Echo exists in traditional PSTN connections as well as VoIP connections, but due to delay that is inherent in VoIP, it can become much more noticeable. The echo that one experiences is probably the result of the far end, where an impedance mismatch bounces signals back from where they came....
Nadine ($599) is a large-diaphragm condenser microphone specifically designed for use on upright basses, tuned to provide the most natural sound for acoustic bass in a live setting or in studio ensemble recordings. The low end is tuned to give a flat response at the mounting distance, and ...
As far as A/B/Xing, one has to achieve darn close to 100% and on the first attempt, if more than one attempt is made, then any/all previous attempts must be calculated into the result. Another irony (just to me) is that if it isn't 100% and it's that important and discernable...