How can I synchronize animation with audio source?

There are a lot of audioclip, so I can’t make specific animation for all of them. In the audio clip there are silent parts, where the person isn’t talking. I only want to play the animation when he is speaking, and not when he is silent. How can I solve this problem?

Look into AudioClip.GetData. You can find the amplitude of the sound at a given point and trigger your “silent” animation if the level is below a certain point. You will probably need to average many samples to stop spurious triggers.
DC

AudioSource.isPlaying
Check if audio is playing after you play it, if its not then it ended, so you can transition your animation to another.

AudioSource.isPlaying
Check the link for Unity Docs Reference.