@romanrex which is the best DAP you've measured so far?
This is not a simple question. When comparing players, it is necessary to take into account equal conditions. All players have different output power.
For example, the player "X" shows good results, but it's quiet. Another player "Y" shows in a similar quiet mode a similar good result. But the "Y" player can work and "loud" and in this mode its characteristics are bad. If the player X can be called good, then the player "Y" is good only in direct comparison with "X". At what level should we compare the players? This is not the only true answer.
Another example is the difference in quality when adjusting the volume with an analogue controller and digital level control in the DAC.
For example, in the player "N" the controller is analog. From the output of the DAC to a level of 0 dBFS, distortions increase. This distortion of the analog circuit from the DAC. When the volume is reduced by an analogue controller, these distortions remain. If the player "N" would be a digital controller, then the decrease in the amplitude to reduce these distortions.
But let's take the player "M" with a digital controller. When the volume decreases, the distortion from the analog DAC circuit is eliminated. Assume that we have enough volume for the selected headphones. There may be another problem.When the volume decreases, specific DAC distortions appear. The reason can be as its modulators, digital filter or power supply.
For example Benjie X1
When the volume level is reduced, the distortion does not decrease. At small amplitudes (-40dBFS ~ -60 dBFS), distortions to the main signal are high.
Accordingly, in direct comparison at a low volume, the player "N" will have distortions from the analog circuit, and in the player "M" from the DAC itself. The distortion of the headphone amplifier in this example was not taken into account.
If to allocate good results without direct comparisons. Good results from line-out and from headphone amplifier with full volume.
Cayin N6
Colorful Colorfly C4 Pro
FiiO X5-III
FiiO X7 II
Pioneer XDP-300R
Oriolus DP100
iBasso DX150
iBasso DX200
Hidizs AP100
Shanling M2s
Shanling M3s
xDuoo X20
Each of the players is not perfect, but it has good characteristics. Players that were not tested with a multitone signal were not included in the list. The list did not hit the players with a loud amplifier, but high-quality work only at a quiet volume. Maybe I missed some player.