-to-noise ratio (SNR), the contrast between useful components of signal and noise is often expressed in decibels. The higher the signal-to-noise ratio of the device, the less noise it produces.
Air sense: an acoustic term used to indicate the ethereal and open treble, or the space between instruments in the sound field. High frequency performance is good, as if the ice water is general ethereal, as if there is air around, the feeling of emptiness and remoteness. At this time, the high frequency response can be extended to 15 khz-20 kHz.
低频延伸：指音响器材所能重放的最低频率。系用于测定在重放低音时音响系统或音箱所能延伸到什么程度的尺度。比方说，小型超低音音箱的低频延伸可以到 40hz，而大型超低音音箱则延伸到 16hz。
Low frequency extension: refers to the lowest frequency that sound equipment can play back. It is used to determine the extent to which a sound system or speaker can extend when playing bass. For example, the low frequency of a small subwoofer can reach 40 Hz, while that of a large subwoofer can reach 16 Hz.
They are mainly dynamic and electrostatic earphones.
Mainly home, portable, monitor, mix and binaural recording
According to the degree of openness
It is mainly open, semi open and closed (closed).
（1）开放式：一般听感自然，佩带舒适，常见于家用欣赏的 HIFI 耳机，声音可以泄露、反之同样也可以听到外界的声音，耳机对耳朵的压迫较小。
(1) Open style: Generally speaking, it has a natural sense of hearing and comfortable to wear. The hifi earphone, which is commonly used at home, can leak the sound, otherwise, it can also hear the external voice. The earphone has less pressure on the ear.
(2) Semi open: there are no strict regulations, and the sound can only be in and out, and the corresponding adjustment can be made according to the needs.
(3) Closed type: the earmuff has great pressure on the ear to prevent the sound from coming in and out, and the sound is correctly positioned. This kind of earphone is more common in professional monitoring field. However, this kind of earphone has a disadvantage that the low tone is seriously stained. W100 is an obvious example.