[Argus25]

I'd go for a simple circuit that uses a zero crossing detector and generate a narrow pulse. This tends to eliminate noise and amplitude components which are unimportant. If the signal is distorted it doesn't matter and it can also be filtered too. (On this topic I made a link to the processing of the signals from audio tape for early computers like the Sol-20, these do a terrific job of what amounts to zero crossing detection and due to an agc works over a large range of input signal levels, but I can't attach it on on my mobile device easily)

Once you have your narrow pulse it's dead easy to convert it to a DC voltage proportional to frequency. All you do is feed it to a transistor which resets (discharges) a capacitor voltage to zero over the time of the narrow pulse. Then you charge the capacitor with a constant current source.Then the peak of that climbing ramp signal is merely peak detected by a diode and filter cap with a parallel resistor and that is buffered at the + input of an op amp. It could for example be made to vary from 1 to 9v depending on what you want and your supply voltages. You get a nice stable DC level between updates , it's a simple sample hold. The technique was used in some early servo systems in VCR's and it works very well and is simple for a frequency to voltage converter, either for a meter or a servo system.