HIFI sound on what mean?

HIFI sound on what mean?
http://www.siliconray.com/sense-g5-tube-solidstate-hifi-headphone-amplifier.html
Hi-Fi is the abbreviation of English High-Fidelity, literal translation for "High Fidelity" is, by definition, : and the voice of the original highly similar to the replay of sound. So what kind of audio equipment the replay of voice is Hi-Fi? So far is still hard to make the exact conclusion. Audio industry professionals with each kind of instrument, by any measure, detection of all kinds of the index to determine the extent of the equipment Hi-Fi, and audio fancier then often through their ears to judge whether the equipment to mind the Hi-Fi. Heavy pitch discrimination lifted the degree of fidelity, not only need to have good performance of the equipment and software, and have good listening environment. Therefore, how to measure the acoustic equipment Hi-Fi degree, there are objective and subjective evaluation, the difference between the test.
Hi-Fi = high fidelity, hair ?
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