Dolby Pro Logic

Dolby Pro Logic is a surround sound processing technology intended to decode soundtracks encoded with Dolby Surround. Dolby Surround Stereo was initially developed by Dolby Laboratories in 1976 for analog cinema sound systems. The format was modified for home use in 1986 as Dolby Surround which was then replaced by the newer and improved Pro Logic system. However, the word "Dolby Surround" is still used to illustrate the encoding technology or matrix-encoded sound, whereas Pro Logic refers to the interpreting technology/processor. It is the home theater edition of the Dolby Stereo technology used in movie cinemas in the 1970s and '80s. In 2000, Dolby launched Dolby Pro Logic II, an enhanced execution of Dolby Pro Logic. DPL II processes any high quality stereo signal source into "5.1"—five separate full frequency channels (left, center, right, left surround and right surround) plus one low-frequency-effects (deep bass) channel.



Dolby Pro Logic II also decodes 5.1 channels from stereo signals encoded in traditional four-channel Dolby Surround. DPL II implements greatly enhanced steering compared to DPL, and as a result, offers an exceptionally stable sound field that simulates 5.1 channel surround sound to a much more precise level than the original Pro Logic. Dolby Surround is the encoding counterpart to Dolby Pro Logic's decoding technology, but early home implementations of Dolby Surround decoding went by the name Dolby Surround which can cause some puzzlement. Dolby Surround and Dolby Pro Logic decoders are similar in principle, as both use matrix technology to extract extra channels from stereo-encoded audio. The beginning of digital formats meant that source content, no longer restricted by the limitations of grooves, multiplexed RF carriers, or tape heads, could expand to 5.1-channel distinct audio as the new standard. When introduced, 5.1-channel Dolby Digital established a wholly new level of soundfield ability and expression. The widespread adoption of Dolby Digital 5.1 audio on DVD-Video discs helped raise the standard and expectations of surround playback in home theaters from that point forward. A Pro Logic II system is set up just like the original Pro Logic system or a Dolby Digital system. Simply tell the receiver if you're using large or small speakers (if this option is offered), and then balance the channel levels using the decoder's test tone. Pro Logic II is available in standalone processors that can be added to existing car audio systems, or as a feature built into OEM and aftermarket car audio systems. Pro Logic II brings all of your old audio software into the 21st century, giving you many of the benefits of Dolby Digital from ordinary stereo software. With its pleasingly simple circuitry and the smoothest steering logic ever, it's a very rare processor really—the kind you'll want to leave on all the time, so you can always enjoy surround sound, no matter what the source.