Hi John: I use REW generator 5K,10,15,20K HZ and play with my Macbook. meanwhile I record with RTA and the plot are as attached. The peak at individual frequency have similar dB( see attached). Then I copy each frequency wav files to my pocket SSD and play them by Cambridge 851N network player + burmester ampifier+monitor audio gold 300 speakers. The RTA plots show great different. It may be the reason why my REW file always roll-off the high frequency section?