What is Dolby and why do you need it?
If you have bought any quality sound components in recent years you will have heard the term Dolby. Most in-car audio and other entertainment products now include Dolby technologies. Dolby technologies are generally held as the "gold standard" for high-quality audio and surround sound in cinema, home theatre systems, and even professional recording studios. But there is more than one type of Dolby sound standard. And despite Dolby having the lion's share of audio-buying awareness, there are other noteworthy companies with in-car audio, such as dts and Logic7. Let's look at them briefly:
Dolby Digital: This is the state-of-the-art 5.1-channel surround format - ie, five full-range channels (left, center, right, left surround, right surround) plus the "0.1" - a low-frequency (bass, or sub-woofer) effects channel. This technology is commonly found in cinemas, DVDs, digital television (HDTV and SDTV) and games. Dolby Digital technology in the car is often built into rear-seat entertainment systems featuring DVD-Video players.
Dolby Pro Logic II: Pro Logic II converts two-channel stereo into natural, richer surround sound and can be incorporated into car sound systems to enhance conventional stereo. Pro Logic II works with any high quality stereo source, including CD, FM radio, cassettes, XM or Sirius satellite radio, and MP3 files.
Dolby Headphone: This technology simulates, through any standard set of headphones, the effect of a 5.1-channel speaker system so convincingly that you tend to forget you're wearing them. In the car, Dolby Headphone technology gives rear-seat passengers the home theatre effect without disturbing the driver.
MLP Lossless: This is the core audio technology behind DVD-Audio, the highest-quality audio format. MLP Lossless technology enables studio master disc-quality audio to be encoded on an optical disc, with no loss in quality. It gives the listener a faithful audio replica of the original studio master, just as it was recorded in the studio. DVD-Audio offers sonic resolution that is 1000 times better than CD quality.
dts: This is an alternative to Dolby Digital and Pro Logic II. Though not as widespread, dts can be found on some DVD-Video players and DVD discs.
Logic 7: Another alternative to Dolby technologies, Logic 7 is found in several new vehicle models, but does not offer its technology to aftermarket products.
Anyone who's ever looked at a set of speakers will know that their power output is rated in Watts. But - here's the point to beware - not all Watts are created equal.
There is only one really helpful power designation for the audiophile and that is RMS, or Root Mean Square. This is the only reasonably accurate, consistent, comparative measurement of power exchange used for amplifiers and speakers.
Sadly, marketing hype drives people to continually increase the "numbers", so quite often the less meaningful "Peak," or "Instantaneous Peak power, or Music Power" watts are given higher prominence.
Peak listing in the amount of power the equipment can handle momentarily--a sharp drum hit, for example. RMS is a better indication of the overall performance, because it is a measurement of the average sustained power.
If only "Watts" or "Peak Watts" are mentioned in the description, the amplifier in question can safely be judged to provide about half that number in true, RMS watts.