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Home Theater Handbook

Multichannel systems

Part 2

See also: all questions, part 1

Which compression algorithm is used by DTS and what is the average data reduction?

DTS approached the subject of data compression from a different technical and philosophical way and applied the Coherent Acoustics algorithm. This algorithm applies a compression of 4:1. This fact of course means that DTS takes up more space than Dolby Digital in any storage media and the lower compression promises better sound. The DTS format specifies three channels (Left, Center, Right) with a frequency response of 20 Hz to 20 kHz, two surround channels with frequency response of 80Hz to 20 kHz and one Low Frequency Effects (LFE) channel with frequency response of 20-80 Hz.

What are the predetermined roles of the speakers used in a Dolby Digital 5.1 or DTS system?

The roles and the specifications of the six audio channels of DD5.1 and DTS are strictly predetermined. The front left and right speakers carry the main responsibility of reproducing music and special effects, the front central speaker handles the dialogues and any sounds that the director wishes to emanate from the center of the screen.

The LFE (Low Frequency Effects) channel reproduces the very low frequency effects that we mostly feel instead of hear. The LFE carries no high frequencies and has a cutoff frequency of 120 Hz for Dolby Digital 5.1 and 80 Hz for DTS.

What is the role of the Subwoofer in a Dolby Digital 5.1 or DTS system?

We must emphasize that in a Dolby digital 5.1 or DTS system, the subwoofer is not exclusive to the LFE reproduction but may also reproduce the bass of any speaker that we desire. If we therefore have small speakers without adequate bass response, we can steer the bass to the subwoofer.

What is the role of the surround speakers?

The surround speakers must have the capability to reproduce intense sound effects at high levels and discrete information for the left and right surround channels.

What is the solution to improving the perception of rear surround sound?

The great success of the digital 5.1 systems is the result of the impressive three-dimensional sound they reproduce. These systems specify three front speakers two surround speakers and a subwoofer.

Research however has proved that humans have a greater difficulty in perceiving rear surround sounds. In order to emphasize the rear sound image it was decided to call for a rear center surround speaker.

Dolby-EX is therefore a seven-channel format. It is the result of the cooperation between Dolby Laboratories Inc and THX. The first movie with such sound format was the "Star Wars: Episode 1 - The Phantom Menace" that came out in 1999.

How did DTS respond to the Dolby-EX introduction?

The response from DTS came soon after the Dolby-EX introduction, by the introduction of two new systems, the DTS Matrix 6.1 and DTS-ES 6.1 Discrete.

"5.1" and "6.1" systems are compatible. How is this possible?

The 6.1 speaker arrangement includes a rear center channel, which is placed between the two existing rear speakers to eliminate any vagueness and instability in the rear surround sound effects that must be placed exactly behind us. Luckily for the consumers the 6.1 systems are compatible with 5.1 systems. If an A/V receiver has a 5.1 decoder, the sound information for the rear center channel will be equally split between the two rear channels and will not be lost.

How does DD Surround EX differ from DD 5.1?

Dolby Digital Surround EX is the evolution of Dolby Digital 5.1; the only difference between the two is the additional rear center channel. Dolby Digital Surround EX specifies sound reproduction by six audio channels, with frequency response of 20 Hz to 20 kHz and an LFE channel with a response of 20Hz to 120Hz.

Is the backward compatibility of the system ensured?

The backward compatibility of the system is ensured by the fact that the additional information is encoded using the matrix method in the existing two rear channels specified by 5.1 systems. A 5.1 decoder reproduces the additional information by the two rear channels while a 6.1 decoder extracts the information and reproduces it by a discrete center rear channel.

What advantages derive from the addition of the rear center surround channel?

The addition of the rear center surround channel is a definite improvement over the 5.1 system, Ideally we will use a separate speaker for its reproduction. The reproduced sound this way literally surrounds the audience and the sound movements between the axes defined by the speakers are more realistic and detailed.

How do DTS-ES 6.1 Matrix and DTS- ES 6.1 Discrete systems differ?

DTS introduced two 6.1 systems, first the Matrix and then the Discrete. The DTS-ES 6.1 Matrix uses the matrix encoding technique to add the additional rear channel information to the two existing channels. The DTS-ES 6.1 Discrete system encodes the rear center channel as a discrete channel. This two pronged approach was the result of DTS's desire to keep backward compatibility with the Matrix system, while also introducing a no compromise Discrete system.

How is the backward compatibility of the system ensured?

The backward compatibility with DTS is ensured due to the original specifications of DTS that foresee up to eight discrete channels. The 5.1 channels are handled as main channels and the additional channels as expansion channels. The 5.1 decoders of regular DTS ignore the additional channel, while 6.1 decoders process the information to generate the seventh discrete channel. Movies that carry DTS-ES 6.1 Discrete soundtrack also carry Matrix encoded information for the rear center channel, for compatibility purposes.

What led to the introduction of DPL 11 and DTS Neo 6 decoders?

Up to recently Dolby Pro Logic decoders performed the multichannel decoding of audio information from a two channel, matrix-encoded analog signal. However discrete digital systems are superior to analog systems. The need to improve the reproduction of two channel matrix signals and to be able to perform multichannel reproduction of simple stereo signals led to the introduction of two new decoders. Dolby created the Dolby Pro Logic 11 decoder and DTS created the DTS NEO 6 decoder.

What is the difference between Dolby Pro Logic and Dolby ProLogic II?

Dolby Pro Logic II is the replacement of Dolby Pro Logic system. The main difference between the two formats is the full frequency response of the surround channels, which are now also stereo.

What are the two modes of operation of Dolby ProLogic II?

Dolby Pro Logic 11 has two discrete ways to operate, Movie and Music, based on the reproduction of a soundtrack or music. DPL II has the capability to reproduce exceptional multichannel sound from any analog or digital signal. We can therefore listen to our CDs in multichannel without losing any fidelity and we can watch movies from our stereo VCR with much improved sound.

Why is Dolby Pro Logic 11 superior to Dolby Pro Logic?

Dolby Pro Logic II is an important step forward in the field of multichannel sound reproduction from a two channel signal. The sound quality in the Movie setting approaches that of Dolby Digital and is superior to Dolby Pro Logic, since the sound is clear, the dialogues are more distinct, the sound effects are more realistic and convincing. In the Music setting Dolby Pro Logic 11 is again far superior to Dolby Pro Logic. We can modify the center channel level by adjusting the Center Width Control, we can move the sound stage to the front or to the rear with the adjustment of the Dimension Control and we can modify the width of the sound stage with the adjustment of the Panorama setting.

Why should be Dolby Pro Logic 11 be part of every home entertainment system?

The introduction of Dolby Pro Logic 11 makes Dolby Pro Logic obsolete from every point. DPL 11 is a decoding system that must be a part of every home entertainment system due to the great number of two channel audio sources.

What is DTS NEO:6?

DTS NEO:6 is respective to Dolby Pro Logic II. It has the capability to reproduce any analog or digital two-channel signal with multichannel sound.

DTS NEO:6 also has two operation settings, Movie and Music. DTS Neo:6 gives an impressive multichannel reproduction of regular two-channel stereo movie soundtracks and music CDs.

What is the difference of today's multichannel sound formats from the Quad system of the 70s?

  • First of all in contrast to today's multichannel systems, the manufacturers of Quad never agreed on common technical specifications and their systems were therefore non compatible.
  • In addition the Quad systems were very peculiar about speaker placement and created many audio artifacts and a "floating" sound stage in contrast to contemporary systems that with the use of the front main and center speakers, "anchor" the sound, creating a very stable and realistic audio image.

My A/V amplifier has a Dolby Digital decoder. Why do I need a Dolby Pro Logic II decoder?

  • There is no doubt that Dolby Digital is superior to Dolby Pro Logic II. However Dolby Digital is only available from DVDs and digital TV.
  • Dolby Digital can not reproduce the sound from videotapes or regular broadcast TV. For these sound sources Dolby Pro Logic 11 reproduces an excellent sound that comes close to Dolby Digital quality.

Can I use the "A" speaker outputs of my amplifier to drive surround speakers?

  • This is a fairly common question and the answer is a resounding NO! The "B" speaker outputs have the same exact signal as the "A" speaker outputs and are used to connect a second pair of speakers that plays in a different room.
  • The surround speakers are fed with a different signal from the main speakers, which is obtained after the decoding of the audio signal by a multichannel decoder.

What kind of speakers are suitable for surround use? Do I need special speakers?

  • The surround speakers are responsible for the reproduction of the diffused sound effects that are included in an audio signal.
  • The surround speakers must be "matched" acoustically with the main speakers, must reproduce the full audio frequency spectrum, must fit with the room's decoration and must be easy to place.
  • The OQx system specifies the use of dipole speakers for an even more realistic reproduction of surround sound effects.

Can I use my TV's speakers instead of a center speaker?

  • Theoretically yes, as long as you're A/V amplifier has a preamplifier output for a center speaker and the TV a preamplifier input for the same. However we do not recommend this solution, since the center speaker is very important for the system's performance and requires high fidelity.
  • Most TVs have medium or low quality speakers that do not meet the required specifications.

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