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[*]Would you consider the HD model more flexible and feature-rich, while the DL model more plug-n-play?
Being more plug-n-play certainly is not the only difference between the HD model and the DL version.
The HD model allows for bass management and an excellent parametric EQ with REW... and has a lower cost.
So why would you want to invest significantly more money in the DL version?

REW will indicate the minimum-phase filters to be used by the miniDSP processor while the DL version will use mixed-phase filters... so let's try to explain what has often been asked, what are these mixed-phase filters used by Dirac Live?

Let's consider three signals, an ideal impulse, an ideal white noise, and an ideal sine sweep.
All of them have a perfectly flat spectrum, that is, they contain an equal amount of all frequencies from DC to infinity.
The difference between them is the phase... for the impulse the phase is constant (zero unless it is shifted), for the sweep it is linear and for the white noise the phase is random.

The phase information is all the difference between these signals, and it tells us about when does each frequency arrive.
For a given frequency response the minimum phase signal/filter is the one that has the most energy arrive as early as possible (hence the name minimum phase).

Now, a speaker in a room can be measured, and showed to have some frequency response.
What we try to do with Dirac live is to improve this response in frequency (to have the desired target as in RCS) and in time (we want the impulse response to be as close to a perfect impulse as possible).

When considering only the frequency response we can (in theory) apply any filter that have the inverse frequency response and the resulting response will be flat.
This filter is often a minimum phase filter, and if the system (the speaker together with the room) was already minimum phase, the result will be a flat frequency response and the impulse response will be perfect.

If the system is not minimum phase (and this will happen at some frequencies in our normal listening rooms) the frequency response will still be flat, but the impulse response will not be ideal, (exactly how it looks will depend on the phase).
In order to get the impulse response correct for a non minimum phase system you need to use a filter that is not minimum phase.

What this filter will do is shift certain frequencies in time in such a way that they all arrive at the same time, thereby achieving the desired result... what we want to do with mixed phase filters is to move all the frequencies so that they come at the same time.

Obviously we cannot move them all to time zero, as this requires us to know about the future.... we have an advanced technology but not that advanced :) :)
Instead we shift all of them to the latest frequency, that is we delay frequencies to match the latest one (within reasonable limits of course)

An excellent document about minimum-phase is available in the REW documentation:

Ciao, Flavio
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