Youtube video review: http://youtu.be/sTmWZmVAjGs Note: This review applies to the t-Jays Four IEM when used with the Jays Curves (Dirac HD) music player, except as noted below when comparing the sound with the Dirac DSP (Digital Signal Processor) turned on or off. This app works with the i-device headphone jack obviously, but also works with the LOD (Line Out Dock) to an analog headphone amp. Both the 30-pin and Lightning connectors work (Lightning if you have an adapter), and while there's an obvious difference in sound with an amp compared to the i-device alone, this app is tuned for the headphone jack, so using a headphone amp from the LOD might change the sound in a way that the DSP is not optimized for. Review summary: The Jays Curves music player for Apple i-devices that use 'apps' will make the t-Jays Four sound about as good as any headphone I've heard, in terms of frequency response at least, if not other parameters as well. The limitations in using the Jays Curves player are: It works only with devices that support this player, maximum volume is reduced compared to using the t-Jays Four with the standard (built-in) music player, and the Dirac sound treatment applies only to the Jays Curves music player - not to videos, Web sounds, or any other audio facility of the device. Dirac uses (among other things) what is probably very high quality parametric equalization to smooth out the sound of the headphone, when using the Jays Curves app. I installed the app on my iPad, iPhone, and iPod Touch, and it does the same things as the built-in music player, using the same music track lists. The appearance of this Jays Curves app represents a breakthrough in personal high fidelity, from my point of view. Until the Dirac music player appeared for Apple Earpods and earbuds a couple weeks ago, headphones were generally played without special sonic treatments, except for EQ applied by users, or "soundstage" enhancers provided with certain headphone amps. To my knowledge, the Dirac app for Earpods (and now for the t-Jays Four) enabled headphone users to take advantage of DSP for the first time, to clean up the impulse (time-based) response of their headphones. Without the Jays Curves app, the t-Jays Four is very bassy and bright, having what headphone users typically refer to as a 'U'-shaped response. The Jays Curves app flattens that out pretty well, but in fixing the impulse response too, it goes well beyond EQ (even perfect EQ), to create a clarity of sound that you would never expect to hear anywhere near this price point. The hi-fi breakthrough I referred to above is having the Dirac DSP for a "real" earphone rather than the $29 Apple Earpods. While the Earpods with DSP equal or exceed the sound quality of some pricy headphones in certain ways, they just don't have the ultimate resolution of audiophile headphones and IEM's. Comparing the Earpods/DSP signature to the t-Jays Four, the Earpods' bass is slightly boomy, and the midrange sounds lighter or very slightly more nasal. The t-Jays Four also extends and improves the highs in a way that makes high-frequency instruments like triangles and bells sound better (see the Jennifer Warnes track below), and those improvements create a better sense of space or soundstage as well. Some of the music tracks I've played are 320k CBR MP3's I converted from high-resolution downloads, from Chesky, HDTracks, Blue Coast, etc. One such track, David Chesky/Wonjung Kim - Girl From Guatemala, sounds as good as I've ever heard it - full dynamics, no distortion - extremely smooth. The Shure 1840 headphone has my favorite treble, but most of the others I have are treble-shy. The Sennheiser Momentum and ATH ESW9a have a recess of about 5 db in the main brightness or "presence" area, the B&W P5 is recessed about 3 db, and the v-moda M80 about 6 db. The t-Jays Four/Curves treble is much closer in sound to the Shure 1840 than to the next most accurate headphone, the ATH ESW9a. The Curves app not only gets the amount of bass and treble right, but smooth enough that I'm not experiencing irritations with sibilants or low-quality music tracks. EQ-related tweaks generally have negative connotations for audiophiles, since they typically introduce large, narrow peaks and dips to the left and right of the center frequencies of the sliders used by the equalizer. Parametric equalizers are better at this, but the DSP that Dirac uses goes beyond EQ and addresses many if not most of the problems that relate to resonances and other driver/earpiece issues. The Jays Curves music player has a button to toggle the DSP on and off instantly, so you can compare the untreated sound to the sound with DSP. There's a certain roughness to the sound with the DSP off due to the t-Jays Four's basic signature which is uneven, but with the DSP on, not only does the signature become much more like a high quality headphone, but those rough areas get cleaned up as well. Any new distortions introduced with the DSP could affect long-term listening enjoyment, but my ears tell me that the DSP is essentially flawless. Note that the sonic correction I'm describing applies only to this version of the Jays Curves app, the current version t-Jays Four, and plugging the t-Jays Four directly into current Apple i-device headphone jacks. My tests with headphone amps demonstrated to me that altering any of these parameters could change the sound in unpredictable ways. The t-Jays Four looks like a typical IEM to me, but the earpieces are made with a ~40 degree angle rather than straight, and straight would have fit me better. There are a total of 5 different sized eartip pairs included. The basic cable is about 27 inches long, and the extension cable adds another 36 inches. The 3-button Apple controls and mic are located about 7 inches below the earpieces. In other reviews I've done I've included the following music examples with comments about how the headphones sound with each track. My suggestion is instead of reading each one as an absolute unto itself, you could compare my notes here to other reviews and see how the t-Jays Four compares with each individual track.