|Originally Posted by rocko1290|
How does PLIIx know which data is the rear phantom image?
By where the energy of certain sounds are in the 2 surround channels.
Let's pretend that YOU are the PLIIx
algorithm. You have 4 surround speakers laid out in a 180 degree arc in the back half of the room. You're given 2 channels of surround information and asked to place certain sounds in the appropriate speakers. What do you do?
Imagine a sound that starts in the left surround channel and slowly moves to the right surround channel. You would move that sound through each of the 4 speakers, one by one from left to right. Think about where the sound is between the channels and it will give you a good clue about which speaker it should go to.
When the sound is only
in the left surround channel, you place it in the left side speaker. That's where you would have heard it anyway: all the way to the left. When the sound is mostly
in the left surround channel and a little bit in the right surround channel, then you start moving it to the left rear speaker. That's where it would have imaged anyway: over your left shoulder. When the sound is equally loud in both surround channels, you send it to both rear speakers. That's where it would have imaged anyway: directly behind you. And so on, as you complete the arc all the way to the right side speaker (when the sound is only in the right surround channel).
Don't think of the 2 surround channels as two discrete pools of information to be sent to only 2 speakers. Think of the surround channels as a semi-circular road map, stretching from your left side all the way around to your right side. That semi-circle can be made up of 3 speakers or 4 speakers or 40 speakers; it doesn't matter. Where ever a particular sound is between those 2 channels
will clue you in which speaker
you should send that sound to. As sounds move from one channel to the other, they will pass through the appropriate speakers in a smooth arc.
It's not complicated. Just a dumb circuit that checks voltages to see where the energy of a dominant sound is (towards the left or right). Then it just sends it to the appropriate speaker in the arc and supresses that sound in all the other speakers (using a cancelation signal). That last part helps make directionality a little more clearer and precise sounding.
|And is PLIIx a digital format?|
All the processing is done in the digital domain. But, as Ed pointed out, it's not a format. It's simply surround processing.
|What will happen if I have 6.1 channels of audio coming in and 7.1 speaker setup with and without PLIIx applied to it?|
If you don't apply PLIIx
to a 6.1 signal, then the mono surround-back channel is simply sent to both rear speakers. That information will image behind you.
If you apply PLIIx
to a 6.1 signal, then the processing ignores the discrete surround-back channel. But that's OK, since all the surround-back information is duplicated in the left & right surround channels (this is done for backwards compatibility). So PLIIx
will extract sounds for the appropriate speakers. Any sounds meant to image behind you will still be sent to both rear speakers.
The difference is with normal 6.1 decoding, the 2 rear speakers are always run as dual-mono. With PLIIx
processing, the 2 rear speakers are run as stereo. That doesn't prevent them from sometimes having the same sound for imaging directly behind the listener.