indicated in waveform b most of the harmonic or overtone energy has been removed the energy retained is mainly the fundamental pitch frequency of the voiced sounds received by the transducer there remains however some energy of the second and third harmonics and the amplitude of the waveform is not uniform consequently the filtered signal now goes through an automatic level control processing in particular the output of the audioamplifier 26 which is a negative feedback amplifier is fed to audioamplifier 28 from there the signal is peak detected by detector 30 and fed via automatic level control amplifier 32 to the input of the automatic level controller 34 whose output generates a negative feedback signal controlling the level of the signal passed by audio amplifier 26 as can be seen in waveform c solid line of fig2 the pitch frequency information is retained except that the intensity of level has been controlled for a constant peak to peak value it should be noted that the automatic control time constant that is the time the automatic level control circuit takes to correct a level change is approximately 50 msec this time constant is chosen to allow for the lowest male pitch of approximately 60 to 70 hz and yet retain 34 fast 34 alc response further filtering is performed by the comparator 36 having a signal input connected to the output of audio amplifier 28 and a reference input connected through a resistive divider network rr to the comparator output the comparator is designed such that all vestigal harmonic energy of.