Apple's Lightning Headphone Adapter: Analog or Digital?
Back in June 2014 I reported on a little confusion that never seemed to be cleared up. The question is, "Can the Lightning port transport analog audio?" Most sources say no. But is that true?
Now that the new iPhone7 headphone adapter is out in the wild, tear-downs are starting...I'm sure we'll be seeing more soon. The first one pointed to in a 9TO5MAC article claims this Vietnamese adapter teardown shows the adapter has a DAC chip. Okay so far.
Then this German article (translated link) claims the adapter isn't as good as the headphone jack on the iPhone6 pointing to a loss of dynamic range. This Redit poster thinks it's all a bit silly. However, the article includes this (Google translated) tid-bit.
In the measurements, it was irrelevant whether the adapter to the iPhone 7, 7 Plus or iPhone 6S was attached: The results agree to the decimal. Strikingly, however, was that the adapter on iPad delivers significantly better result list than the iPhone. This may indicate that in the adapter no separate D / A converter is seated, but the audio signal is already transmitted in analog form via the Lightning jack. Since the Lightning chips with their remote site in iPhone / iPad can each negotiate in the cable, which is transmitted, that would be quite possible. As long as Apple is silent on the subject, can only bring further tests certainty here.
The article published this table of measurements (here translated):
What's interesting to me here is that the maximum output of the adapter changes when going from the iPhone7 to the iPad Air. If it is digital, shouldn't full scale be that same on both. Also note, when going from the iPhone6 jack to the adapter, and the iPad Air jack to the Adapter, the gain change remains the same at just under unity. Calculations were 0.88dB and 0.9dB...the difference can easily be chalked up to rounding errors in the published data.
Also, the output impedance changes slightly from 0.37 Ohms on the iPhones to 0.56 Ohms on the iPad, which it shouldn't do if it's all digital. If there is an analog out from the iOS device and a power amp in the adapter, there may be an analog feedback path, or possibly a slightly different output protection scheme on the two deviceswith an output impedance that low it's likely to need some protection circuits or sensing in the case of short circuiting when the plug is inserted or removed.
Well, there you have it, plenty of evidence for and against. My take is I'm glad it's got that low an output impedance, should be much better for people with mudlti-balanced armature IEMs.
DAC or Analog, what do you think?