THX Debuts Spec For Low-Level Surround

SAN RAFAEL, CALIF. — A new specification developed by THX will let home theater users turn down the volume without missing the deep bass, ambient sounds and surround effects typically heard only at higher listening levels.

The technology, called THX Loudness Plus, is the major enhancement appearing in the company's THX Ultra2 Plus and THX Select2 Plus certification standards for A/V receivers. Loudness Plus will appear first in a pair of Yamaha A/V receivers, including the $5,499-suggested RX-Z11 11.2-channel receiver due in November.

THX Loudness Plus incorporates two proprietary technologies called THX Multi-channel Spectral Balancing and THX Dynamic Ambience Preservation. When consumers change the volume level of their home theater system, the system automatically adjusts frequency response and ambient sound levels to compensate for the lower volume to deliver "a more accurate and dynamic listening experience regardless of volume level," the company said.

Deep bass and ambient surround-channel details are often lost in typical home theater rooms, THX explained, because the systems can't be played back at movie makers' reference volume levels without disturbing people in other rooms. Surround soundtracks, THX explained, are "often mixed" in studios at a standardized reference level for movie theater playback. The reference level helps filmmakers mix sound effects, dialogue and the musical score at levels experienced in movie theaters.

Playing back the soundtracks at lower listening levels, however, makes bass sounds, surround effects and ambient sounds much less audible to home theater listeners and deprives them of the ability to hear soundtracks "just like they were mixed in the studio," THX said.

THX Loudness Plus works continuously starting at THX Reference Level "0," which equals 85dB SPL (105dB peak), a spokesman noted. "The lower you turn the volume down, the more compensation is applied," he added.

Here's how the two technologies work: THX Multichannel Spectral Balancing adjusts frequency response "to counter the perceptual loss of low and high frequency sound in all channels," THX explained. Equalization is applied to all channels. At THX reference level, equalization is flat. THX Dynamic Ambience Preservation processing "preserves the spatial detail that is lost when listening below reference level," THX said. This processing "automatically adjusts the front-to-back speaker level relationship … to maintain the perceived balance in the original mix, said Warren Mansfield, THX's consumer technology director.

Multichannel spectrum balancing is needed, he continued, to compensate "for the fact that average level of the surround information is lower than that of the front channels. When the listener turns down the volume below the level that the soundtrack was originally mixed in, surround-channel information is lost due to the threshold of hearing." As a result, the soundtrack would collapse forward without the adjustment, he said.