Precision Oscillator With 20ns Switching
Precision oscillator can be built using quartz crystal, but with proper component selection, you can also build one with RC (resistor and capacitor) circuit. Not only to build a tone/frequency decoder, 567 IC can be used to build such oscillator as well.
The good news is that you need only few components, and a VCO terminal to fine tune the frequency. Just make sure if the input of this pin (if used) is supplied with a stable voltage. Fast slew rate (20ns switching) is the bonus for using this 567 IC. The frequency formula for this circuit is f=1/(1.1xR1xC1). [Circuit’s schematic diagram source: Philips Semiconductors Datasheet]