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]