Introduction to Acoustics

778 Part E Music, Speech, Electroacoustics
Part E 18
to the side than can be achieved with the front speakers
(or stereo), exercising the full range of the ITD/IAD sensitivity
of the ear, and providing the option of a far more
immersive experience than can be attained with stereo.
18.7 Appraisal and Speculation
We have been witness, from the crude but noble origins
of sound reproduction, to an astonishing march of
progress that has, by degrees, rolled down the problems
and imperfections of sound reproduction, reaching
a notably high level of performance, when considered in
basic perceptual terms.
A cynic might note that, fifty years ago, children
played little yellow plastic 78 RPM 17.78 cm discs on
phonographs that had 12.7 cm loudspeakers, and now,
after fifty years of dramatic, hard-won progress, many
people play little 12.7 cm plastic (compact) discs on
boom boxes with 12.7 cm loudspeakers. Yes, the fidelity
is better, as is the playing time, but have we really come
that far?
The apparent answer from all the above is that
a high-quality system of modern vintage can now satisfy
a major percentage of the electroacoustic and spatial
requirements implied by the capabilities of the human
auditory system.
This does not mean that audio engineers call all just
pack up and go home just yet. Indeed, the quantities
of audio research papers and patents published each
year show no sign of abating, giving rise to the speculation
that further meaningful improvements may yet
be attained.
One can certainly wish for a few more channels,
to fill in the remaining gaps and perhaps even provide
explicit coverage above and below the listener. The issue
in that regard at this point is more of practicality than
of theory. There have been some experiments with the
addition of height or ceiling (voice of God) channels,
and the specifications for digital cinema systems allow
for the use of over a dozen channels.
One can also hope for enhanced ability to project
sound into a room, rather than having it just arrive from
the walls. That is another area of active investigation.
One approach, referred to as wave field synthesis [18.71]
References
18.1 N. Aujoulat: The Cave of Lascaux (Ministry of
Culture and Communication, Paris August 2005),
The 5.1 format with high-quality source material
provides the most accurate overall audio reproduction
of any widely used format to date, within either the
“here” or “there” reproduction paradigms.
has been to approximate a complete sound field by reproducing
the sound-pressure profile around a periphery,
and relying on the Huygens principle [18.72] to recreate
the complete interior sound field. This requires large
number of loudspeakers (192 in one experimental setup)
to avoid spatial aliasing effects.
The other well-known approach to generating interior
sounds is to use an ultrasonic audio projector, which
projects acoustic signals above the audio band which
heterodyne to produce audible sound which appears to
come from a remote location [18.73].
Another problem that has only partly been solved
is that of sweet-spot sensitivity. This has long been an
issue with cinema surround-sound systems, but is no
less challenging for automotive surround systems, where
there are often no centrally located seats and speaker
locations may be less than optimal. The issues go beyond
balanced sound to trying to provide a coherent,
immersive experience at all listening positions.
Indeed, each new venue for audio seems to come
with its own idiosyncratic problems, leading to active
investigation of how to make compelling presentations
for portable music players, cell phones, and interactive
media such as game consoles.
It is also expected that there will be continuing
refinement of binaural techniques for personal
listening.
Ultimately there may come a wholesale revolution
in audio techniques, perhaps with laser transducers
replacing loudspeakers and microphones, along with
holographic recording of entire sound fields. For personal
listening, your music player might interface
directly to your brain, bypassing the ear altogether, allowing
otherwise deaf people to hear, and getting rid of
that troublesome 3 kHz peak in the ear canal once and
for all.
It should make for some interesting vibes.
http://www.culture.gouv.fr/culture/arcnat/lascaux
/en/