Dolby Pro Logic Adds Height Dimension – Dolby Technologies has – according to their announcement – “taken surround to new heights” with the updating of Dolby Pro Logic IIx to Pro Logic IIz, adding two channels of feeds for a pair of small speakers located above the main front left and right speakers. Pro Logic II is the most widely-accepted technology for creating an immersive surround sound field from most standard two-channel sources. The addition of the x suffix version enlarged the generation of signals to cover 6.1 or 7.1 systems, with one or two center rear speakers. But Dolby points out that many setups cannot accommodate such back speakers due to room layouts and space limitations (frankly, we always thought it was a lousy idea to start with). They have therefore developed this alternative solution, which processes only nondirectional sounds such as ambiance and feeds them to the two height channels so that rain in a film now seems to be actually falling on the viewer’s roof, and orchestral works have more depth, power and presence with the addition of the vertical component.
Dolby carried out extensive listening sessions which established that the height dimension brings out a greater sense of realism than the addition of more surround speakers in the horizontal plane, and especially speakers directly to the rear. They also found that listeners are far more sensitive to directional cues from sounds in front than from those behind, making the front speaker placement ideal, in combination with the standard surround speakers. Yamaha has offered a similar front height feed in their receivers for some time, and at the start of the SACD era Telarc, DMP and Chesky all experimented with SACDs using either the subwoofer or center channel or both for signals picked up by height microphones in the original multichannel recording. But Pro Logic IIz doesn’t require any special encoding or mixing to generate the height signals. Its closest similarity would appear to be to the 2+2+2 Aurophony technology which we are probably the only publication to have been reporting on [check our site search]. The difference is that 2+2+2 requires the original recordings (SACDs and DVD-As) to have been made with additional mikes for the front height channels. Otherwise, Dolby’s placement of the two additional speakers directly above the front left and right speakers seems to be identical to that suggested by Aurophony – at a height of half the distance between the front left and right. In the diagram the speakers are shown to be the smallest in the system, though it would probably be best if they were the same brand and perhaps similar tweeter drivers.
Since the rest of the audio industry is ignoring 2+2+2, one would require a way to switch between a receiver or preamp with Pro Logic IIz outputs and directing the subwoofer and center channel signals to the amps powering the two height speakers for playing of 2+2+2 discs. (We are not ignoring the fact that for many users mounting and setting up these height speakers will be as much of a hassle as would setting up center back channel speakers.) Dolby feels that spatial cues occur naturally in all stereo and surround sources that can be processed by Pro Logic IIz, and they find it especially well-suited to game soundtracks. Onkyo is the first to offer three new home theater receivers with Pro Logic IIz decoding, ranging from $300 to $600. The top TX-SR607 is a 7.2 channel receiver which converts all analog sources to HDMI.