You want to hear someone really seamless, check out Rick Margitza. When I listen to his recordings i almost don't recognize that he's gone off the horn. The altissimo notes have the same quality as the rest of his tone. Not muffled or sounding like bugle calls.I was very impressed by his ability to work seamlessly in and out of altissimo when I saw him live. It actually shocked me a bit to hear the video clip of Giant Steps, which although impressive, was a bit grating.