Subject: Re: A piano is a piano is... From: "Julius O. Smith III" <jos(at)ccrma.stanford.edu> Date: Thu, 15 Oct 1998 11:17:30 -0700> > If one is going to challenge, from an ethnomusicological point of > > view, the idea that an acoustic piano, as opposed to an electronic > > piano, is the "real" piano > > ... I suppose the main > issue is, how significant is the difference, to the human mind, of > various sounds of the piano-type. Another factor applicable when hearing a known recorded sound through a "poor medium", such as a small radio, is "known transformation compensation": we tend to "hear through" familiar transformations (such as "weak bass") and reconstruct the sound internally to some extent from memory. This effect is also active when hearing sounds in reverberant environments. We not only build a neural recognition apparatus for familiar sounds, but we also learn to partially compensate for systematic distortions that we are able to hear applied to many sounds. As everyone knows, various interesting auditory and optical illusions are based on this sort of "reconstruction in the mind" based on partial stimuli. Thus, the question "What sounds real?" is tied not only to the listener's entire life history of hearing examples of a particular sound source, but also to a lifetime of hearing how sounds can be modified in predictable ways by reverberant environments, narrowband media, and the like. Each individual will have a somewhat different "threshold of recognition" for various stimuli and distortion combinations. As a result of these considerations, it would seem the safest things to measure are simple JNDs. However, it would be great if we could also define "quality equivalence classes". At CCRMA, we often like to say that our synthesis models are "musically equivalent" to the original recording, and leave it at that. (As perhaps in Jim Beauchamp's example, often the most salient difference is that the noise is removed.) We generally try only to verify that the distortions caused by our synthesis techniques do not detract from the musicality or recognizability of the instrument tone, in the opinion of most listeners. The difference is often analogous to the difference between computer graphics and film recordings: those dinosaurs look very real, but suspiciously perfect and a little too "glossy". As audio coding converges more and more toward synthesis technology, "perceptual distortion measures" will become more and more a matter of opinion. Ultimately, we may have rely more and more on "critics" such as we now have for movies and restaurants. Julius Smith CCRMA, Stanford McGill is running a new version of LISTSERV (1.8d on Windows NT). Information is available on the WEB at http://www.mcgill.ca/cc/listserv