One thing I would like to clarify, whats the difference between:
Dolby Digital
DTS
Prologic
Prologic II
Thanks
Hi mate
You did ask.
Dolby Pro Logic
Dolby Labs (yes, the same people behind Dolby noise reduction in cassette decks) brought out a cinema surround sound technology in 1976. The first movie to use Dolby's technology in a way that wowed the pubic was the Star Wars movie back in 1977.
Dolby Pro Logic is the domestic equivalent. It takes the four channels of surround sound (left, centre front, right and a mono surround channel) from a VHS tape or television broadcast, properly processes the sound and reproduces that sound in your home.
The mono rear channel (shared between two speakers to reduce rear "localisation" create an ambient effect) is bandwidth limited. Frequencies below 100Hz (in the bass) and above 7kHz (in the treble) were taken out of the rear channel speaker feed.
One of the main reasons for the success of Pro Logic is that all of the surround sound information was encoded (or matrixed) within a normal two-channel (stereo) soundtrack.
A VHS videotape and a Nicam TV broadcast can only include two channels of sound. Because of the way Pro Logic is encoded, it survives these two-channel methods of transmission. This means that you can enjoy surround sound from VHS movies (with a hi-fi VCR) and TV broadcasts (with a Nicam-capable TV)
Pro Logic pros: widespread use, large library of movies and programmes
Pro Logic cons: mono surround, poor channel separation
Current uses: television broadcasts, anything on stereo videotape
Dolby Digital
Dolby Labs introduced Dolby Digital in the movie theatres in 1992 with the Batman Returns movie and and became available in the home shortly afterwards. It can also be known as 5.1 (the channel configuration) or AC-3 (Audio Coding 3 - an early code name for Dolby Digital)
Dolby Digital has many advantages over the older Pro Logic. DD offers six discrete (fully separated) channels of sound. There are five full range channels of sound (front left, front centre, front right, surround left and surround right) plus a special sixth channel known as the Low Frequency Effects channel.
While DD is capable of the six separate sound channels, that does not mean that all will be used. An older film with a mono soundtrack may still be encoded in Dolby Digital, but will still have mono sound.
Unlike Pro Logic, the five main channels are full range, which means that they handle the complete range of sounds from 20Hz (very low bass) to 20kHz (very high treble).
The surround channels also differ from Pro Logic in being fully discrete or separate. This means that each surround channel can have differing sounds in it, allowing the sound to move to each channel independently. This can heighten surround effects tremendously.
The sixth channel (Low Frequency Effects or .1) causes much confusion. Many people mistakenly think the the LFE channel is the "bass" channel, which is incorrect.
Some movie theatres have large bass-only speakers, designed for reproducing huge amounts of bass, taking the strain off the main speakers in the movie theatre. When making the film, a sound engineer may choose to put bass heavy sounds into the LFE channel, for use by those movie theatres described.
The confusion arises because many people believe that the LFE channel equates to the frequencies that an AV receiver sends to a dedicated subwoofer. This is not so.
Dolby Digital uses a means of compression to fit all six sound channels on to a DVD. This compression is "lossy" which means that some information is thrown away. Compare this to the computer Zip (PC and Stuffit (Macintosh) compression formats, which are "lossless". With Dolby Digital an encoder chooses the sound most likely to be heard, based on a pyschoacoustic model of human hearing.
Dolby Digital pros: full range discrete channels, becoming ubiquitous
Dolby Digital cons: use restricted to digital formats
Current uses: Dolby Digital can only be found on DVDs (and a few laserdiscs). The digital soundtrack can not be used on VHS videotapes or on stereo broadcast TV.
DTS
DTS (Digital Theatre Sound) is a sound format that competes with Dolby Digital, both in movie theatres and at home on DVDs.
Like Dolby Digital, DTS is a 5.1 surround system with five full range main channels plus a dedicated LFE channel.
DTS uses a different psychoacoustic model for encoding the audio signal. The main difference between DTS and DD is that DTS DVDs are encoded at a higher bit rate for the digital soundtrack.
In theory this should make the soundtrack on a DTS-encoded DVD sound better than an equivalent DD soundtrack. In practise, there is much argument by home theatre aficionados about which format sounds better.
DTS pros: well respected by some movie directors, potentially good sound
DTS cons: lack of movies
Current uses: DTS sound can be found on a limited number of DVDs and some music-only CDs