The listening modes available vary from Onkyo receiver to receiver. Some support THX, some don't, and those that do support different levels of THX. The listening modes are also dependent on the signal type (DD, DTS, multichannel pcm, TrueHD etc.), and your speaker configuration. That's why it's important to configure your speakers correctly. For instance PLIIx should only be available if you have 7.1. If you have 5.1 and correctly disable the surround back speakers, PLIIx disappears as an available choice.
For ease of understanding, I divide the listening modes up into a few categories. The first category includes all the listening modes with a name the same as the signal type it's intended to support. Call these the standard modes. Each of the following signal types has a standard mode: Dolby Digital, Dolby EX, Dolby Digital+, Dolby TrueHD, DTS, DTS 96/24, DTS ES Discrete, DTS ES Matrix, DTS HD High Resolution, DTS HD MA and multichannel PCM.
You can select a standard listening mode if and only if you're receiving the associated signal type. For instance, you can only select the TrueHD listening mode if you're receiving a TrueHD signal. You can only select the DTS listening mode if you're receiving a DTS signal. If you can't select the TrueHD listening mode, then you're not receiving a TrueHD signal, no matter what you selected on your player. Clearly it's important to know what kind of signal you're receiving when working with listening modes. It's important to know both the encoding such as DD, DTS etc., and also the number of channels present. Is it DD 2.0 or DD 5.1? Is it TrueHD 5.1 or TrueHD 7.1. On Onkyo's, you determine the signal type by pressing the Display button one or more times. Learn how to tell what signal type you're receiving. It will answer a lot of questions for you.
When you select a standard mode, you're not telling your receiver how to decode the signal. It does that automatically as all receivers do. So what does it mean to select the Dolby Digital listening mode when receiving a Dolby Digital signal? It means, do everything in a standard manner according to all the other sound settings you've set. In other words:
- Apply bass management
- Apply tone control settings
- Apply equalization
- Don't increase or descrease the number of channels present in the signal
The second category includes all the modes that matrix incoming signals. When you select a matrixing mode, you're implicitly selecting the standard mode for the signal type you're receiving then applying the matrixing on top of that. Matrixing outputs sound to more speakers than the number of channels that were included in the original signal. Typically matrixing modes are used to convert 2 channel input signals to 5 channel or 7 channel output, 5 channel input signals to 7 channel outputs, or 5 channel inputs to 6 channel outputs. The matrixing modes are PLII, PLIIx, Neural THX, DTS Neo:6 and Dolby EX. THX Select 2 and THX Ultra 2 also perform matrixing and are discussed in the THX section.
You should experiment with all the matrixing modes, but the most commonly used and recommended matrixing modes are Dolby Pro Logic II and Dolby Pro Logic IIx - PLII and PLIIx. PLII was invented as an upgrade to Dolby Pro Logic which was the original home theater sound standard. Early home theater systems included multiple speakers, but prior to the invention of Dolby Digital had to make do with 2 channel sources. Dolby invented a way of embedding surround information in a 2 channel source that could be extracted using the Dolby Surround processor in a home theater receiver. Most VHS tapes were encoded with Dolby Surround as were many broadcast television shows. PLII is a more recent and very much improved version of Pro Logic. PLIIx includes everything that PLII does and extends the capabilities to matrix to 7 channels instead of just 5.
PLII/x can synthesize surround information from any source, but you won't get much surround information from movie and television sources that aren't encoded with Dolby Surround technology. Note that PLII and PLIIx have separate modes optimized for movies and music. You can try either mode for either type of material but Dolby optimized each for the intended source.
The third category are the Onkyo DSP modes like TV Logic, Orchestra, Unplugged etc. AFAIK, these are legacy modes that predated the creation of all the digital signals and corresponding standard modes that are now available. You may find that you like them, but they were probably included primarily for users upgrading from older Onkyo receivers. The most popular Onkyo DSP mode is All Ch Stereo which is often used with music sources in a party environment. It provides approximately equal volume from all the speakers. The sound is not realistic, but for a lot of people it's still a guilty pleasure.
The fourth category are the THX modes including THX Cinema, THX Select 2, and THX Ultra2. All of these modes start with standard mode processing then apply a set of THX invented signal processing algorithms that THX claims makes the sound more in line with what the movie producers wanted you to hear. These techniques include Re-EQ, timbre matching and adaptive decorrelation. You can read about what they do on THX's website. THX Select 2 and THX Ultra 2 combine the THX effects with 5 channel to 7 channel matrixing. If the original signal wasn't already 5 channel, the THX modes will use either PLII or Neo:6 to matrix it to 5 channel before applying the other processing.
The fifth category consists of the Direct and Pure Audio listening modes. These modes disable much of the digital processing that occurs when you use one of the standard modes. Bass management is turned off, which means any crossovers you set in the Speaker Config are ignored. The only sound sent to the subwoofer is the LFE (.1) channel. For stereo sources like CD's, your subwoofer will not be used at all. The Direct and Pure Audio modes also disable the equalizer settings set by Audyssey and any tone control settings. There may be other changes as well, but you get the idea. Direct and Pure Audio attempt to play what's on the source with very little processing. These 2 modes are more popular for use with music than with movies. Try these modes with movies, but unless you have full range speakers, especially your front 3, you'll notice a lot less bass than you will with one of the standard or matrixing modes. That is, as long as your front speakers aren't set to Full Range.
The final mode, in a category of its own, is Stereo. Stereo can be thought of as the standard mode for 2 channel sources. However it also has the ability to take any multichannel source and downmix it to 2 channels.