A circuit for automatically discriminating audio intermediate frequencies
of a received television signal that has a simple, compact and inexpensive
circuit structure and can operate stably. The circuit comprises a high
pass filter circuit for eliminating a synchronizing signal from an output
of a video intermediate frequency detector; a synchronizing signal
separation circuit for separating a synchronizing signal from the output
of the video intermediate frequency detector; a waveform shaping circuit
for shaping a waveform of an output signal of the high pass filter
circuit; a counter for counting predetermined clock pulses; a counter
controlling circuit, which, triggered by the separated synchronizing
signal, (i) causes the counter to count the number of the clock pulses
that are contained during a period of time that is defined based on the
output of the waveform shaping circuit, and (ii) causes the counter to
output a counted value; and a discrimination signal output circuit for
discriminating a range, within which the counted value falls, from a
plurality of ranges, and outputting a discrimination signal according to
the result of the discrimination. The plurality of ranges are partitioned
corresponding to audio intermediate frequencies.