Machine for testing hearing level - has vocal and tonal circuits attenuating and filtering single frequency

摘要

The tonal circuit comprises pulses at stabilised frequency passing through a scaling-down circuit operating in cascade. Low pass filters are used, together with potentiometers, as a means of selecting the tones which are derived from the single input frequency of 48 kHz. The vocal circuit comprises a tape recorder (20), its output fed into a bank of six pass band filters (701 to 706) having a band width of one octave and scaled from 0.125 to 8 kHz. The filters are connected to logarithmic potentiometers (711 to 716) having linear displacement cursors. Their output through resistances (721 to 726) through a mixer amplifier (30) and an aperiodic attenuator (40) feeding a loudspeaker (50).