The pitch problem is exacerbated by in ear monitors compared to over the ear cans because of what is called the occlusion effect. This shifts the balance of frequencies highly towards the low end and it messes with the psychoacoustics of our pitch control circuits in our brains. Occlusion effect doesn't really happen with cans because they don't seal the ear canal. They do block out room reverb as a feedback mechanism, but that can usually be corrected by adding in some reverb to the voice coming back into the cans. Occlusion effect cannot be passively controlled with IEMs. Some can train themselves to rewire their pitch control with IEMs, but it takes time and effort. Like I said I have Westone ES5 IEMs, but I do vocal tracking with a cheap set of Samson circumaural cans. The Westones are wrth 10x the Samson. Now, for tracking acoustic guitars and other mic'ed instruments, the Westone's rock because they let me hear what the MIC hears much better than the non isolating Samsons.

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