Sony G90 Logic 7 Digital Signal Processing for Movies and Music, Lexicon’s Music Surround Modes

Models: G90

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ment. A “Bass Split” feature takes bass infor-

mation filtered from the center channel

(assuming you have a small center speaker)

and directs it to the left and right channels.

Inside, the MC-1 uses AD converters and

DACs from a company called AKM. Both are delta-sigma

devices that are supposedly better performing than the con-

verters used in most controllers. Note that both are always in

the signal path, meaning that all analog signals are converted

to digital upon entering the MC-1 and then converted back to

analog at the output. If you have a High End turntable or dig-

ital source (I used a Krell KPS-25s and a Mark Levinson

No.31.5 transport and No.360s processor), the MC-1’s digital

conversions will degrade the sound quality. There’s no

“bypass” mode that directs an analog signal to the output

unaltered. This is, in my view, a serious shortcoming.

I’ve used many controller and A/V receiver remotes;

this is one of the best. The MC-1 needs a good remote

because the machine is extremely complex. There are four

layers of menus incorporating 17 submenus. This opera-

tional complexity goes with the territory on a controller

with as many features as the MC-1. No fewer than 24

effects are provided, including simulated acoustic spaces

(Concert Hall, Night Club), various film-soundtrack modes

(Dolby Digital, THX 5.1, DTS), Lexicon’s Logic 7 process-

ing, and music surround.

Logic 7 Digital Signal Processing for

Movies and Music

Logic 7 is Lexicon’s proprietary technique for generating multi-

channel playback from two-channel sources. Logic 7 processing

can also “enhance” existing 5.1-channel programs such as Dolby

Digital and DTS for seven-channel reproduction. Lexicon pro-

motes Logic 7 as a universal format for distributing multi-chan-

nel music over two-channel formats such as CD and television or

radio broadcasts. These programs can be Logic 7 encoded to

achieve the full surround-sound effect, or unencoded (such as on

existing CDs) and still create surround-sound playback.

When reproducing 5.1-channel sources (Dolby Digital and

DTS) with Logic 7 and seven loudspeakers, the MC-1 sends

the right surround signal to the right side and right rear speak-

ers, and the left surround signal to the left side and left rear

speakers. This is identical to wiring two surround speakers to

each surround channel. But as sound effects pan toward the

rear, the Logic 7 algorithm uses equalization to “steer” sur-

round signals between the two side and two rear speakers.

Specifically, effects moving from the left to rear pan smooth-

ly from the left front loudspeaker to the left side, then from

the left side to both left and right rear speakers. When effects

are moving toward the rear, Logic 7 adds a 3dB treble cut

(shelf filter) to the side speaker. As the sound further pans to

the rear, the frequency at which the shelf filter begins attenu-

ating is lowered, further reducing the treble sent to the side

speaker. When the sound is fully to the rear, a 6dB per octave,

400Hz low-pass filter is applied to the side speakers. The

result is an apparent separation between the side and rear

channels that heightens the feeling of envelopment, and of

sounds in motion.

Lexicon’s Music Surround Modes

The music-surround modes are as innovative as Logic 7. The

music modes are divided into two categories, ambiance

extraction and ambiance generation. In the latter modes, the

MC-1 generates new signals (reverberation) that drive the

side and rear speakers. In the extraction modes, the MC-1

simply recovers ambiance information from the existing sig-

nal for reproduction by the side and rear speakers. The

extraction modes are much more subtle, and, in my view,

more musically appropriate. Nonetheless, the ambiance-gen-

eration modes driving seven loudspeakers can produce some

startling results.

The music modes use a variety of processes to increase

the sense of spaciousness and create a feeling of being

enveloped in an acoustic larger than that of your listening

room. Some of the MC-1’s modes use a crosstalk-cancellation

trick to widen the soundstage. Crosstalk occurs when sound

from the left speaker reaches the right ear, and vice versa.

Lexicon’s booklet that accompanies the MC-1 explains

crosstalk cancellation: “Imagine there is a sound coming from

the left channel only. This sound will travel to the left ear of

the listener, then diffract around the listener’s head and be

heard by the right ear. If we take the left-channel sound, delay

it just the right amount, invert it in phase and feed it to the

right speaker, it will arrive at the right ear just in time to can-

cel the crosstalk from the left speaker.”

Although crosstalk cancellation has been used in other

products (where it has been called a variety of trade names),

the MC-1’s implementation is considerably more sophisticat-

ed. The simple technique described above can introduce col-

orations because the cancellation signal becomes audible.

Lexicon uses a multi-order cancellation technique in which

the cancellation signal is itself canceled by a second signal,

and that signal canceled by a third, and so on. Reducing this

“inter-aural crosstalk” by adding cancellation signals can

make the sonic presentation appear wider.

These are just a few of the processes, used individually or

in combination, by which the MC-1 creates multi-channel sur-

round playback from two-channel sources. Other equally

interesting techniques are also employed that space restric-

tions prevent me from describing.

Listening to Movies

For starters, the MC-1 in straight decoding mode (Dolby Pro

Logic, Dolby Digital, and DTS), or those formats with THX

processing, was superb sounding. The MC-1 had outstanding

dialog clarity and intelligibility, even with the center-channel

level perfectly matched to the other channels. With lesser

products, I find myself increasing the center-channel level a

couple of decibels to make the dialog easier to hear. The MC-

1’s good resolving power and image solidity seemed to

anchor the dialog right on the screen (it helps to have a

superlative center-channel speaker like the Revel Voice).

This impression of tight center-channel focus and clarity

was particularly impressive with matrixed Dolby Surround

sources, which often lack the image specificity and clarity of

discrete multi-channel sources. The MC-1’s Pro Logic

decoding made matrixed sources sound more like discrete

soundtracks, with greater apparent channel separation,

smoother pans, and increased clarity compared with other

Pro Logic decoders.

Even without any additional processing, the impression of

envelopment from the surround channels was exceptional. The

MC-1 seemed to create a spaciousness behind me, along with a

smooth transition between the front and rear speakers. More-

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Sony G90 manual Logic 7 Digital Signal Processing for Movies and Music, Lexicon’s Music Surround Modes, Listening to Movies