Reading 14V PWM signal on Attiny85
First of all, use a voltage divider to reduce the voltage to ATTINY supply voltage level, then use an RC filter to filter the noise coming from the signal.
In this you have two options, if noise is low then use a very low-value capacitor and if noise is high and contains voltage spikes then use a high-value capacitor.
In both, cases your cutoff frequency should be at least 100 times the signal frequency ie 12KHz or above to avoid signal distortion.