Anyone know what could be causing this "feathering " (time based decay problem) at higher frequencies ?

I know its not the speakers as Ive tried different types and its the same on all of them (and yes different amplifiers too) . So I guess that means it must be the measurement mic, the cable, the soundcard (motu 24ao) or the cable connecting the motu to the amp or a setting in REW or last but not least - the room - it is a very small space (caravan) let me know if you have any ideas, the ringing is most apparent on the spectogram or wterfall views. I also got a message about high distortion somewhere in the signal path - the front two speakers are slef powered genelecs and the back two are turbosound powered by an amp. The first reading is the genelec the second the turbosound (im running a surround rig - the distortion/feathering is consistent across both sets of speakers in all positions) thanks

2nd and 3rd harmonic distortion rise rapidly above 1 kHz, which doesn't look healthy. The whole shape of the IR is strange, with more and more noise at higher frequencies. Try switching to the device names that start EXCL to use the WASAPI Exclusive drivers, that should make sure everything is running at the same sample rate.

John Mulcahy said:

2nd and 3rd harmonic distortion rise rapidly above 1 kHz, which doesn't look healthy. The whole shape of the IR is strange, with more and more noise at higher frequencies. Try switching to the device names that start EXCL to use the WASAPI Exclusive drivers, that should make sure everything is running at the same sample rate.

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excellnt thast fixed it - for some reason the sample rate was set to 48 khz on the motu ad 44,1 on the ADAT (ada8000) - setting motu to 44.1 has given me sane readings - thanks for your help!!