This is a review and detailed measurements of the iBasso DX120 portable Digital Audio Player (DAP). It is on kind loan from a member and costs USD $319 from Amazon including Prime shipping.This is a chunky device if you are used to portable players from likes of Apple or your mobile phone:The user interface is attractive and quite fast in browsing menu options. This was better than I expected as was the nice color scheme and graphics.I usually go to company website to learn more but had a heck of a time doing that with this product. The moment you select DX120 you get this graphics laden page that is a pain in the neck to navigate. You can't scroll through it and have to keep clicking on radio button on the right. Some web designer went crazy designing this page.I was very pleased to find that using the USB cable, I could treat this as a Windows DAC. This enabled me to run my full suite of measurements which I can't normally run when I have to play content manually in the player. Yes, I tested both modes of operation to make sure DAC mode is representative of DAP playback. See measurements later.There are three sets of "headphone jacks" at the bottom. First one is 3.5mm and is for line out. The second is also 3.5 mm but is for headphone. The last is 2.5 mm which is for "balanced" headphone output. I tested all three.As far as cabling, there is an oddest inclusion: a "burn-in cable!" Yes, it does what it says. You are supposed to plug it into the headphone jack and let the unit play for many hours to "form capacitors and such." It seems to have a small dummy load it and you are warned to not run the player at full volume into it.Let's get into measurements and see how she does.I started with USB DAC mode and line out. Here is our dashboard view:Output is a bit low at 1.8 volts (like to see 2 volts) but otherwise, performance seems pretty good for a portable device. By dialing the digital level by 1 dB I could get a SINAD of over 100 dB. Here is how it ranks as is:It barely misses our tier 2 performance of all DACs tested.Dashboard view with headphone out generated similar results (high gain/max volume):Here, we do get to 101 dB which would put it in tier 2. So far so good.Dynamic range is very good too:Intermodulation test is pretty decent too:Jitter is unusually clean:Surely linearity would be bad, no?No, that is excellent too!How about multi-tone?Nothing bad jumps out.I usually skip frequency response tests because digital products do so well here. In this case, I decided to run it because of a handful of "sound modes" in DX120:What the heck happened here? Not only do the different modes do nothing, but there is a roll off that starts at just 1 kHz! I measured and remeasured with the same results. To make sure my instrumentation is OK, I ran the same test on Topping D10 (in dashed red) and the output is as one expects: essentially ruler flat response. I am at a loss as to what is happening here. And if correct, how people have not noticed such a sharp roll off.FYI to make sure firmware bug was not in play, I updated the unit to the latest available (2.4.59) release just this month. Yes, I checked the EQ and shut it off but it made no difference. I will do some more testing at different sample rates and see if that makes a difference.Next unusual result was THD+N versus frequency:This is when I started to go crazy. I just saw the identical sharp peak starting at 5 kHz when I measured the Marantz AC8805 processor . Let's dig in just the same to see if the issue is lack of proper filtering in the output of the DAC:It is. The default which is the slow roll off is horrendous (magenta). But even fast roll off takes its time. So is my instrumentation broken? Let's run the identical test on Topping D10 again (red):The D10 is performing as we expect so instrumentation is fine. But how could two radically different products have the same problem? Could it be that they both use the same DAC? They do! Both the Marantz AV8805 and iBasso DX120 use the AKM AK4459 dac chip! Fortunately unlike ESS, AKM publishes their spec so we can look up the performance metric for the different filters. Here it is for Sharp roll off:We are supposed to have 100 dB of attenuation once we get to 24.1 kHz. I put the blue cursor there and we are only seeing 8 dB of reduction!Can both of these companies be programming the AKM DAC incorrectly? I am at a loss as to what is going on here. Happy to take suggestions for additional tests to figure out what is going on. Hopefully we can get iBasso to investigate this (no hope of getting through to anyone at Marantz).Let's keep going and see how well the headphone amp works starting with performance at 300 ohm:We have decent level of noise although that may be due to roll off of the high frequencies. Power though is very low at just 11 milliwatts. For perfection I like to see 100 milliwatts so we are quite far from that.At 33 ohm, the situation does not improve much:Testing balanced output though gives us hope:As expected, we get four times the power with lower noise and distortion to boot.Volume control is digital so channel balance is perfect:Output impedance is a very good 1 ohm:I still have not had time to fashion a balanced headphone cable for my Sennheiser HD-650. So had to use the normal 3.5 mm jack. As expected, there is just no "oomph" there. I would be listening at near max volume for a lot of music in my library.The situation improved some with the Hifiman HE-400i. Depending on music, there was decent volume and bass. In some cases though, I was back to full volume and wishing there was more.If you have the option of using balanced connection, you should be in much better shape. Or alternatively use more sensitive IEMs or headphones.The iBasso DX120 starts the show well with good distortion and jitter metrics. Then we hit a major snag with frequency response that has very large high frequency roll off. That then got compounded with digital filter settings which seem quite wrong. If they can fix these two bugs, I would be able to put the DX120 on my recommended list. As it is, it has missed the basics.------------As always, questions, comments, recommendations, etc. are welcome.Just collected all of my pennies to afford the nice Carne Asada we had for dinner tonight at the local restaurant. Before my pocket develops a hole, would appreciate some replenishment of those funds using: https://www.patreon.com/audiosciencereview ), or https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).