Re: Ultrasonic Hearing in Music Recording & Reproduction

[kent walker <kent.walker@xxxxxxxxxxxxxx>]

>Date:    Wed, 23 Nov 2005 15:21:24 -0700
>From:    "Maher, Rob" <rmaher@xxxxxxxxxxxxxxx>
>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