You unboxed your new home theater AV receiver, ran a spool or two of speaker wire to your speakers,  hooked all your devices into your receiver, calibrated your speakers, and finally ran the last HDMI cable from your AV receiver to your TV.  Time to watch a DVD.  After the movie starts, you notice the sound is a little strange.  You look at your AV receiver and see that it is in a stereo listening mode, – only your left and right front speakers have sound.  You go to your home theater receiver’s manual, and look up listening modes.  After turning to the page for the topic, you find an assortment of AV Receiver Listening Modes available, like:  Dolby D, DTS, Dolby EX, Pro Logic II, Full Mono, Orchestra, Studio-Mix, and a lot more.  Which one do you use?  If you find this more than a little confusing, you are in good company.  Let’s make some sense out of it.

The purpose for all the AV Receiver Listening Modes is to help create an immersive experience that can transform your room into a Movie Theater or Concert Hall with stunning clarity, fidelity, and surround sound.  Of course, the listening modes only carry part of the burden for this immersive experience.  Additional variables include the type of equipment you have, how the components are connected (for example, you should have digital audio connected through fiber optic, coaxial, or HDMI cables), how they are all configured, the acoustics of your room, and the quality of your media.   Listening modes become an electronic interpretation of a Gestalt theory in psychology where the “whole” becomes greater than the “sum” of its parts.

Speaker Configuration

Some AV Receiver Listening ModesSome listening modes activate your speakers, while other modes render speakers inactive.  Knowing your speaker configuration will help you to examine the expected results from whatever listening mode you select.  The most common speaker configuration is shown below.  It is 5.1 surround sound.  This means you have left and right front speakers, a center speaker, left and right rear surround speakers (for ambient sound) and a sub woofer.  So, 5.1 surround sound means 5 speakers and a sub woofer.

Variations to 5.1 surround sound include 6.1 (a rear speaker is positioned centrally behind the listener), and 7.1 (the central rear speaker is replaced by a left and right rear speakers behind the listener).

What’s A Codec?

AV Receiver Listening Modes generally come in two flavors:

1. Standards.  Based either on a Codec (like Dolby Surround Sound) or a set of specifications (THX).
2. Enhancements (usually includes a Standard plus some pre-set audio settings in your AV receiver.  Enhanced settings usually use PCM codecs and/or Dolby Pro Logic II or DTS Neo: 6 (further explained below) with some pre-set time-phasing between the front and rear surround speakers to create the illusion of a theater or concert hall, and/or some  equalizer settings for specialized sound output.  You can find these Enhancements with names like:  Orchestra, Studio-Mix, Concert Hall, etc.)

One definition of a codec is that it is an abbreviation for coder/decoder.  This is usually a hardware driven process.  Examples are:  a signal changed from analog to digital (ADC), or a signal changed from digital to audio (DAC).  Another codec abbreviation is for compressor/decompressor.   In this version, a digital file is compressed by software, and decompressed by either software or hardware.  For example:  The DVD in your DVD player has compressed audio/video files within it, and your DVD player has hardware (chips) that decompress the file(s).

Codecs can be compressed two ways:  lossy and lossless.  Lossy compression removes data from the original file, making the file smaller, which also might have adverse effects on quality.  Lossless compression does not remove data from the file, rather it rewrites the data of the file making it more efficient.  Dolby Digital is a lossy compression, whereas Dolby TrueHD is an example of lossless compression.

Common Standards

Dolby Digital.  Also known as AC-3, is an industry standard codec used in DVDs and HDTV broadcasts in the U.S.  Dolby’s compression process (called perceptual encoding) identifies important parts of the sound track (what you can hear) and redundant sounds (that are eliminated).  Lossy compression. Provides for 5.1 surround sound, and automatically down converts for two channel systems if not supported by hardware.

Dolby Digital Ex.  Provides and extra center surround channel for up to 7.1 channels.  This  usually accommodates for a rear center speaker, or two rear speakers, but these rear channels are not discrete, – they are feaux channels created by mixing data from the initial five channels.

Dolby Digital Plus (E-AC-3).  A  codec for Blu-ray discs, home theater, broadcast, cinema, PCs, mobile devices, and streaming.  Lossy compression.  Provides up to 7.1 channels of discrete sound. Down converts to Dolby Digital for systems that are not compatible.

Dolby Pro Logic II.  This is a process, rather than a codec, using a form of PCM (Pulse Code Modulation).  PCM is a digital representation of an analog signal.  Dolby Pro Logic II can take a stereo content (two channels) and transform it to 5.1 surround sound.  This is great for old movies recorded in stereo, stereo receivers, broadcasts in stereo, standard definition TVs, etc.

Dolby Pro Logic IIx.  Works similar to Pro Logic, but takes stereo content and 5.1 surround sound and converts it to 7.1.

Dolby Pro Logic IIz.  Works as above, but starting from either 5.1 or 7.1, and adds two additional front speakers mounted in a location directly above your front left and right speakers (9.1).  This creates both horizontal and vertical sound fields.

Dolby TrueHD.  Provides eight (7.1) full bandwidth channels.  This is a codec with lossless compression.  Can support up to 16 discrete channels.  Provides a new level of fidelity.

DTS (Now called Datasat Digital Sound) is a competitor of Dolby Digital.  Its basic codec provides 5.1 surround support, with lossy compression, but without the perceptual encoding of Dolby.  Though there are a number of variants for DTS, I will mention only those common to home theater  AV receivers here.

DTS-ES Discrete.  Use this for media with DTS-ES Discrete soundtracks.  A discrete surround back channel is used for 6.1/7.1 playback.  There are 7 totally separate audio channels.  To take full benefit of the encoding, AV receivers must have DTS compatible hardware. Use with DVDs bearing the DTS-ES logo.

DTS-ES Matrix.  Similar to Dolby’s EX codec in that a sixth channel is created from a mixture of signals from other channels.  Supporting receivers have DTS compatible hardware to play DVDs with the DTS-ES logo.

DTS Neo:6.  Converts 2 channel stereo to 5.1 or 6.1.  Similar to Doby’s Pro Logic IIx, but in 7.1 mode the two rear speakers play mono.

DTS Neo:X.  Similar to Dolby Pro Logic IIz, but takes stereo, 5.1, 6.1, or 7.1 source input and outputs up to 11.1 channels (including front height and width channels).

DTS-HD High Resolution Audio & Master Audio.  DTS-HD Resolution Audio supports up to 7.1 channels, and Master Audio supports an unlimited number of channels.  Available for playback on DTS compatible hardware.  Along with Dolby TrueHD, DTS Master Audio uses loseless compression.

THX. Initially referred to a certification of performance standards met by digital audio hardware in theaters.  THX now provides post processing enhancements that take place in home theater receivers after the decoding done by Dolby or DTS.  Usually termed THX Cinema, sound output is compensated for different playback acoustics when a film was originally produced for the theater, making that output more compatible for home theater receivers. In addition, it uses timbre matching and contours the front and rear surround sound speakers to make sound output more coherent and integrated.  All that being said, most of today’s movies are remastered for home theater use, so this technology may be less relevant than it was a few years ago.

Putting It All Together

Going back to the start of this article, I gave an example of a new AV receiver being set up, firing up a DVD to play and then having sound coming from only the left and right speakers.  From the data above, we know the receiver was in the wrong listening mode.  Let’s assume for a moment that this is a 6.1 system.  Changing the listening mode on your AV receiver to Dolby Digital, will activate surround sound for 5 speakers and the sub woofer, but the center rear speaker will not be activated.  A check on the DVD case does not show that any additional sound channels were encoded (Dolby Digital Plus, Dolby TrueHD, DTS-ES Discrete, etc), so by changing the listening mode to Dolby Ex or DTS -ES Matrix, your rear speaker will be activated and included in your surround sound audio.

There you have it.  Get the popcorn, prop up your feet and enjoy your home theater experience.