Believe comparing of a confusion of voices: It is to show sound box answers put normal sound signal and signal of the noise when having signal (power) ratio. Also express with Db. For example, some tape recording believe comparing of a confusion of voices to be 50dB, output signal power to compare noise power big 50dB namely. Letter a confusion of voices is taller than numerical value, noise is less. The lowermost requirement that international Electrotechnical Committee compares to believing a confusion of voices is preamplifier is more than be equal to 63dB, class amplifier is more than after be equal to 86dB, amalgamative type amplifier is more than be equal to 63dB. Amalgamative type amplifier believes the optimal cost that a confusion of voices compares to should be more than 90dB.