The burst responses follow up with thd on good systems. But there are lots of bad systems where they just don't correlate. Happy to hear the raal is one of those good systems. I personally own thx00 and I know the list of aberrations it produces which go unnoticed in FR and thd charts. I have a full on explanation of why thx00 has a sibilance with male vocals even though it's thd and fr says opposite. I have test tones which can measure the same, I'm currently writing out equations which describe the same. Also thanks for the measurement advice, using an electret in the ear and measuring. I have to try the same for my srh1540 and if I could find, a srh1840. They seem to measure bad in thd but in reality it's actually the measurement rig rattling. That kind of thd is quite impossible mechanically considering their Csd is among the quickest.