CFD Online Discussion Forums - Unclear points in using "libAcoustics"

Hi, Foamers.

I'm trying to use libAcoustics to calculate sound from fan.
I can get some result by using the library, but some unclear points remain, so I hope I could get any helpful information.

①
What are "patches" "surfaces"?

When I try to use the library in type of "Curle", entry "patches" is required and I think this is the surface where pressure is integrated.
Then, what is the entry "surfaces" in type of "Ffowcs～"?

②
What is the entry "fixedResponseDelay" "responseDelay"?
I think this is related to "retarded time" of aeroacoustics.
And I think when the entry "fixedResponseDelay" is true, "responseDelay" is needed.
So, what happens when "fixedResponseDelay" is false? Retarded time is set to each surface?
And how is the "responseDelay" used? Is the data from "responseDelay" ago used to calculate the sound pressure for all observers?

③
When this library is used in postProcess, the time of result is strange like this.

Quote:

Time a_pFluct b_pFluct c_pFluct d_pFluct e_pFluct f_pFluct g_pFluct h_pFluct i_pFluct j_pFluct k_pFluct
-0.2 0 0 0 0 0 0 0 0 0 0 0
-0.1999 583.926 1257.97 1325.29 992.467 494.546 35.7653 -357.821 -633.861 583.926 -931.421 6.83326
-0.1998 1513.1 1583.35 1409.5 1087.07 694.364 287.631 -95.187 -431.394 1513.1 -898.753 7.53355
-0.1997 1511.08 1582.91 1409.22 1086.58 693.753 286.91 -96.1366 -432.313 1511.08 -899.07 7.49675
-0.1996 1511.16 1583.09 1409.45 1086.95 694.125 287.209 -95.8915 -432.101 1511.16 -898.842 7.52446
-0.1995 1511.08 1582.98 1409.33 1086.68 693.827 286.95 -96.1191 -432.3 1511.08 -899.065 7.50776
-0.1994 1511.32 1583.28 1409.63 1087.12 694.264 287.308 -95.8543 -432.13 1511.32 -898.989 7.53715
-0.1993 1511.17 1583.02 1409.38 1086.86 694.059 287.194 -95.8779 -432.089 1511.17 -898.904 7.5192
-0.1992 1511.1 1583.06 1409.46 1086.91 694.08 287.176 -95.9302 -432.152 1511.1 -898.96 7.52179
-0.1991 1511.2 1583.15 1409.51 1086.97 694.128 287.205 -95.9084 -432.137 1511.2 -898.949 7.52491
-0.199 1511.15 1583.01 1409.36 1086.84 694.024 287.141 -95.9245 -432.113 1511.15 -898.867 7.51607
-0.1989 1511.04 1582.88 1409.23 1086.68 693.884 287.034 -96.0034 -432.163 1511.04 -898.873 7.50794
-0.1988 1511.1 1583.1 1409.48 1086.83 693.958 287.044 -96.066 -432.273 1511.1 -899.041 7.51802
-0.1987 1511.42 1583.42 1409.79 1087.23 694.345 287.36 -95.8416 -432.151 1511.42 -899.073 7.54385
-0.1986 1511.35 1583.25 1409.62 1087.11 694.272 287.335 -95.7971 -432.06 1511.35 -898.95 7.533
-0.1985 1511.07 1582.84 1409.19 1086.76 694.015 287.182 -95.8425 -432.014 1511.07 -898.761 7.51023
-0.1984 1510.74 1582.55 1408.93 1086.44 693.728 286.985 -95.9623 -432.051 1510.74 -898.668 7.4921
-0.1983 1510.68 1582.6 1409.04 1086.6 693.892 287.112 -95.8808 -432 1510.68 -898.65 7.50816

The time strangely starts from -0.2. What does this mean and why does this happen?

I'm sorry to make many questions once, but any little information would be helpful.

Kosuke