FIFTY million homes worldwide now own huge TV sets that can thump out booming
cinema-like sound from surround-sound loudspeakers. But because the racket
annoys the neighbours, such TV sets can rarely be used to their full
potential.
To the rescue comes the former prime minister of Australia, Paul Keating. The
company in which he has a multimillion-dollar share, Lake Technology of Sydney,
has licensed an idea to surround-sound pioneer Dolby Laboratories which can make
standard stereo headphones sound as good as a room with many loudspeakers.
Dolby鈥檚 surround-sound systems use at least five speakers, often with a
鈥渨oofer鈥� adding heavy bass. Both the listener鈥檚 ears hear sound from all the
speakers, and reflected from the walls. But if the sound is fed direct to
headphones, the left ear hears only the sound intended for the left speakers and
the right ear hears only that for the right speakers, giving an effect just like
standard stereo.
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If, on the other hand, the original sound was for headphone-only
listening鈥攑erhaps by recording using microphones stuck inside the ears of
a dummy head so they are the right distance apart鈥攊t sounds realistic on
headphones but unnatural through speakers.
In the 1990s, Lake Technology patented a signal processor which digitally
modifies the frequency content of an audio signal, achieving a similar effect to
an analogue filter. Dolby bought a licence to use the patent, measured the way
the left and right ears hear sound waves from speakers around a room, and
programmed the Lake filter to add a matching effect to signals fed direct to
each ear. The effect involves adding artificial 鈥渞eflections鈥� to the signal to
give the listener the feeling of being in a bigger space.
Singapore Airlines and Qantas are already using the system to process their
inflight audio. Because passengers only listen on headphones, it does not matter
that the sound would seem wrong if it were played on speakers. Dolby has now
licensed electronics companies Motorola, Texas Instruments, Zoran, Analog
Devices, Sharp and Sanyo to make sound-processing chips that filter recordings
intended for listening though loudspeakers to make them sound natural on
headphones.
A black box sits between an amplifier and stereo headphones, continually
adding open-room reflection effects to each of the five speaker channels, and
feeding the processed sound to the left and right ears. The listener hears sound
apparently coming from around the room and can choose between effects mimicking
a small, medium or large room.
The system was demonstrated for 快猫短视频 at Dolby鈥檚 offices in
San Francisco last week, and we can report that the surround-sound effect in
headphones is indeed convincing鈥攅ven with the tiny earpieces used with
personal stereos. The first Dolby Headphone home processors go on sale early
next year.