6/1/16: Noisiest?

Based on my experience listening to PA systems, I would say the largest noise component would be power line frequency noise, coupled in through a dynamic mic. Otherwise, I don't mean to give you a cop-out answer, but unfortunately it is hard to say without specifics. In the best case, you can design a signal chain where the majority of the noise comes from the mic resistance and associated Johnson noise. The digital part of the signal chain isn't likely to contribute noise directly, unless the switching currents are coupled back to your audio signal via board layout. And I hope this webcast has given you the tools to analyze and optimize the analog portion of the signal chain for noise.