Ever since stereo sound became popular in the 1950s, the race has been on to create the best home listening experience. Already in the 1930s there were surround sound experiments . In 1940, Walt Disney introduced his innovative surround sound technology fantasound to fully immerse the audience in both the visual and audio experience of their animated achievement Fantasia .

Although Fantasound and other early experiments in surround sound technology could not be duplicated in a home setting, this did not limit the ability of music and film recording engineers to develop processes that would eventually lead to surround sound formats. used today in home theaters around the world.

What is monophonic sound?

Monaural (mono) sound is a single-channel, unidirectional type of sound reproduction. All sound recording elements are routed using a single amplifier and speaker combination. No matter where you stand in the room, you hear all elements of the sound the same (with the exception of acoustic variations in the room). At first glance, all elements of sound, voice, instruments and effects come from the same point in space. As if everything is «directed» to one point «in front» of the listener. If you connect two speakers to a mono amplifier, the sound will play at a point equidistant between the two speakers, creating a «phantom» channel.

What is stereo sound?

Stereophonic (stereo) sound is a more open type of sound reproduction that allows the listener to properly appreciate the sound of a performance. Through the channels of the left and right speakers, the impression of sound is coming from all directions around the listener, and not just from one point.

Stereophonic process

The main aspect of stereo sound is the separation of sounds into two channels. The recorded sounds are mixed in such a way that some elements are sent to the left side of the sound stage and others are sent to the right side.

One of the positive results of stereo sound is that listeners experience the sound staging of symphony orchestra recordings, where sounds from different instruments emanate more naturally from different parts of the stage. However, solid color elements are often still included. By mixing the lead vocalist in the band in both channels, the vocalist appears to be singing from a «phantom» center channel, between the left and right channels.

Stereo audio limitations

Stereophonic Sound was a breakthrough for consumers in the 50s and 60s, but it has its limitations. At the time, some recordings resulted in a «ping-pong» effect, where the mix emphasized the difference in the left and right channels too much while undermixing the elements in the «phantom» central channel . Also, while the sound was more realistic, the lack of ambiance information such as acoustics or other elements left a «wall effect» stereo sound in which everything hit you from the front and lacked the natural sound of back wall reflections. . or other acoustic elements.

Four-channel discrete audio

In the late 60s and early 70s, two developments occurred that attempted to remove the limitations of stereo: four-channel discrete and quadraphonic audio.

Four-channel discrete audio requires four identical amplifiers (or two stereo amplifiers) to reproduce the sound. While this provided rich and impressive sound reproduction, it was extremely expensive in the days of tubes and transistors rather than integrated circuits and microcircuits.

In addition, such sound reproduction was indeed available only through broadcast media, that is, two FM stations, each of which broadcasts two channels of the program simultaneously. This means you’ll need two tuners to get it all the way, as well as four-channel sound decks, which were also expensive.

Also, vinyl records and turntables cannot handle four-channel discrete recordings. Although several interesting musical performances were broadcast simultaneously using this technology (with the help of a co-operating television station broadcasting video), the entire installation was too unwieldy for the average consumer.

Quadraphonic Sound: A More Realistic Approach

Taking a more realistic and accessible approach to surround sound reproduction, the quad format consisted of matrix encoding four channels of information in a two-channel recording. The practical result is that ambient sounds or effects can be embedded in a two-channel recording that can be extracted with a conventional phono stylus and passed to a receiver or amplifier with a quad decoder.

In essence, Quad was the forerunner of today’s Dolby Surround. In fact, if you have any old quad-core hardware, it is capable of decoding most analog Dolby Surround signals. Although Quad has promised to bring affordable surround sound to the home environment, the need to purchase new amplifiers, receivers and speakers—not to mention the lack of standardization among hardware and software manufacturers—caused Quad to fall before it could take hold.

The advent of Dolby Surround

In the mid-70s, Dolby Labs — with breakthrough movie soundtracks like » Tommy» » Star Wars» and » Close Encounters of the Third Kind introduced a new surround sound process that is easier to adapt to home use. With the advent of the HiFi stereo VCR and stereo television broadcasting in the 1980s, another path to surround sound emerged: the home theater. Up to this point, listening to the audio portion of a television broadcast or a VCR tape was like listening to a desktop AM radio.

Dolby Surround Sound: practical for the home

With the ability to encode the same surround sound information into a two-channel signal that was encoded in the original movie or TV soundtrack, there is a new incentive for software and hardware manufacturers to make affordable surround sound components. Additional Dolby Surround processors are available for those who already own stereo receivers. As the popularity of this experience reached more and more homes, more affordable audio receivers and Dolby Surround amplifiers became available. Eventually, this made surround sound a permanent fixture in home entertainment.

Basics of Dolby Surround

The Dolby Surround process encodes four channels of information: front left, center, front right and surround back into a two-channel signal. The decoding chip decodes four channels and sends them to the corresponding destination. (Center channel derived from equal balance of left/right channels.)

The result of Dolby Surround mixing is a more balanced listening environment in which the main sounds are output from the left and right channels, vocals or dialogue come from the phantom center channel, and ambience or effect information comes from behind the listener.

Music encoded with this process has a more natural-sounding sound with better acoustic signals. In movie soundtracks, the sensation of sounds moving from front to back and from left to right adds realism by putting the viewer at the center of the action.

Limits of Dolby Surround

However, Dolby Surround has its limitations. Since the rear channel is mostly passive, it lacks precise directivity. In addition, the overall distance between channels is much smaller than with conventional stereo recording.

Dolby Pro Logic

Dolby Pro Logic removes the limitations of standard Dolby Surround by adding into the hardware decoding chip software and hardware elements that emphasize directional signals. In other words, the decoding chip will add emphasis to directional sounds by increasing the output of directional sounds in their respective channels.

This process, although not as important when recording music, is effective for movie soundtracks. With greater channel separation, it enhances the fidelity of sound effects such as explosions, gunfire, aircraft, and other sounds. In addition, Dolby Pro Logic highlights a dedicated center channel that more accurately centers dialogue. (This requires a center channel speaker for full effect.)

Limits of Dolby pro-logic

While Dolby Pro-Logic is a great enhancement to Dolby Surround, its effects are purely based on the playback process. Although the surround back channel uses two speakers, they still transmit a mono signal, limiting motion signals and rear-to-front and side-to-side sound placement.

Dolby Digital

Dolby Digital often referred to as a 5.1 channel system. However, it should be noted that the term «Dolby Digital» refers to the digital encoding of an audio signal, not how many channels it has. In other words, Dolby Digital can be mono, 2ch, 4ch, 5.1ch, or 6.1ch. However, Dolby Digital 5.1 and 6.1 are simply referred to as «Dolby Digital» in their most common applications.

Benefits of Dolby Digital 5.1

Dolby Digital 5.1 adds precision and flexibility by adding surround back channels. This allows sounds to come from different directions, as well as a dedicated subwoofer channel to provide more emphasis on bass or low frequency effects. The subwoofer channel is where is taken designation .1 .

Also, unlike Dolby Pro Logic, which requires a rear channel with minimal power and limited frequency response, Dolby Digital encoding and decoding requires the same output power and frequency range as the main channels.

Dolby Digital encoding started on laserdisc and moved to DVD and satellite programming, solidifying the format in the market. Since Dolby Digital includes its own encoding process, you will need a Dolby Digital receiver or amplifier to accurately decode the signal. The signal is transmitted from a component, such as a DVD player, through digital optical or digital coaxial compound.

Dolby Digital EX

Dolby Digital EX is based on technology already developed for Dolby Digital 5.1. This process adds a third surround channel that is placed directly behind the listener.

In other words, the listener has both a front center channel and, with Dolby Digital EX, a rear center channel. If you lose count, the channels are tagged: Front Left, Center, Front Right, Surround Left, Surround Right, Subwoofer, Surround Center Surround (6.1), or Surround Back Left and Surround Back Right. This obviously requires a different amplifier and a dedicated decoder in the surround A/V receiver.

What is the advantage of Dolby Digital EX?

In Dolby Digital, most of the surround sound effects move towards the front or side of the listener. However, the sound loses some directionality as it travels along the sides towards the back, making it difficult to convey an accurate directional sense of moving or panning sounds around a room. By placing the new channel directly behind the listener, the panning and positioning of sounds coming from the sides to the rear is much more accurate. In addition, thanks to the additional rear channel, tonal sounds and effects can be detected more accurately. This allows you to put the listener at the center of the action.

Dolby Digital EX Compatible

Dolby Digital EX is fully compatible with Dolby Digital 5.1. Because Surround EX signals are matrixed into a Dolby Digital 5.1 signal, EX-encoded software titles can still be played on existing DVD players with Dolby Digital outputs and decoded in 5.1 on existing Dolby Digital receivers.

While you may end up buying new EX-encoded versions of movies you already have in your collection, you can still play your current DVDs through a 6.1 channel receiver. You will also be able to play your new EX-encoded discs through the 5.1-channel receiver, which will store the new information with the current 5.1-channel surround scheme.

Dolby Pro Logic II and Dolby Pro Logic IIx

While the previously described Dolby surround sound formats are designed to decode audio that is already encoded on DVD or other material, there are thousands of CDs, VHS tapes, laserdiscs, and television broadcasts that contain simple analog two-channel stereo or Dolby Surround encoding.

In addition, when using schemes surround sound such as Dolby Digital and Dolby Digital-EX, primarily designed for watching movies, there is no effective surround sound process for listening to music. In fact, many discerning audiophiles reject most surround sound schemes, including the new multichannel audio formats SACD (Super Audio CD) and DVD-Audio, in favor of traditional two-channel stereo playback.

Some manufacturers such as Yamaha have developed sound enhancement technologies (called DSP — Digital Sound Field Processing) that can place the source material in a virtual sound environment such as a jazz club, concert hall or stadium, but cannot «convert» two or four channel material to a format 5.1.

Benefits of Dolby Pro Logic II Audio Processing

With this in mind, Dolby Labs has come to the rescue by refining its original Dolby Pro-Logic technology, which can create a «simulated» 5.1-channel surround sound environment from a 4-channel Dolby Surround (Pro Logic II dubbed) signal. Although it is not a discrete format like Dolby Digital 5.1 or DTS, in which each channel goes through its own encoding/decoding process, Pro Logic II makes good use of matrixing to provide an adequate 5.1 representation of movie or music soundtracks. With technological advances since the original Pro-Logic circuitry was developed over 10 years ago, channel separation has become more precise, giving Pro Logic II the character of a discrete 5.1-channel circuitry.

Extracting surround sound from stereo sources

Another advantage of Dolby Pro Logic II is the ability to adequately create a surround sound listening experience from two-channel stereo recordings. We were less than satisfied trying to listen to two-channel surround-sound music recordings using standard Pro Logic. Vocal balance, instrument placement and transitional sounds always seem to be somewhat unbalanced. Of course, there are many Dolby Surround or DTS encoded CDs. Some of them are mixed for surround listening, but the vast majority do not use and can benefit from the Dolby Pro Logic II enhancement.

Dolby Pro Logic II also has several settings that allow the listener to tailor the soundstage to suit particular tastes. These settings are:

  • Size control which allows users to adjust the soundstage either forward or backward.
  • Adjustment central width which allows you to change the center image setting so that it can be heard only from the center speaker, only from the left/right speaker, or through combinations of all three front speakers.
  • panoramic mode, which expands the front stereo image to include the surround speakers for a wraparound effect.

The final benefit of the Pro Logic II decoder is that it can also operate as a «regular» 4-channel Pro-Logic decoder. Essentially, this means that receivers with Pro Logic decoders can also include Pro Logic II decoders, giving the consumer more flexibility without the expense of two different Pro Logic decoders in the same unit.

Dolby Pro Logic IIx

A more recent variant of Dolby Pro Logic II is Dolby Pro Logic IIx, which expands the extraction capabilities of Dolby Pro Logic II, including its preference settings, to 6.1 or 7.1 channels receivers and preamplifiers equipped with Dolby Pro Logic IIx. Dolby Pro Logic IIx is designed to extend the listening experience to more channels without the need to remix or re-release the original material. This makes your recording and CD collection highly adaptable to the latest listening environments.

Dolby Prologic IIz

Dolby Prologic IIz processing is an extension that expands surround sound vertically. Dolby Prologic IIz offers the possibility to add two more front speakers, which are located above the left and right main speakers. This feature adds a «vertical» or top component to the surround sound field, which is great for rain, helicopter or airplane effects. Dolby Prologic IIz can be added to either a 5.1 or 7.1 channel setup.

Yamaha offers a similar technology for some home theater receivers called Presence.

Dolby Virtual Speaker

While the surround sound trend is based on adding more channels and speakers, the requirement to have multiple speakers throughout the room is not always practical. With this in mind, Dolby Labs has developed a way to create a fairly accurate surround sound effect that gives the illusion that you are listening to a full surround sound system using only two speakers and a subwoofer.

Dolby Virtual Speaker creates a wider soundstage when used with standard stereo sources. However, when stereo sources are combined with Dolby Prologic II or Dolby Digital DVDs are played, the Dolby Virtual speaker creates a 5.1-channel picture using technology that takes into account sound reflection and how people hear sound in their natural environment, ensuring the signal is reproduced without the need for five or six speakers.

Audyssey DSX (or DSX 2)

Audyssey, a company that develops and markets automatic speaker equalization and correction software, has developed its own immersive surround sound technology: DSX (Dynamic Surround Expansion).

DSX adds vertical height front speakers similar to the Prologic IIz, but also includes the addition of left/right wide speakers positioned between the front left and right and surround left and right speakers. For a more detailed explanation and illustrations of speaker setup, visit the official Audyssey DSX page .


DTS is another famous surround sound player that has adapted the surround sound process for home use. Basic DTS is a 5.1 system, the same as Dolby Digital 5.1, but since DTS uses less compression in the encoding process, many people think that DTS has a better result on the listening side. While Dolby Digital is primarily for watching movies, DTS is also used for mixing and playing music.


DTS offers its own 6.1 channel systems in competition with Dolby Digital EX called DTS-ES Matrix and DTS-ES 6.1 Discrete. In essence, DTS-ES Matrix can create a center back channel from existing DTS 5.1 encoded material, while DTS-ES Discrete requires software to already have a DTS-ES discrete audio track. As with Dolby Digital EX, DTS-ES and DTS-ES 6.1 discrete formats are backward compatible with DTS 5.1 receivers and DTS-encoded DVDs.

DTS Neo: 6

In addition to DTS 5.1 and DTS-ES Matrix and Discrete 6.1 formats, DTS also offers DTS Neo: 6 . DTS Neo:6 functions similarly to Dolby Prologic II and IIx. With receivers and preamps that have DTS Neo:6 decoders, it will extract a 6.1-channel surround sound field from existing analog two-channel material.


The next step that DTS has taken is the introduction of 11.1-channel format Neo:X. DTS Neo:X takes signals already present in 5.1 or 7.1 channel soundtracks and creates height and wide channels for a more enveloping «3D» sound. To get the most out of DTS Neo:X processing, it’s best to have 11 speakers with 11 channels of amplification and a subwoofer. However, DTS Neo:X can be modified to work with a 9.1 or 9.2 channel configuration.

DTS Surround Sensation

Surround Sensation creates phantom center, left, right and surround channels in settings two speakers or stereo headphones . It can take any 5.1 channel input source and recreate surround sound with just two speakers. In addition, the surround sound experience can also expand two-channel compressed audio signals (such as MP3) for more surround sound.

SRS/DTS Tru-Surround and Tru-Surround XT

SRS Labs is another company that brings innovative technology to enhance the home theater experience. (SRS is now part of DTS.)

Tru-Surround has the ability to accept multi-channel encoded sources such as Dolby Digital and reproduce the surround sound effect using only two speakers. The result is not as impressive as Dolby Digital 5.1. The front and side surround effects are impressive, but the rear surround effects are a little behind, in the sense that they come not only from the back of the room, but also from the back of the head. However, since many consumers don’t want to fill their room with six or seven speakers, Tru-Surround and Tru-SurroundXT offer the opportunity to enjoy 5.1 channel audio in the normally limited two-channel listening environment.

SRS/DTS Circle Surround and Circle Surround II

Circle Surround is uniquely suited to surround sound. While Dolby Digital and DTS strive for precise directional experience with specific sounds coming from specific speakers, Circle Surround emphasizes the immersion of the sound. To do this, a normal 5.1 audio source is encoded into two channels, then re-decoded back into 5.1 channels, and redistributed back to 5 speakers (plus a subwoofer). This is done in such a way as to create a more immersive sound without losing the direction of the original 5.1 channel source material.

The results are more impressive than Tru-Surround or Tru-Surround XT.

First, panning sounds such as flying planes, speeding cars and trains are heard even when crossing the soundstage. Often in DD and DTS, panning sounds will «fall off» in intensity as they move from one speaker to the next.

Sounds from back to front and front to back flow more evenly. Ambient sounds such as thunder, rain, wind and waves fill the sound field much better than in DD or DTS. For example, instead of hearing rain coming from multiple directions, points in the sound field between those directions are filled in, so you’re in the rain instead of just listening to it.

Circle Surround provides an enhancement to Dolby Digital and similar surround source material without detracting from the original surround sound mixing intent.

Circle Surround II expands on this concept by adding an additional rear center channel, thereby providing anchoring for sounds coming directly from behind the listener.

Headphone surround sound

Surround sound is not limited to large multi-channel systems. This can also be applied to listening through headphones. SRS Labs, Dolby Labs and Yamaha have brought surround sound technology to the headphone listening environment.

Surround headphone options include: Dolby Headphone, CS Headphone, Yamaha Silent Cinema, Smyth Research, and DTS:X Headphones.

Usually when listening to audio (music or movies), the sound seems to come from your head, which is unnatural. Dolby Headphone SRS Headphone, Yamaha Silent Cinema and Smyth Research use a technology that not only gives the listener an enveloping sound, but also removes it from the listening space and places it in the front and side spaces around the head, which is more like listening to a conventional surround sound system. sound.

Alternatively, DTS has developed the DTS:X headphones, which can provide up to 11.1 channel surround sound listening experience using any pair of headphones connected to a listening device such as a smartphone, portable media player, or DTS-equipped home theater receiver. Headphones: X processing.

High-Resolution Surround Sound

With the introduction of Blu-ray Disc and HDMI the development of high-definition (HD) surround sound formats in both DTS (in the form of DTS-HD and DTS-HD Master Audio) and Dolby Digital (in the form of Dolby Digital Plus and Dolby TrueHD) provide enhanced fidelity and realism.

High definition surround sound technologies include: Dolby Digital Plus Dolby TrueHD and DTS-HD Master Audio .

Increased Blu-ray storage capacity and more streaming options HDMI (required to access Dolby Digital Plus, Dolby TrueHD, and DTS-HD) enabled true, discreet audio playback up to 7.1 channels of surround sound. And it’s still backwards compatible with older 5.1 channel surround sound formats and audio/video components.

Dolby Atmos and more

While Dolby Atmos builds on the foundations of previous Dolby Surround Sound formats, Dolby Atmos frees audio mixers and listeners from the limitations of speakers and channels by focusing on where sound should be placed in a 3D environment. More information about technologies, applications and products Dolby Atmos can find in Dolby Atmos — from cinema to home theater.

Additional expanded surround sound formats include:

Conclusion — so far…

Surround sound today is the result of decades of evolution. The surround sound experience is now easily accessible, practical and affordable for home theater enthusiasts, and there’s more to come in the future.

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