Sadly there is no English version, but here's the German article with the important bits translated:
http://www.heise.de/ct/artikel/iPho...apter-liefert-schlechteren-Sound-3325932.html
Curiously, while all iPhones (including the 7) sound the same, iPads get a better result with the same adapter. The magazine speculates that the DAC therefore isn't inside the adapter, but the device and the analog signal is transported via Lightning. Which contradicts what I thought I read somewhere, namely that Lightning can't do analog signals. Also, it's a bit weird that an iPhone 6S can do better audio via the 3.5 mm jack than the Lightning adapter if the DA conversion happens on the iPhone.
And of course, this is only the case if you want to use existing "analog" headphones, not Lightning or Bluetooth ones.
http://www.heise.de/ct/artikel/iPho...apter-liefert-schlechteren-Sound-3325932.html
The results are clear: with an iPhone 6S, the dynamic range worsens by 4.5 dB(A) for 24-bit music files. For the iPad Air, it worsens by 3.8 dB(A). The signal also gets worse for 16-bit music files, even if they aren't that drastic: the dynamic range worsens by 1.8 dB(A) and 3.1 dB(A) for the iPhone and iPad, respectively.
The differences should be discernable with headphones costing 100 upwards, especially with uncompressed music files at 24 bits. For lossy compressed files (MP3, AAC), most users probably won't hear a big difference.
Curiously, while all iPhones (including the 7) sound the same, iPads get a better result with the same adapter. The magazine speculates that the DAC therefore isn't inside the adapter, but the device and the analog signal is transported via Lightning. Which contradicts what I thought I read somewhere, namely that Lightning can't do analog signals. Also, it's a bit weird that an iPhone 6S can do better audio via the 3.5 mm jack than the Lightning adapter if the DA conversion happens on the iPhone.
And of course, this is only the case if you want to use existing "analog" headphones, not Lightning or Bluetooth ones.