Originally Posted by JHAz
I'm not sure that group delan and FR are necessarily tied together. For example, the RELQ200 has almost uniform group delay, but ther is not a flat spot anywhere in its frequency response. http://www.avtalk.co.uk/showthread.php?t=10953
At least that's how it looks to me. I'd expect group delay to relate closely to phase (seems to me they're two different ways of saying the same thing).
Originally Posted by DonH50
I was under the impression Audyssey handled time and FR in which case it would correct group delay. Pioneer's MCACC does correct group delay across frequency. Hard (but not impossible) to believe a modern DSP solution would not deal with phase and group delay over frequency.
The relationship between group delay and frequency depends upon the type of filter. In a room, I can see where group delay would impact the FR by changing the nodal points, but AFAIK there's no fixed absolute general relationship between FR and group delay.
Group delay is the derivative of phase.
I am definitely not an expert on this, so I would like to know if what I posted is incorrect. This is some of what I found that I based my previous post on.
From this link
Since group delay is directly related to acoustic phase, we can actually make one further leap: group delay is
related to frequency response. The Hilbert transform is a method of deriving the acoustic phase from the
acoustic magnitude (the typical frequency response curve shown in most all literature and design programs).
There is one caveat: the Hilbert transform is valid ONLY for what is called a minimum phase system. What is
a minimum phase system? The actual way to calculate one is also beyond the scope of this paper; however,
for our purposes, a subwoofer driver operating in a box, in it's linear mode is a minimum phase system.
Operate beyond the linear limits of the driver (where distortion, power compression, suspension compression,
and other nonlinear issues come into play) and the system is no linger minimum phase, and hence cannot
use the Hilbert transform.
With the Hilbert transform, we can directly calculate the acoustic phase from the frequency response. That
is, given the acoustic magnitude frequency response of the subwoofer system, we can transform the data into
the acoustic phase frequency response, via the Hilbert transform. And, as we have seen above, we can use
the derivative of the acoustic phase to calculate the group delay. Hence, group delay is related to magnitude
frequency response for minimum phase systems (linear subwoofer systems).
I just wanted to point out that (for a minimum phase system) frequency response, phase response, and group delay response are simply three different views of the same physical 'delay' phenomenon. Change one of these responses an the other will change accordingly (remember, it's a minimum phase system).
For example, given only the frequency response of a system the phase response and group delay response can be calculated. This implies that the frequency response curve contains all the information concerning both phase and group delay. So frequency, phase and group delay are really just different takes on the same information.
I guess the big assumption is treating the sub as a minimum phase system. Most of the other links I found about this topic had math that was beyond my understanding. Looks like I have more reading to do to really understand what is going on.