Hi,
The circuit also functions as a strange bandstop filter, where frequencies under around 105Hz get amplified, and frequencies above 1kHz get passed without too much attenuation, but frequencies within a certain bandwidth centered around 142Hz get cut quite a bit. So it's like a low pass filter and a bandstop filter. It may also be that it was made to work as a low pass filter with a very sharp cutoff.
That is of course assuming that the input signal has at least some dc bias voltage as well as the ac signal.