| Surround sound is the concept of expanding the spatial | | | | DTS is an encode/decode process that delivers 5.1 |
| imaging of audio playback from 1 dimension (mono | | | | channels of "master quality" audio on CD, CD-R, and |
| Left-Right) to two or three dimensions. It is often | | | | DVD. Each DTS encoded disc represents a sonic |
| employed for a more realistic audio environment, | | | | "clone" of the original film soundtrack. |
| actively implemented in cinema sound systems, | | | | The difference between Dolby Digital (AC-3) and DTS |
| technical theatre, home entertainment, video arcades, | | | | is: |
| computer gaming, and a growing number of other | | | | -DTS provides a deeper and tighter low frequency |
| applications. Many popular surround sound formats | | | | presence |
| have evolved over the years. They include ambisonics, | | | | -DTS allows the sound to breath - transparency |
| quadraphonic, Dolby 5.1 Surround sound, DTS, and MP3 | | | | -AC-3 leaves the impression that something is missing |
| Surround. | | | | from the mix |
| Surround sound can be created using several | | | | -At lower bit-rate AC-3 starts to sound like MP3's |
| methods. The simplest to understand uses several | | | | encoded at a low-quality 96kbps (artifacts) |
| speakers around the listener to play audio coming from | | | | DTS is more three dimensional. The sound actually |
| different directions. Another approach involves | | | | moved forward from the individual speakers to sound |
| processing the audio using psychoacoustic sound | | | | more full. This fullness was most apparent with the |
| localization methods to simulate a 3D sound field using | | | | music. Instead of simply coming from the speakers, the |
| headphones. The third approach, wave field synthesis, | | | | DTS filled the front soundstage not only side to side, |
| uses a very large number of speakers to generate | | | | but with more depth as well. Bass reproduction was |
| the "audio hologram" of the original audio in the whole | | | | also more defined in the DTS version, leaving the DD |
| room (as of 2004 the only commercial implementation | | | | edition sounding muddy. |
| of this is Iosono). Surround sound is not limited to | | | | Dolby Digital incorporates dialog normalization, which |
| placement of speakers along a flat (2-dimensional) | | | | alters the decoded level of the soundtrack. The typical |
| plane. Vertically-located audio sources can be | | | | setting reduces level by 4 dB; other reduction levels |
| considered. | | | | are possible. In most decoders, this leads to a reduction |
| Dolby Digital (DD) uses the AC-3 file format, which any | | | | in signal-to-noise and dynamic range. |
| Dolby Digital Decoder can decode to produce 5.1 audio. | | | | Dolby Digital also provides a "stereo down mixing" |
| Dolby Digital is the technical name for Dolby's | | | | feature as a substitute for a dedicated stereo mix. |
| multi-channel digital sound coding technique, more | | | | However, many production engineers have admitted |
| commonly referred to as Dolby 5.1. A six-channel | | | | that they often have to modify the original 5.1 mixes in |
| sound coding process originally created by Dolby for | | | | order to attain acceptable stereo down mixes. |
| theaters, AC-3 was subsequently adapted for home | | | | Therefore, the 5.1 mix on many Dolby Digital DVDs |
| use and is now steadily becoming the most common | | | | may differ from the original master. |
| sound format for DVD. | | | | 5.1 Surround Sound Headphones: |
| Six discrete audio channels: | | | | While the traditional method of surround sound |
| -3 for speakers at the front - left (L), center (C), and | | | | described above uses numerous speakers to produce |
| right (R) | | | | the entire sound field, the surround sound mix is limited |
| -2 for surround speakers at the side or rear - surround | | | | to a two-channel stereo mix when using headphones. |
| left (SL) and surround right (SR) | | | | That is why recent developments in surround sound |
| -1 low-frequency effects (LFE) channel carries | | | | technology include 5.1 surround sound headphones, to |
| supporting deep bass sound effects, ranging from 10 | | | | allow you to have the same sound quality and |
| Hz to 120 Hz, which can for example be used by a | | | | surround sound experience without waking the |
| subwoofer. (This is the '.1' in '5.1'.) | | | | neighbors or disturbing roommates. |