Launch Ableton Live. Open the project containing the audio track to which you want to add a wah effect. Click the track to select it.
Click the "Live Device Browser" icon. Open the "Audio Effects" section. Drag and drop the "Auto Filter" entry onto the track.
Click the "Bandpass" icon. Drag the yellow circle in the Auto Filter window to the left until the frequency readout displays "300 Hz."
Turn the "Amount" knob in the "LFO" section up to "30.0" and set the "Phase" knob to "0.00." Click the "Shape" drop-down menu and select the triangle icon. Turn the "Offset" knob to "180."
Click the music note icon next to the "Rate" knob, then click and drag the knob to change the speed of the wah effect. Start with a rate of "1/2," then try different rates until you get the desired wah sound. Tweak the other settings as desired to fine-tune the effect.