I have to disagree with the choice of Listen to the Music as an example of synth. In fact if you watch this video, you wont see a synth. I would say flanger on the guitar, yes but not synth. Now maybe you meant some of the tracks from the Michael McDonald era, like What a Fool Believes...you know when the Doobies went soft lol. :D But I still like the Doobies and they enjoy airplay still ( even in the grocery store) LOL.