Audio formats for the General Public


"A little reminder: One should firstly look at the difference between rear Surround speakers and lateral Surround speakers. Until now, there were two schools of thought regarding the utilisation and placing of Surround speakers. Some, anxious to retain musical coherence, advocate the utilisation of classic speakers, more or less identical to the main speakers and positioned in the two rear corners of the room. Others, following the example of THX, prefer to optimise the "cinema" aspect, suggesting the utilisation of Dipolar type Surround speakers situated laterally, with the listener sitting in the centre of the axis on which they are placed.

The EX signal is not, strictly speaking, the result of encoding. It is the sole channel resulting from the mono combination of the two rear channels of a 5.1 signal whether it be Dolby Digital or DTS. It’s exactly the same mixing procedure that was used in the good old days of Dolby Surround ProLogic to create the central channel. At the time, the right and left channels were used to mix the central channel. In the current case, the right and left Surround channels are used to mix a central rear channel. The decoder will then detect and filter all identical information it finds in the two Surround channels, take it out, and then send it to a separate central channel.

The Surround EX system was jointly developed by the Dolby laboratories and THX, who jointly hold the licence for this standard whose exact name is THX Surround EX. The name used on programmes, in this case on DVD’s, is not yet determined. This consequently implies that, in order to operate properly, any machine using the system should, in the first instance, utilise the Dolby procedure for filtering and extraction on the central channel to, in the second instance, obtain full the benefit of THX, including "Timbre Matching" and the "Dynamic Deccorrelation Filter" the lateral Surround speakers, as well as the "Re-Equalisation" of the central rear channel.

Conclusion: Yamaha not being partisan to THX (as they have their own DSP system to re-create a cinema atmosphere), the brand has consequently seen itself prohibited from using the EX trademark and only has the right to use denominations reserved for non-labelled apparatus, nevertheless effectuating the filtering and extraction of the central Surround channel: Dolby Digital/Matrix 6.1. In addition, even if Yamaha effectuates its own work on the EX channel with the aid of extremely powerful DSP’s, they still don’t use the THX procedure and are thus deprived of the mention "EX".

This rule is pitiful in forcing manufacturers to join two labels – and thus to pay two times – plus something that remains a simple commercial argument: in this instance, a logo. The EX brand, however, represents important "value added" of which Yamaha is deprived, due to the simple fact of their difference. All the same, the Yamaha brand has become a master in the art of sound processing and handles the subject probably as well, if not better that THX.

What about DTS?
For DTS, the situation is identical to that of THX Surround EX with regard to the mixing of the rear central channel. It is indeed a veritable mixing of a supplementary channel in the two Surround channels we’re dealing with. And while DTS has still not, to this day (January 30th, 2000) delivered specifications concerning the filtering and extraction of this rear central channel, it could well be the most intelligent path to take, consisting of leaving each manufacturer to their own devices. Effectively, as we mentioned above, the filtering and extraction of this channel result from the same kind of procedures as those utilised over the years to create the central channel of Dolby Surround ProLogic. This procedure being perfectly mastered by all manufacturers, it is thus perhaps not indispensable to edit a special technical specification sheet which would only be a word for word reproduction of that published ten years ago by Dolby. As a result, when a manufacturer uses a Dolby decoding chip, it should be DTS ES, (ES : Extended Surround) compatible. The term "compatible" nevertheless remains necessary, because the machines will only really be DTS ES the day DTS edits a real set of technical spec.’s.
Thus, for the moment, no DTS ES machine exists… only "DTS ES compatible" machines."

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