Manhattan School of Music professor and Skilled double bass participant Timothy Cobb training a bass lesson from the late 2000s. His bass contains a very low C extension using a metallic "equipment" with buttons for taking part in the pitches around the extension. This article has various concerns. Please assistance https://mooc.elte.hu/eportfolios/1694639/Home/The_Foremost_Article_to_Mp3Juice_Popular_Music_Downloader