Subject: Re: Ultrasonic Hearing in Music Recording & Reproduction From: kent walker <kent.walker(at)mail.mcgill.ca> Date: Thu, 24 Nov 2005 02:29:33 -0500>Date: Wed, 23 Nov 2005 15:21:24 -0700 >From: "Maher, Rob" <rmaher(at)ECE.MONTANA.EDU> >Subject: ultrasonic hearing via bone conduction > >I recently received a query from a colleague about bone-conducted ultrasonic >hearing in humans. I also found a prior thread from a couple years ago >about ultrasonic perception here in the AUDITORY list. Based on the >published literature it seems clear that humans can get a hearing sensation >from ultrasonic vibrations coupled to bone. > >Anyone able to share their experience working with this phenomenon? Any >commercial hearing aids in this realm? > >It is also interesting that some audio equipment manufacturers are starting >to spec their loudspeakers into the ultrasonic range based on these >findings. > >Thank you, >Rob Maher> Dear Rob, I am not certain of your background or particular area of interest, however, please note that within the domain of sound recording this is a relatively "hot topic" fraught with debate - and quite honestly lots of BS. Does music contain ultrasonic information? James Boyk has shown that there is such content (http://www.cco.caltech.edu/~boyk/spectra/spectra.htm). Does current recording practice encode such frequencies? Well it depends on the microphones and the music, but mostly not. First of all, most of the microphones that engineers love and cherish are large diaphragms that "do not go up there". Secondly, lots of the processing gear that is currently in use "does not go up there", particularly digital equipment, although this is changing. And of course, the large majority of people are listening on reproduction systems, and using media, which "do not go up there". That said, there are a few famous engineers and designers who claim that this content is important. One paper that is cited add nauseum in the "for high-resolution" literature as a scientific justification is: http://jn.physiology.org/cgi/content/abstract/83/6/3548 I have not seen these results repeated (help list!). If these results are accurate, one hypothesis which has often been given is the possible presence of non-linear distortions, in other words, that subjects brains displayed the "pleasant response" to ultra-sound in the Gamelan recordings because of distortion in the recording and play-back systems. I personally am reserving judgment until I see much more data, however, either way it may not matter much. There are other possible benefits to increased bandwidth in recording and reproduction systems such as improved phase response, and improved spatial imaging. Are they significant to the average listener? Seems doubtful, but you never know! Many people think this is an area worth investigation. regards, -- Kent Walker Ph.D. Candidate McGill University Schulich School of Music Sound Recording Program Instructor MUSR 300D