Dolby Pro Logic II question

[zee944]

I have question about how Dolby Pro Logic II works. I'm aware of the general idea of DPLII.
It removes the lower frequencies from the front channels and puts it to the LFE channel.
It removes the identical part of the Left and Right channel and puts it to the Center channel. That's fine so far.
What I don't know: when it creates the surround channels, does it remove anything from the front channels? Or are they "redundant" in a sense?

I have seen many description of DPL II but I couldn't find out this one.

Thanks in advance.

[tebasuna51]

The Dolby Pro Logic II decoder remake the original 5.0 channels (more of less, is not a lossely operation), don't create a LFE channel with lower frequencies because this is a job for your receiver/amplifier.

Then yes, the decoder remove something from the front channels when create the surround channels, but don't remove low frequencies to LFE at all.

[zee944]

Thanks for the info. Bad news for me.

Off topic, but... is there any physical converter box that converts stereo signal to 3.0/3.1 (or 5.0/5.1 with no sound in the surround channels)? I'd like to put it between the media player and the amplifier. The point is, I want to listen stereo tracks with a separated center channel from now on. Dolby Pro Logic won't do the job as it affects surround channels too (and in a simple stereo case that would be totally fake). There are amplifiers you can turn the surround speakers on and off, but it would be tiresome to do it every time you want change from stereo to 5.1 or inversely.

[tebasuna51]

... is there any physical converter box that converts stereo signal to 3.0/3.1 (or 5.0/5.1 with no sound in the surround channels)?
I don't know for what you want this.

1) the LFE channel.
All audio equipments with a subwoofer attached can extract all low frequencies from all channels and send them to the subwoofer. You don't need extract the low frequencies to a LFE channel before. Lets do this job to your audio equipment.

2) the Center channel.
When you play a stereo all common signals in FL-FR was listened like a phantom Center channel.
Include a converter only can damage the quality. Many audio equipments have better FL-FR speakers than Center speaker (at least is recommended have better FL-FR speakers), lets play stereo audio only with Front speakers.