Is Shadowing Native English Speakers Always Useful?
One way to improve your English pronunciation is by listening carefully to native English speakers and trying to imitate the rhythm of their speech. This is particularly helpful for more advanced English learners and should be accompanied by pronunciation coaching and reading exercises. Especially, speakers of languages that use very different stress and intonation patterns than English such as Asian languages can benefit from this. Less advanced students might not benefit as much from this technique. The pitfalls might be too high due to the phenomenon that we hear new languages not the way native speakers or very proficient speakers hear them but through the filter of our native language(s), or as the author of the article puts it: "The sounds that you hear go into your brain … and your brain interprets them or filters them through the sound system of your own language, and what your brain ends up understanding is not everything – it's not what the speaker intended…"
Therefore, many pronunciation exercises based on listening can lead to misunderstandings that may manifest themselves as fossilized errors later on. This is one of the reasons why I am not a fan of language cds for beginners. The following article addresses this problem very well and provides English learners with a number of useful tips here.