I immediately updated the firmware. I will report the result.
The test was performed by randomly switching the files from PCM44.1kHz to PCM768kHz and DSD2.8 to DSD22.5.
1. The previously reported problem of pop noise has been improved.
2. We have also improved the strange display on the display when switching songs. However, there are still times when the Err display momentarily appears.
3. In the middle of the test, when I switched between songs, the loud noise was played only once.
4. Playback on DSD 2.8 is not improved. This problem seems to require hardware improvement as Topping says.
I'm sorry for my alway poor English.
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5. When DSD is played after the factory reset of E30, the phenomenon that a loud noise is heard for a moment when the playback starts is not improved.