A Quick Look At Home Theatre Sound Codecs | Rapallo
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Rapallo | Digital Codecs

Written by Deano Lambert, Posted by Deano Lambert

May 26, 2022

This week we have created a guide to the Home Theatre Codecs you see on your AV Receiver. 

Have you ever wondered what those weird names on the front of AV receiver mean, and why when you change the name does the sound drastically change, well we are here to help and to explain what those crazy words mean. Its a bit of a fly-over so not overly in-depth, so as usual, if you are not sure, just give us a quick call and we can fill in the blanks.

Rapallo | Digital Codecs


Dolby Surround Sound is the earliest form of surround sound and is a three-channel system. The Dolby stereo track is decoded into the front left and front right speakers and a mono signal is sent to the two rear surround speakers. Since Dolby Surround signal can be encoded in a stereo analog signal, it is called a “Matrix surround system” (maybe this is where the movie got its name??). The process of extracting several channels from a 2-channel system is called Matrix surround decoding.

Rapallo | Digital Codecs


Dolby Pro Logic was introduced in 1987, the same year that Aretha Franklin was inducted into Rock and Roll Hall of Fame. They added a centre channel to Dolby Surround. So now the four channels were front left, front right, one centre channel, and one mono matrix surround channel. The frequency of the surround channel was limited to 7kHz. Dolby Pro-Logic was available on HiFi VHS and analog TV broadcasts in the United States.

Cables Needed: RCA analog stereo cables.

Rapallo | Digital Codecs


Dolby Digital (also known as Dolby AC-3, short for audio coding 3) was introduced in 1996. Dolby Digital content first appeared on Laserdisc. Hi-Fi VHS only supports Dolby Surround Pro-Logic. Dolby Digital is the standard for DVD-Video and is also part of the High-Definition TV (HDTV) standard in the United States.

The Dolby Digital surround sound format provides up to five discrete full frequency (from 20Hz to 20,000Hz) channels (front left, front right, centre, surround left, surround right), plus an optional sixth channel for Low Frequency Effects (LFE). The low frequency effects channel contains only low bass frequencies (3Hz to 120Hz), ie the subwoofer. 

Dolby Digital offers a maximum bit rate of 640kbps. Both Blu-Ray and HD-DVD players are required to support DD at its maximum bit rate.

Cables Needed: Toslink (Optical) or Coaxial S/PDIF (Sony/Philips Digital Interconnect Format), HDMI, and Multi-Channel Analog Cables.

Rapallo | Digital Codecs


An alternative and competing format to Dolby Digital is DTS Digital Surround. The basic difference between these two formats is the method of compression. The use of DTS Digital Surround is optional on DVDs and it is not supported by HDTV or digital satellite broadcasting in the United States.

Some audiophiles claim that DTS is better in sound quality than Dolby Digital because it offers more data rates. The main disadvantage of DTS is that it uses more disc capacity. There are more DVD titles with Dolby Digital soundtrack than DTS. Both Blu-Ray and HD-DVD players are required to support DTS at its higher 1.5Mbps bit rate.

Cables Needed: Same as Dolby Digital.

Rapallo | Digital Codecs


Atmos is a surround-sound technology that was first developed in 2012, expanding upon the pre-existing 5.1 and 7.1 surround-sound set-ups with surround channels coming from overhead, enveloping the audience in a dome of sound. Its like lifting the roof off your room and hearing  a plane fly overhead, the realism brings a new dimension to the movie.

Cables Needed: Same as Dolby Digital and DTS Digital.

Rapallo | Digital Codecs

DTS-ES Discrete 6.1: A true 6.1-channel format

DTS-ES optionally supports a discrete full-bandwidth surround back channel, independent from the surround left and surround right channels. This is called DTS-ES Discrete 6.1.

Instead of 5.1 channels, DTS-ES adds a sixth channel, allowing for a sixth speaker positioned directly behind the listener’s head. With DTS-ES, the speaker arrangement includes six speakers: front-left, front-right, front-center, surround-left, surround-center, surround-right, and a subwoofer.

Cables Needed: Same as Dolby Digital and DTS Digital.


Both DD and DTS use lossy data reduction techniques for soundtracks in order to minimize the limited space available on a DVD. Dolby Digital can be encoded in 192Kbps (reserved for 1.0 or 2.0 soundtracks and generally lower quality), 384Kbps (better quality), 448Kbps (used on the majority of DVD 5.1 soundtracks), and up to 640Kbps. DTS can be encoded in 754Kbps (the most commonly used), or a maximum rate of 1.5Mbps (very seldom seen). Theoretically, the less compression used in the encoding process, the better the sound quality will be. However Dolby and DTS use different compression techniques and their bit rates are not directly comparable to one another. While 448Kbps Dolby Digital encoding is better than 384Kbps Dolby Digital encoding, 754Kbps DTS Digital encoding is not necessarily better than 640Kbps Dolby Digital encoding.

Rapallo | Digital Codecs


In November 2001, Dolby Laboratories began to license the Dolby Digital EX (jointly developed by Lucasfilm’s THX division and Dolby Laboratories.) Shortly afterwards, DTS introduced DTS-ES. Both Dolby Digital EX and DTS-ES introduced a new surround back channel. However, the information in the back channel (either one or two speakers) was encoded into the surround left and surround right channels (similar to the way the center channel is encoded for Dolby Pro-Logic). The extended surround formats are fully backward compatible.

Because the surround back channel is not a discrete channel, the correct way to refer to these two formats is “Dolby Digital 5.1 EX Matrix” and “DTS 5.1 ES Matrix”. It would be misleading to refer to them as 6.1-channel or 7.1-channel formats.

Rapallo | Digital Codecs


DTS Neo:6 is equivalent to Dolby Pro Logic II and IIx. It can convert stereo and matrix content (music or movie) to 5.1 or 6.1 full-bandwidth discrete channels.

DTS Neo:6 is a surround sound processing format designed to enhance the listening experience in a home theatre environment. When playing a CD, vinyl record, or a DVD with a soundtrack that only provides two channels of information, DTS Neo:6 can expand the sound field to 6.1 channels.  Unlike DTS Digital Surround and Dolby Digital, which need to be encoded and present in the source material, DTS Neo:6 is a post-processing format. Therefore, it doesn’t need to be encoded in a specific manner so that it can be decoded to extract the correct channel assignments for the sound mix. Instead, DTS Neo:6 uses a special chip that’s built into most 5.1 or 7. 1 channel home theatre receivers to analyze all the sonic cues of a non-encoded two-channel soundtrack mixes (usually from an analog source). It then distributes the sound elements into a 6-channel home theater speaker setup as accurately as possible.

Cables Needed: Same as Dolby Digital and DTS Digital

Rapallo | Digital Codecs

DTS 96/24

DTS 96/24 is a new and enhanced version of DTS Surround and allows encoding of 5.1 channels of 24-bit, 96kHz audio on DVD-Video format. Prior to the introduction of DTS 96/24, it was only possible to deliver two channels of 24-bit, 96kHz audio on DVD-Video. It is fully backward-compatible with all DTS decoders. The DTS Encore, a new name used by DTS, simply adds more data to the old DTS formats to encode more information on the disc.

Cables Needed: Same as Dolby Digital and DTS Digital.

Rapallo | Digital Codecs


DD+ is a lossy format that uses a more efficient compression technique at data rates from 96Kbps to 6 Mbps, resulting in better sound quality. Although DD+ can support up to 7.1 discrete channels, the majority of Hollywood movies are only mixed for 5.1. Support for DD+ format is optional for Blu-Ray and mandatory for HD-DVD players. However, most movie studios prefer to use either basic Dolby Digital AC-3 or DTS Digital on their movie releases.

Cables Needed: Toslink (Optical) or Coaxial S/PDIF cannot carry a DD+ signal and will automatically play the standard Dolby Digital AC-3 track instead. HDMI cable is needed for transmission of DD+. If the player decodes DD+ to PCM, any version of HDMI connection can transmit the signal. If the player transmits the DD+ signal in bitstream, HDMI 1.3 connection is needed.

We hope that helped fill in some blanks. It was a pretty quick overview so remember expert help is a call or click away. Contact one of the Rapallo team and don’t forget, there is free lifetime tech support included with your purchase from Rapallo.

Have a great week.

Deano / Bensan / Tokorua / Simon.

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