Receivers today offer a large number of selections for audio processing. A common question I get is what processing mode should be used. These modes are intended in general to extract information from the recording to then map it to channels that are not found in the recording, but are in your surround system. At times it may be best not to use this extra processing to create extra channels from the limited number available in the source. If the source is a match or has more channels than your system (5.1 for 5.1 for example) this type of processing should not be used. The channels in that case will be mapped to their respective speakers using logic based on the bass management and speaker topology you are employing.
Based on my own listening tests and measurements I recommend Stereo processing for music stereo (two channel) sources. Various surround music modes can be found in receivers and preamp processors. These modes in general put too much information in the surround and center channel speakers for my taste and alter the original mix considerably. I would use the subwoofer found in most surround systems because most speakers are too small to extend well to 30Hz. The only exception that I have found to this is the Studio mode found in Onkyo and Integra products. That mode is fairly subtle and may be a good option for those who own that brand of product.
Surround processing for movies, sports or other sources that include dialogue can benefit from using one of the movie modes found in your typical surround processor. These modes will redirect much of the sound found in the left and right channel to the center speaker if the recording has no center channel information. They will also put ambient sound in the surround speakers if it is a 2 channel source. Prologic IIx will also put surround sound in the back channels if is is a 5.1 source augmenting the pan. These modes can make dialog much easier to understand and add surround channels to a source that did not have those channels encoded in the source directly. I recommend Dolby Prologic IIx Movie processing for 5.1 and 7.1 surround systems. DTS:Neo6 Cinema is the recommended mode for a 6.1 surround system.
The following are my observations and measurements for some of the more common surround processing technologies.
Dolby Pro Logic II – delivers up to 7.1 channels of audio from any mono, stereo or matrix-encoded content. I did not find that this technology altered the frequency response or levels. This is the mode to use if you have a 5.1 or 7.1 surround system. The surround field that it creates is very good. It will also will focus the dialog into the center channel speaker well when the Movie option is selected.
DTS Neo:6 – delivers up to 6.1 channels of audio from any mono, stereo or matrix-encoded content. I did not find that this technology altered the frequency response or levels for the Cinema mode, but the Music Mode did. The surround field that it creates is very good. It will also will focus the dialog into the center channel speaker well when the Cinema option is selected. Best at managing the back channel in a 6.1 surround surround system. DTS Noe:6 Cinema is mode to use for movies and sports if you have a 6.1 surround system.
THX Cinema Mode – This will reduce the treble about 6 db at 20kHz. This is an attempt to implement X-Curve compensation in the receiver. In reality the X-Curve is what a room does and does not need to be added in the electronics. This should never be used.
- Circle Surround II – delivers up to 6.1 channels of audio from any mono, stereo or matrix-encoded content. This technology distorts the frequency response and alters the channel levels in both music and cinema mode options. Bass is boosted about 5db in the cinema mode and above 120Hz is reduced. In music mode the frequency distortions were more complex. I cannot recommend this mode unless you want to add more bass to two channel or Pro Logic encoded sources with dialogue.