You folks have quite some ears. The best I got for the title test a few hours ago was -48 dB with an EQed Meze Elite (
which I had already measured as having exceptional multi-tone distortion; looking at FFTs of the Klippel test signal, it seems like BI multi-tone distortion is the closest in character to the kind I've been measuring out of headphones). I had previously scored -42 dB (sidebands around 44 dB below the fundamental per my FFT analyses). Somewhat surprisingly, putting my desktop to sleep to silence the fans and instead connecting my cellphone to my FiiO K9 Pro ESS for unEQed listening had me scoring only -39 dB. I can hear the harmonics or subtle "warbles", but they eventually just disappear or get masked and I end up hearing the same artifacts or "placebo" for each. For curiosity, I used Equalizer APO to apply notch filters (whether or not any of the folks who made it to -69 dB used this trick or looked at the FFTs among other exploits) which allowed me to get to -63 dB, my needing to apply yet deeper peaking filters to be able to discern -69 dB (sidebands 71 dB below the fundamental, or around 0.03% THD, my FFT showing around an 81 dB SINAD for the undistorted signal; with the -100 dB 999 Q peaking filters, the upper tone's sidebands were instead 23 dB below the fundamental, almost at the -120 dBFS noise or distortion floor of my MOTU M2 loopback as seen on the REW RTA), the volume in both cases rendering the recording's noise floor audible.
For ""6 inch driver" playing "octave - multitone - Bl only"", I scored -21 dB (though I was technically guessing by -18 dB which per the FFT had the sidebands around 34 dB below the fundamental). On my REW RTA FFT through the MOTU M2 loopback with 128k length and Blackman-Harris 7 window, this recording consistently already had some sidebands around 58 dB below the fundamental, whereby the -36 dB distortion level was almost indistinguishable in the FFT, -42 dB looking properly indistinguishable, however folks could have gotten to that level or the -45 dB maximum without exploits.
Otherwise, for the ""full range speaker" playing "Music T. Chapman"" test, I swear the recording is so poor that by -15 dB, the added distortion is indistinguishable. I don't know if there were any tells or exploits that have since been fixed, as I'm hearing the same decays, artifacts, or subtle inflections in both by that level with all distortion buffeting having disappeared.
Now, I do unfortunately have high-frequency tinnitus and have been attending lots of classical symphonic concerts, but since my first encounters with sine sweeps, I would swear that even when I measure harmonic distortion well below what should be audible, I hear spurious tones being excited in addition to the actual perceivable fundamental suggesting either my own ears distorting or my cochlea having spurious excitations, perhaps further masking the harmonics I should be looking for. E.g. If I play an 800 Hz pure tone that certainly doesn't have digital distortions above the FFT noise floor, I also hear a 930 Hz resonance at least with the left ear, maybe a different frequency for the right ear, said resonance being proportional to the fundamental's loudness and for my moderate to loud listening starting to just become audible at as low as 170 Hz. But once I get up to 930 Hz, I start hearing a 1,080 Hz phantom resonance or something, and so on. I haven't read into whether and to what extent different individuals' ear physiologies may distort audio to different levels or whether some individuals actually have sharper spectral filtering.
Of course I am still able to have blissful musical experiences, but I can't help but wonder how life would be without this probably primarily fire-alarm-induced tinnitus and these weird single-tone resonances.
” Denney
