This and That:
Quite inexpensive and promises many features. Nonetheless it's ultimately (clearly!) inferior to my SanDisk Sansa Clip Zip, Clip Plus and several AGPTek digital audio players in several areas, and all of them cost less than the Hidizs AP60.
Anyway, it's rather nice that earbuds are already included (even with a pouch and foam attachments).
Screen protector already installed (a spare one is included, too).
Nice metallic red colour, however the plastic that's used isn't of the high quality kind. Small and nice form factor though.
The illuminated capacitive touch button navigation pad sucks big time. Physical buttons would have been so much better, as navigation is super cumbersome and lacks precision with those small buttons that are indistinguishable (no tactile differentiation/borders/whatsoever on the surface) if not carefully looked at.
UI okay-ish. Folder browser is fortunately included.
Playback screen doesn't show the entire album cover but scales it to cover the entire screen.
80 volume steps (used to be 120 in very early firmware releases, but they've reduced the step size (it's coarser now) and now it's only 80 steps). Listening quietly is possible, though.
FLAC file gapless playback works perfectly.
USB DAC output works since 1.01beta.
USB DAC input (Windows with additional drivers) works since 0.05beta. Nice: the screen displays the volume settings and bit/sample rate.
Sound:
Frequency Response (simple Loads):
Consistent bass roll-off that's not influenced by the load impedance; otherwise mostly flat.
That's quite poor for a modern day device, even for a quite inexpensive one.
Frequency Response (complex Load (Ultimate Ears Triple.Fi 10)):
The calculated output impedance around 1.5 Ohms, which is okay but higher than what Hidizs state, which (along with the bass roll-off) leads to the question whether Hidizs have actually performed any measurements at all or just stated the chips' specs without implementing them properly.
Hiss Performance:
Quite weak headphone output, however quite strong hiss with very sensitive in-ears (such as my Shure SE846 or Ostry KC06A). Still some hiss with less sensitive in-ears (such as my Sennheiser IE 800).
Subjective Sound Perception:
As the other measurements aren't great either and beat by smartphones with decent audio implementation, however not utter garbage, it's not too surprising that due to the hiss and noise floor modulation, the sound gains a very slight warm tilt. In addition, high instruments appear to lack a little definition, subjectively.
It's all not night-and-day and pretty subtle, and perhaps subtle enough during carefree recreational listening, however noticeable while performing volume-matched (but sighted, so not a blind test) comparisons. With the right music and headphones that extend low and are very familiar, the roll-off towards the sub-bass is noticeable as well.
Bluetooth:
Bluetooth streaming (into headphones and other devices that are receivers) works and sounds well thanks to the aptX license and support (of course provided the receiving devices support aptX as well, else the stream will be in lower quality), so Bluetooth streaming is really the only area where the AP60 does a good job.
I wouldn't use it as a Bluetooth receiver though, as its output doesn't measure too well (bass roll off and other values).
Conclusion:
The Hidizs AP60 sucks.
Its features (bidirectional Bluetooth; bidirectional USB DAC) seem attractive at first but the player's measured audio performance is nothing but quite poor for modern day standards and beat by many other products in the same price range and even below. Especially the permanent bass roll-off is a no-go. Navigation/operation sucks big time due to the poor choice of capacitive buttons instead of physical ones.
Only recommendable as an inexpensive device for aptX Bluetooth transmission, but I'd recommend other devices with superior navigation for this purpose, although it may be difficult to find something with aptX Bluetooth streaming for that price (nonetheless I was able to get my BlackBerry Classic brand new (new old stock) in a sale for less than what the AP60 costs).