Following on from last weeks Elephant Traps in Home Cinema Setup, it got us thinking about the various audio modes that the average AV receiver is capable of decoding and generating, and that there is a generally poor understanding of what these audio modes do (or don’t do) for you. It is easy for example to find yourself listening to everything in stereo when you wanted to listen to the movie as the director intended for example in a surround format.
Most of the modern AV receivers are capable of “creating” additional channels, taking a stereo track and with some clever processing infer the extra channels from a simple stereo source. This is fine for certain system setups, however they can also down down-mix a 5.1 audio track to stereo – great if you only want a stereo output, not so good if it is unintentional. I’ve lost count of the number of times a customer has called saying the rear channels are not working, only to discover that the receiver is converting everything to stereo, or the source player is only generating stereo. In these cases a quick press of a few buttons and hey presto, back to glorious surround sound.
The sound processing is generally considered in two ways: decoding of sound formats presented from the source material, and post-processing of stereo sources.
So here is a quick summary of some of the various surround modes, what they do and when you would want to use them:
Audio Source Surround formats
These formats are generally presented by the source player and/or media you are playing. Generally most AV receivers detect the format and just get on with the decoding driving the speakers as it has been set up to.
Dolby True HD – Provides up to 7.1 full channel at 96kHz, 24bit resolution, with potentially no losses in the compression process. Data rates can be up to 18Mbps. Typically available from Blu-Ray Movies.
Dolby Digital Plus – Provides up to 7.1 discrete channels of audio with less compression than traditional Dolby Digital encoding. Data rates can be up to 6Mbps. Typically available from Downloads, DVD and Blu-Ray movies.
DTS-HD Master Audio – Provides up to 7.1 full channel at 96kHz, 24bit resolution, with potentially no losses in the compression process. Data rates can be up to 24.5Mbps. Typically available from Blu-Ray Movies.
Dolby Digital 5.1 – The most commonly used sound format for DVD video, and is also the standard for US television. Dolby Digital 5.1 sources deliver sound with five discrete full-range channels; left, centre, right, surround left, surround right, plus a low frequency effects (LFE) channel.
DTS 5.1 – Less common than the Dolby Digital format, but generally recognised within the audio industry as being of superior sound quality. DTS 5.1 delivers surround sound with five full range channels plus an LFE channel.
DTS-ES 6.1 Matrix – This is a 6.1 channel format based on DTS 5.1. It has the sixth channel matrix encoded into the surround left and surround right channels. The sixth channel is a surround centre channel and is directed to the surround back left and surround back right speakers. Available from Some DVDs and Blu-Rays.
DTS-ES 6.1 Discrete – This is a true discrete 6.1 channel sound format (unlike DTS-ES Matrix). DTS-ES discrete mode operates only on sources with DTS-ES 6.1 discrete audio encoding. Available from some DVDs and Blu-Rays.
DTS 96/24 – Provides up to 5.1 channels of audio at 96kHz, 24bit resolution for superior sound quality compared to standard DTS 5.1. Found on some DVD audio disks.
Audio Post processing (i.e. generated) sound formats
Stereo – standard CD and broadcast audio consists of stereo i.e. two channels of sound, one for left and one for right.
Dolby Pro-Logic – Dolby Pro Logic is a legacy mode that is designed to produce a five-channel output from two-channel source material. It should be used only when the source material is encoded as Dolby Pro Logic; otherwise, we recommend the use of Dolby Pro Logic II. This is because Pro Logic processing on straight stereo sources can sound muffled and compressed.
Dolby Pro Logic II – Dolby Pro Logic II decoding is designed to produce five-channel output from two-channel source material. There are three different modes available in Pro Logic II: ‘Movie’, ‘Music’ and ‘Game’ modes, which are intended for use as their names suggest. Due to the different recording methods used for movies, music and video games, it is recommended that the correct decoding mode for your source material is used to obtain best results.
Dolby Pro Logic II Movie -This is intended for ‘cinematic’ material, which is mixed and monitored in a calibrated multichannel environment. Movie mode is a ‘fixed’ mode that is designed to give a similar sound when listening using a home cinema system to that obtained in a cinema.
Dolby Pro Logic II Music – This is intended for surround processing, although good surround effects can be obtained through careful production. As the optimum decoding method varies according to the recording, Music mode often allows the user adjustment of the processing characteristics.
Dolby Pro Logic II Game – Video games today are extremely sophisticated, with dramatic 5.1 surround audio tracks. Game mode gives augmented bass management to capture the full effect of game sounds panned to the surrounds, ensuring the bass impact from purer surround effects are fully delivered to the subwoofer.
Dolby Pro logic IIx – Used for 7.1 system setups, this is an extension of the Dolby Pro Logic matrix-decoding method. The decoder allows the processor to derive seven outputs from a two or multichannel (up to 5.1 with EX) source to take better advantage of all amplifiers and speakers in a 7.1 setup. As with Pro Logic, there are three different modes available: Movie, Music and Game. Due to different recording methods used for movies and music, you should select the correct mode for your source material.
DTS Neo:6 – provides up to six full-band channels of decoding from stereo material. The AV receiver / processor will derive separate channels corresponding to the standard home theatre layout. As for Dolby PL II there are a number of alternatives:
DTS Neo:6 Music – A music mode designed to produce a lively high-integrity surround-effect from most two-channel music sources from all available speakers. Neo:6 music mode attempts to expand stereo recordings into the five or six-channel layout without diminishing the subtlety and integrity of the original stereo recording.
DTS Neo:6 Cinema – This is a mode designed to reproduce a movie theatre environment. Neo:6 technology allows various sound elements within a channel or channels to be steered separately by the user, and in a way which follows the original presentation naturally.
All Channel Stereo – This takes the stereo signal and sends left or right channel information to the other channels available. This is usually used if you want to have background music playing, with no particular focus.
DTS 5.1 Stereo Downmix – This takes a 5.1 format source material and mixes it down as it suggests into stereo. This is usually used for example for listening via headphones.
You might select a post processing audio mode (e.g. Dolby PLII or DTS Neo:6) for installations where there is a 5.1 or greater speaker setup, and in particular if there is a small screen (i.e. TV) and the left and right speakers are some way from it. In this case the standard stereo channels can become disjointed from the picture: Applying one of the surround processing modes, allows the centre channel information (typically the speech) to be generated from the centre channel speaker, bringing the focus back to the screen. If the left and right channel speakers are close together either side of a small screen, in our opinion there is little to be gained by one of the post processing surround modes.