The audio frontier is all abuzz these days with the
pleasure possible though HDMI, USB, FireWire® and Ethernet
connections. However, these current generation digital technologies
are only part of the story, just as the challenge of designing,
manufacturing and choosing the best analog interconnects and
speaker cables is as important as ever. The S/P-DIF (Sony Philips
Digital InterFace), which arrived in 1983 along with the CD, is
still very much a part of our world today. S/P-DIF is transmitted
through Digital Coax and Toslink fiber optics (EIA-J), making them
still some of the most important cables in electronic
entertainment.
While, thanks to HDMI, Toslink is not so often used
to connect a DVD player to an A/V receiver, Toslink connectors are
common on cable-boxes, TV sets, subwoofers, all sorts of products.
And now, the 3.5mm Mini Optical connector, also somewhat
incorrectly known as Mini-Toslink, is everywhere ... from the 3.5mm
dual-purpose headphone jack on a Mac laptop, to inputs on some of
the finest portables.
For these many reasons, AudioQuest has refined and
renewed our line of serious high performance OptiLink cables. All
models and all lengths are now available Toslink to Toslink and
Toslink to 3.5mm Mini Optical.
When the question is "how can a fiber-optic cable
change the sound?" ... the answer is easier to explain than for
almost any other type of cable. If the light source were a coherent
laser, firing into a vacuum, all the light would stay straight,
arriving at its destination at the same time. Even if the LED light
source in a Toslink system were coherent, the light entering a
fiber-optic cable is scattered and dispersed by imperfections and
impurities in the fiber. This can be measured as a loss of
amplitude ... but amplitude is not the problem, a 50% true loss
would have no effect on sound quality.
The problem is that the dispersed light does get
through the cable, but only after it has taken a longer path, like
a pool ball bouncing off the side-rails, causing it to arrive
later. This delayed part of the signal prevents the computer
charged with decoding this information from being able to decode
properly, or even at all. The inability to decode shows first at
higher frequencies (not audio frequencies, this is a mono stream of
digital audio information), so reduced bandwidth is a measurable
signature of light being dispersed by a fiber. The punch line: The
less dispersion in the fiber, the less distortion in the final
analog audio signal presented to our ears.
There is another serious dispersal mechanism in the
Toslink system. The fiber is a relatively huge 1.0mm in diameter,
and the LED light source is also relatively large, spraying light
into the fiber at many different angles. Even if the fiber were
absolutely perfect, the signal would be spread across time because
light rays entering at different angles take different length paths
and arrives with different amounts of delay.
The almost complete solution to this problem is to
use hundreds of much smaller fibers in a 1.0mm bundle. Because each
fiber is limited as to what angle of input can enter the fiber,
there is far less variety, and far less dispersion over time. This
narrow-aperture effect is similar to how a pin-hole camera can take
a picture without a lens ... by letting in light at only a very
limited range of angles, a picture can be taken, whereas removing
the lens from a wider aperture would make photography impossible.
Less light gets through a multi-fiber cable, but the light that
does get into the fibers comes out within in a much smaller
time-envelope.
So there is one problem, the dispersion of light
across time ... and two avenues towards a better result: less
dispersion in the fiber (better polymers and ultimately quartz),
and less dispersion by filtering the input angle. How simple is
that! Listen and enjoy.
