OK, guys, I now have 2 latest version of M500s just got from Amazon and I can confirm that all M500s are fucked up in the left channel (more detail info
here). Here's the sine wave fft. The left channel perform abnormally when right channel is not playing the same audio.
Amir's test or WolfX's simply tests both channels with same audio signal so won't reveal the problem. Once the left channel input is different from the right one ( your stereo music always is), it behaves abnormally and SINAD is below 70.
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