Does the acoustic waveform mirror the voice?

Over recent decades, much effort has been invested in the search for acoustic correlates of vocal function and dysfunction. The convenience of non-invasive voice measurements has been a major incentive for this effort. The acoustic signal is a rich but also very diversified source of information. Computer literacy and technical curiosity in the voice care and voice performance communities are now higher than ever, and tools for voice analysis are proliferating. On such a busy scene, a review may be useful of some basic principles for what we can and cannot hope to determine from non-invasive acoustic analysis. One way of doing this is to consider communication by voice as though it were engineered, with layered protocols. This results in a scheme for systematizing the many sources of variation that are present in the acoustic signal, that can complement other strategies for extracting information.