Certainly, high-quality sound is at the heart of the THX process. In developing the criteria for THX sound, THX engineers looked at two distinct parts of a sound system:
The A-chain comprises the components that decode the sound from whatever format it is in and process that signal to remove noise. This includes the audio pickup on the projector and the cinema sound processor. Digital sound formats, such as DTS, Dolby Digital and SDDS, and noise-reduction systems, such as Dolby A and Dolby SR, are systems that improve the A-chain.
The B-chain is basically the rest of the sound system (THX crossover, power amplifiers and speakers). The THX engineers realized that no matter how good the sound coming out of the cinema processor was, a weak B-chain sound system could ruin it. To prevent this problem, THX patented a sound system design consisting of a special crossover and components from a list of THX-approved equipment. The engineers at THX subject all of the professional audio equipment on the list to a battery of tests to ensure that it meets the specifications they have established.