What are high-fidelity headphones

The main performance of the International Electrotechnical Commission IEC581-10 standard high-fidelity headphones is:

The frequency response is not less than 50Hz to 12500Hz; the allowable error of typical frequency response is ± 3dB;

The frequency response curve of two headphones (such as stereo) corresponds to the difference between the average sound pressure level of the bandwidth of each octave (its center frequency is in the range of 250 ~~ 8000Hz);

In the range of 100Hz-5000Hz, when the sound pressure level is 94dB (based on 20uPa), the harmonic distortion does not exceed 1%, and it does not exceed 3% at 100dB;