CSDs and Ringing: 9/20/2017 Update Lesson 1 | Above and Beyond Simple FR: http://www.superbestaudiofriends.or...types-of-driver-ringing.65/page-2#post-162886 Lesson 2 | Cup Reverb vs. Open: http://www.superbestaudiofriends.or...types-of-driver-ringing.65/page-2#post-162951 Cumulative spectral decay (CSD) or waterfall plots measure energy content over time across all frequencies based on a "sound burst" that excites all frequencies. They are sort of like a FR over time (technically not really as they measure energy throughout the band in successively smaller windows over time.) These plots are a good tool to "see" driver ringing or resonances (seen as ridges), which typically sounds bad (piercing, glare, shoutyness, etc.); and how fast and cleanly the driver decays (speed and extraction of low level information.) For a perfect or near-perfect response, the decay should be immediate. We first see a wall (meaning all frequencies are excited) at the beginning. The next few fractions of a millisecond, the wall collapses into silence (meaning the driver is no longer vibrating or sound waves are no longer bouncing around inside the headphone enclosures.) The back wall at time = 0 is basically an uncompensated frequency response. Successive plots over time move toward us. Here is quick guide to different types of driving ringing and how bad they sound to me. Your opinions may differ. Ringing between 6kHz and 12kHz is bad. Sharp and/or thin ridges, especially those that originate from clean floors, are nasty Long duration ringing that doesn't stop by 2ms is worse than short duration ringing, which some exceptions, see  below. Rounded ridges or bumps are more benign. Ringing at 4-5kHz seems more benign than ringing below or above that range. Possibly because that frequency range tends to provide "edge." Two or more resonances which are an octave apart, sound nasty, even if they are low in magnitude or short-lived. Ringing Regions: 2-3kHz ringing: Vocal shrillness Guitar crunch Shouty 4-5kHz ringing: Adds a bit of edge, bite, and excitement to the sound. Detail (macro / coarse) 6kHz ringing: Generally tolerable, but unpleasant Similar to 5k in that it adds some bite Hardness bordering on glare 7kHz ringing: Glare with some sibilance Sharpness 8kHz ringing: Very bad. Nasty. Painful. Sibilance with some tizziness 9k-12k ringing: Adds definition More tolerable, but still unpleasant if too much Tizziness and sizzle Grainy Ringing Case Studies:  The Sharp Lower Treble Razor of Death. The sharp razor of death that occurs anywhere from 6kHz to 11kHz will almost always be nasty. A sharp stabbing sibilant sound you will get. This is seen on D7000 and LCD2r1.  The Midrange Shout. A broad ridge between 1 and 3kHz. Tends to make things sound shouty or tinny. The HP1000 has a bit of this. So do all the Grados.  Upper Mid Ridge. Usually manifests as a slightly rounded ridge at 4-5kHz. To my ears, it's the most benign type and sometimes I don't even notice it, especially if the FR doesn't have a large corresponding bump. Examples are ATH-AD2000, ATH-M50, AKG-K240, HD558, and Grado RS-1 (the issues I have with the Grado are more with the thin ridge at 8kHz than the ringing at 5kHz).  The Double or Triple Octave Penetrator. Even if the ringing is not very severe, ringing or peaks an octave apart seem especially nasty to me. Below the K601 has ringing at 3.75, 7.5 and 15kHz. That a triple penetrator. The mystery headphone below has ringing at 5k, 10k, and 20k. The resonances are not all long lived nor of high amplitude, but their effect combined together is unpleasant.