What is the current state of the law in the United States on compelled evidence?

The American approach continues to perpetuate the narrow interpretation of incrimination originating in the plurality decision in Schmerber v. State of California, 382 U.S. 757 (1966), that only compelled evidence of a testimonial or communicative character is worthy of constitutional protection. In this sense then, coercion of an accused to produce voice to identify him or her is characterized not as a source of information against himself or herself but as a source of real or physical evidence.