Tucci: Where is the line between minimum phase and non-minimum phase?

John: Good question! It reaches that murky gray area at fractional-space loading for me. This is because a reflection is a time issue and non-minimum phase, yet we EQ fractional-space loading and it is a very short (in terms of the wavelength of interest) reflection.

John (continued): Those that truly understand it speak in terms of S-planes and poles and zeros – and I don’t want to go there. However, there is some detection of that with the coherence thing in SMAART and SIMM and some older TEF software too. Just know that time is a different problem and it takes digital] delay, or FIR (DSP) filtering to address it, and propagation delay is the price for FIR filtering.

Tucci: Does an analog transversal EQ have propagation delay? How about in the electrical domain? Where is that dividing line?

John: I don't know for sure, but I would think it would have to. And I do know that the old IRP did work using delay taps, so I think, yes transversal EQ’s have propogation delay. I don't think we have the same problems in the electrical world because a circuit node is a single point for typical sound systems. However, for teleconferencing systems, when they deal with echo cancellation, they must use FIR filters for the time issues.

Moderator: This will be our last question for the evening.

keith: What's the latest from TOA in DSP these days? Any interesting applications (in the field) of this that you've noted?

John: The current DSP, the DP-0206, has an interesting feature. It can import TEF or SMAART files, including all the magnitude, frequency, and phase/group delay/time information into the software. This enables the user to load in one TEF sweep or SMAART file per raw driver and then, off-line, you can tune the speaker system, say on the way to the job site. I've tried it, to make sure it really works. And it does. It’s something I think we'll see other manufacturers begin to emulate soon.

keith: Thanks, John, for sharing your time and information! And thanks to our moderator, Another Dave, Mr. Dermont. A transcript of tonight's chat will be available for viewing on PSW.

John: Thanks guys, have a good evening...

keith: Be sure to join us next week, May 29, for a chat session with Joe Wisler of Ashly, formerly of Crown and possessing a lot of knowledge and experience. And, continue the chat on PSW forums like live audio board.