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I have an ausio remote cable, but it is not Sony, and maybe there is something in that unit that is not allowing the mic signal to get through.
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I think that is the problem. Quoting from somewhere else:
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It has been brought to my attention that some of the "knock off" PSP remotes do NOT support the microphone function for the PSP. This is true regardless of the type of headsets used (Official Sony PSP headsets or PC headsets plus this adapter). After I obtained one such remote (Thanks to a very generous ebayer!), I checked its internal components and found the counterfeit remote uses the 3C female connector instead of the needed 4C type. The microphone contact is simply NOT THERE!!
I cannot tell you what kind of remote will not work because 1) I only use the official Sony PSP remote and 2) the counterfeits look all alike from the outside! I can tell you though, if you use the official Sony PSP Remote, THIS ADAPTER WILL WORK! (of course, assuming you have the correct Sound Blaster Compatible PC headset).
If that´s the case you won´t be able to use the microphone with the SOCOM game for on-line play either.
SOLUTION: Get an official one (or a 2nd hand one) . Avoid counterfeits of eBay.