Will add-on height channel decoders ever emerge?
Sound & Vision reader Lee Carroll brings up a great point that I completely overlooked in my two articles about Dolby Pro Logic IIz height channel technology. Having recently bought a new receiver, Lee asks, "Don't the merits of this new technology just scream for some interim gear that will only decode the high speakers? Then those of us with 5.1 systems can have this new technology."
I, too, recently bought a new receiver, and would love to have an aftermarket height channel decoder. However, I think it's unlikely that anyone will create a dedicated decoder for height channels in the same way that some companies made add-on boxes for Surround EX back in 2000.
Unless I'm completely missing something, creating an aftermarket height channel decoder would be complicated. A manufacturer could make a box that would take digital input and output analog 5.1 + height, which you'd then connect to your receiver's 7.1 analog input. Or they could make something that goes between a surround processor and an amplifier, that would take analog line in, digitize it, do a PLIIz decode, then convert it back to analog and output it to the amp. But for what it'd cost to develop and build such products, and the small quantities they'd be likely to sell, both would probably cost more than the least expensive PLIIz receivers.
That's not to say someone won't "phony-up" an aftermarket height-channel decoder. There's no standard for what's supposed to come out of those channels. Here's the first thing I'd try: Take the left, right, left surround and right surround line outputs from a surround processor, combine them, filter out everything below 3 kHz or so, reduce it in level by about 12 dB, then feed it out to the height-channel amps and speakers. This is far simpler than the process used in PLIIz or in Audyssey's DSX technology, but it might sound OK nonetheless. I tried something similar to this scheme once using a Parasound surround processor that allowed custom blending and filtering of channels.
Given that PLIIz products hit the market only a few weeks ago, it's way too soon to predict how all of this height-channel stuff will evolve, and which, if any, technologies will prove successful.