Hello Quadranarians,
Sorry I have not been here the last few days. I managed to get a terrific dose of the Rhino Virus. I, however, feeling better, think it is time for the "SOAP BOX".
Old Quad Guy, The information theorem is one of my favorite discussion subjects. It states that for a given number of input channels, there must be the same number of transmission channels, to reproduce to the same of output channels. This is then defined by 3 numbers. Take Discrete Quad for example. It is defined as 4-4-4, 4 input channels, 4 transmission channels, 4 output channels. It fulfills the Information Theorem perfectly. Now what about any of the matrix systems. These systems have 4 input channels, 2 transmission channels, and four output channels. They fail the Information
Theorem even with all the processors. This is because the 4-2-4 systems are all 2 channel stereo with 4 inputs and 4 speakers.
Here is an analog that should demonstrate what a matrix 4-2-4 system does. Imagine four soda glasses, each one half filled with a different soda. Glass 1 has orange soda, glass 2 has root beer, glass 3 has cherry soda and glass 4 has lemon soda. These are the 4 input channels with the color of the soda equivalent to the phase shift. Now imagine 2 empty glasses representing the 2 transmission channels. Now take input glass1 and input glass2 and empty the contents into transmission channel glass 1. Then take input glass3 and input glass4 and empty these contents into transmission channel glass 2.
Now here is the problem, having poured the orange and the root beer into the same glass, regardless of color, how do you separate them back into their original discrete soda form? The answer is you can not!! All the 4-2-4 matrix systems do is to mix (add) 2 signals on the left together and put them on the left channel and they do the same for the right channel. Phase shifting at audio frequencies serves no purpose unless you are using it as a "guitar effect".
Wait a minute, what about , Tate, Prologic etc.? Well these devices have an interesting effect. When the Information Theorem is satisfied, they can do something that appears to be correct. When the Information Theorem is not satisfied, they become quite confused. There are 2 conditions in matrix 4-2-4 where the Information theorem is satisfied. Condition number 1 is sending only 1 of the 4 channel at a time. The example is LF only with LB,RF,RB silent. In this case the Tate, Prologic,etc processors have enough information to turn the level down on LB,RF,RB and leave the level up on LF. If only one channel is sent at a time, the sound can be made to appear going around the room. Quadraphonic right? No, it is only a special effect! The minute there are more then 2 audio channels being sent, all bets are off. By the way, when all 4 channels are input on a 4-2-4 matrix system, there will be at least 1 pair of channels on the output that will have no more than 3dB of separation.
I know there are a lot of you out there with large libraries of SQ and QS records. I also know that some of these synthesized Quad records can sound interesting. I recommend that you enjoy them, but remember they are synthesized and not true Quad as is discrete Quad.
The answer to your Questions Old Quad Guy, no it will never be possible to decode 100% of a QS or SQ recording because there really was nothing encoded! Contrary to popular opinion, the Tate unit was not very complex and could be easily duplicated.
Quadfather, Good thoughts, and remember TAAS.
Lou Dorren
