perfecious
100+ Head-Fier
i don't own an axon 7, but these are my guesses. i might be wrong, if someone knows more info, please correct me.
none of the DACs of the axon 7 (AK4961 -standard mode- and AK4490 -hifi mode-) are colored. they provide flat frequency response, as you showed in your graph (white line):
it might use different amplification (as well as different DAC) for each mode, to adapt amplification gain to the ear/headphones. decreasing gain by using resistors would be absurd.
but the amplification should be flat as well, except if they implemented a weird amplification, which i doubt, and if no DSP, EQ, boosts, or other alterations are applied.
let me insist on it: the coloration you get is not due to DAC nor amplification, but due to high output impedance probably.
you can check it by measuring with rmaa, like you did, ensuring DSPs are disabled, using flat impedance headphones or iems (only dynamic drivers) of around 20ohms, and then using your multi-BA DM6 (no flat impedance).
you'll probably get much more alteration with the latter.
and then, you'd earn nothing by using a regular impedance adapter (tonal alteration would be even worse).
GSM arena actually measured it incorrectly (which was discussed many times), that's why they actually have hid the review, but because I'm me, here's the super-secret link. You can compare it wit the results that Juan Bagnell form pocketnow did (and I trust him completely, because he loves audio and knows what he's doing), using the "Focusrite Scarlett 6i6 (2nd Gen)" interface (that I wanna get for running my tests). He even does IEM reviews now as well.
Anyway, GSM arena used the stock player in SuperHifi mode, which is the only combo that uses that particular "coloration" to it's max, or sound enhancement, that is called "Velvet Sound", which is AKM's proprietary enhancement (same like Sony's DSEE HX), and it's exactly what it looks like on the graph. It's an AMP based regime (filter) designed for the 4490EQ DAC. Some people (with cold/analytical headphones IEMs) love it (like me with the T2's, which is understandable from looking at the graph, it's like an bass-boost EQ), others (with transparent and already warm IEMs like the DM6) hate it (also me in that case). I think HBB mentioned that same thing with the iBasso DX200 I believe, with it's original amp module. It's not a problem with the amp (the "Velvet" sound), it's actually a feature
, that changes the sound to "improve it" on crappy gear, but makes good gear sound terrible. And as I've said, the higher internal impedance WILL AMPLIFY extremely that "completely intentional" coloration of the DAC/AMP combo in SuperHiFi mode. Something like this:
As you can see, if the output is completely flat (like the the mini, and it's not that flat as well, only the regular HiFi mode is flat/netrual), amplifying (because of high-gain) an straight line wouldn't change the signature. It will only increase amplification noise, whihc is exactly what is happening with the mini as well. (but at least it doesn't pick up coil whine and wifi as bad as the axon 7, which apparently has some sort of EMI shielding problem in it's audio section as well/ BTW, I've checked a review by Nathan P. on amazon for the DX200 DAP, and strangely, it had the same problem with wi-fi, making the DAP completely unusable with sensitive IEMs and streaming with WiFi, but that's just another piece of the same pie...)
The "velvet sound" is intended to be used as something to "enhance" crappy headphones, and recreate "missing information" from compressed audio. Clearly, it doesn't work if the IEM is completely transparent (like the DM6), and already warm/good sounding, or with good audio files. You are basically adding layers on top of layers of coloration, which get even more extreme by the "higher gain" regime (or higher internal impedance caused by working in 32ohms when the IEM is 20). And you all know what impresses people most - loud V-shaped noises
LOLz (it's a gimmick basically, that I will admit works in some cases, in others is like slap in the face).So, GSM arena actually measured exactly that SuperHiFi coloration, which is basically like an EXTREME EQ. I mean I can recreate that using parametric EQ on my UAPP player in normal HiFi mode, and it will sound exactly like as if it's in SuperHifi mode.
The Mini axon doesn't have that coloration, and it's very neutral/analytical, so even with the internal impedance problem (which it also has, because it sounds noisy as ***), there is nowhere near the "shift" in tonality as the colored big brother. Which is why I've been recommending it as a neutral/analytical device. I can hear that as a quality though (as in fidelity/smoothness and detail), the AK4490EQ on the big axon 7 beats it. I've listened to both back and forth yesterday on the DM6 (normal HiFi mode), and the best way to describe it, is the mini is "fuzzy", while the Axon 7 is very smooth (probably due to some anti-aliasing+rollof filter applied, in combination with the velvet sound, but yeah, you know the rest).
Dammit, this got too long again... Really sorry.
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