Circle Surround - What It Is and How It Works

Circle Surround Diagram


If you own an older sound bar, HDTV, or home theater receiver, you may notice a setting on the audio setting menu labeled "Circle Surround" - but what is it exactly?

Long before the Dolby Atmos, and DTS:X surround sound formats, a company known as SRS Labs was working on ways to create a surround sound format that was more immersive than the Dolby and DTS formats available at the time.

At the time of its development, Circle Surround approached surround sound in a unique way. While Dolby Digital/Dolby TrueHD and DTS Digital Surround/DTS-HD Master Audio approach surround sound from a precise directional standpoint (specific sounds emanating from specific speakers), Circle Surround emphasizes sound immersion.

How Circle Surround Works

To accomplish this, a normal 5.1 audio source is encoded down to two channels, then re-decoded back into 5.1 channels and redistributed back to the 5 speakers (front left, center, front right, left surround, right surround, plus the subwoofer) in such a way as to create a more immersive sound without losing the directionality of the original 5.1 channel source material. Also, Circle Surround can also expand two channel source material into a full 5.1 channel surround sound listening experience.

Circle Surround Applications

In addition, it is also possible for music and movie sound engineers to actually encode content in the Circle Surround format, and if the playback device (TV, sound bar, home theater receiver) has a Circle Surround decoder, a listener can actually experience a somewhat immersive surround sound effect that is different from what you would experience from straight Dolby Digital or DTS based formats.

For example, there are a number of audio CDs that have been encoded in Circle Surround. These CDs can be played on any CD player, with the Circle Surround-encoded passed through the player's analog stereo outputs and then decoded by a home theater receiver that has a built-in Circle Surround decoder. If the home theater receiver does not have the proper decoder, the listener is still able to hear the standard stereo CD sound.

The most recent incarnation of Circle Surround (2001) is referred to as Circle Surround II, which expands the original Circle Surround listening environment from five to six channels (front left, center, front right, left surround, center back, right surround, plus the subwoofer), and also adds the following:

  • Improved Dialog Clarity and localization.
  • Bass Enhancement
  • Full frequency range for all channels.
  • Improved channel separation.

More Info

Examples of past products that have included either Circle Surround or Circle Surround II processing include:

  • Marantz SR7300ose AV Receiver (2003)
  • Vizio S4251w-B4 5.1 Channel Sound Bar Home Theater System (2013)
  • Circle Surround-encoded CDs

Related Surround Sound technologies originally developed by SRS and transferred to DTS include TruSurround and TruSurround XT. These audio processing formats have the ability to receiver multi-channel surround sound sources, such as Dolby Digital 5.1 and recreate a surround sound listing experience using just two speakers.

Since the takeover of SRS Labs by DTS in 2012, DTS has taken the elements of Circle Surround and Circle Surround II and incorporated them into DTS Studio Sound and Studio Sound II.

DTS Studio Sound adds features such as Volume Leveling, for smoother transitions between sources and when changing TV channels, bass enhancement which improves bass from smaller speakers, Speaker EQ for more precise speaker level control, and Dialog Enhancement.

DTS Studio Sound II expands virtual surround sound flexibility further with improved directional accuracy, as well as more precise bass enhancement. Studio Sound II also incorporates a multi-channel version of DTS TruVolume (formerly SRS TruVolume) which provides better control of volume fluctuations both within content and between sources.

DTS Studio Sound II can be integrated into both home (TVs, soundbars), PCs/Laptops, and Mobile Devices.

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