The k of the mobile phone amplifier represents the size of the clarity, the larger the number in front of the K, the higher the clarity, on the contrary, the smaller the number in front of the K, the lower the clarity. K generally represents the gain, which is the amplification of the signal. K> 0 indicates that the signal is amplified, K=0 indicates that the signal is straight through, k< 0 indicates that the signal is attenuated and weakened. At low frequencies, K affects the steady-state performance of the system, and the higher k is, the better.