Measure microphone level in WebRTC for iOS

I have a WebRTC iOS application. There I have AVAudioSession and RTCAudioSource. I need to detect when a microphone starts receiving loud sounds (like when a person starts speaking) similar to what hark does in the browser with AudioContext. How can I detect it or get something that resembles stream that can be measured like AVCaptureAudioChannel or AVCaptureAudioDataOutput?