Sensitivity  --  The minimum value of input signal that is required by an electronic unit, such as a tuner, to deliver a specified output signal level. The measure of a microphone's sensitivity is an indication of efficiency. A classical dynamic mike may have a sensitivity of 0.2 mV. A model giving 0.25 mV is considered sensitive and 0.1 mV is unsuitable for recording low frequencies. Condenser mikes always have a preamplifier in the mike casing otherwise their high impedance would not allow the signal to be transmitted along a cable. It is difficult to produce a very low noise preamp capable of receiving without overloading a signal given by a condenser mike placed in a strong acoustical field. For this reasonit is better to have special preamps for condenser mikes.