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Introduction
to the DC-1
Lexicon
2
The key to our perception of the acoustic space we inhabit lies in the lateral
sound field – the sound which moves from side to side in the room. The two
front speakers used in conventional two channel stereo do not adequately
excite these lateral fields in a playback room. The speakers are too far
forward, and the ambient information in the recording is often masked by
the music itself. The DC-1 extracts or synthesizes the ambient information,
and uses additional speakers along the sides and rear of the room to create
a lateral field which closely emulates the original. If the system does not
have side or rear loudspeakers the DC-1 can use panorama technology to
simulate them.
The object is to generate signals for the sides and rear speakers which
recreate the lateral sound missing in conventional stereo. The most basic
approach to this is to analyze the incoming material and extract from it the
information which should be reproduced from the sides and the rear. As
this is also the object of any standard matrix film decoder, one might think
the technology for doing this was well understood, but it is not so easy.
Matrix film decoders evolved from early Quad decoders and are limited to
four decoded channels: front left, front center, front right, and rear. When
the single rear channel is reproduced from multiple speakers in a small
playback room, the sound from the different speakers interferes with itself,
creating a non-enveloping soundfield with an unpleasant timbre. Although
there have been decoders in the past with the ability to separate directionally
encoded effects into more than four directions, they have all suffered from
reduced separation of the rear channels during playback of music. The
DC-1 solves this basic problem with a new idea: a 5 or 7 channel decoder
which is completely compatible with a standard decoder for any directionally
encoded effect, but which maintains the maximum difference between the
left and right side/rear channels at all times.
This new technology is available in the THX and Dolby Digital versions of
the DC-1 in several effects. The basic effect for films is Logic 7, and the basic
effect for music is Music Surround. All the new 5 and 7 channel effects
extract the spatial content hidden in two channel recordings and spread it
convincingly around the listener. All DC-1 matrix decoding algorithms also
include Lexicon’s patented correction circuits for balance and azimuth
errors in the original source material, which make our decoders the most
accurate in the industry. The difference between the new 5 or 7 channel
technology and the older 4 channel technology (also present in the DC-1 as
the Pro-Logic effect and the standard THX Cinema effect) is easily heard
through the increase in envelopment with music or the environmental
sound of any film, and through the increased listener area and spaciousness
on a music CD.
Logic 7 technology also lets us reproduce directionally encoded effects with
left/right separation in the rear. Thus even with a conventional 4-2-4
matrix-encoded soundtrack (Dolby Surround, Ultra*Stereo, etc.) a sound
effect which pans from left to rear will decode in the DC-1 first from the left
front speaker, then from the left side speaker, and finally from both rear
speakers. The results on a film with a good soundtrack are spectacular.