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I am wondering what maximum sample rate and bit depth is available through the USB connection to both the iPhone 6 and 7 (And any other models would be interesting).

I am a registered iOS developer so links to Apple confidential stuff (Or however is works) is OK but still not preferred.

Kind of related is this other question I just asked.

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3 Answers 3

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TL;DR: It appears the iPhone 6 supports 24-bit audio and 48 kHz playback.

So I found a way to empirically test playback.

This first screenshot shows a recording of playback over iPhone USB into Quicktime. You can see from the spectrogram that there is data in the 22-24k range, which means that playback is at least 48 kHz.

enter image description here

This next screenshot shows playback over USB straight into audacity. Basically, I played -95 dB and -97 dB tones at both 16- and 24-bit audio. -97dB is below the minimum volume of 16-bit audio. While all the other tones made a sound, the 16-bit, -97 dB chunk of the recording shows no sound, while 24-bit -97dB does play a sound.

enter image description here

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There appear to be vendors who sell USB audio ADCs and DACs that claim to be iOS compatible (via the Lightning Camera connection kit) and also claim sample rates of 96k and 192k.

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  • Yes I've noticed that. Another clue in favor of the iPhone being capable of high quality.
    – progressiveCavemen
    Commented Mar 21, 2017 at 14:02
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There appears to be no theoretical limit to the bit depth and sample rate an iPhone 7 can produce. The stock Apple apps and the built-in DAC used for the speakers and their headphones only support 16-bit at 48 kHz. That being said, devices plugged into USB/lightning port use their own DACs and iOS provides an interface in which an app (or your own code) can access the source file directly before conversion.

I can't link you directly to Apple developer resources for specific methods/classes, as I no longer have a developer account but this article seems to have a lot of the basic info, even though it's presented as more of a rant than anything else:

http://www.recode.net/2016/9/14/12904906/apple-iphone-7-audio-sound-quality-opportunity-airpods

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  • "Though few know it, Apple’s proprietary Lightning connector supports the ability to transmit uncompressed and even high-resolution audio in digital format to external devices." This seems to be the relevant section, but it really needs more information to be useful. Basically, [Citation needed]
    – progressiveCavemen
    Commented Mar 20, 2017 at 16:11
  • The built-in ADCs and DACs on the iPhone 6s and 7 use a native sample rate of 48000, not 44100.
    – hotpaw2
    Commented Mar 20, 2017 at 22:43
  • @popctrl I agree. It's hard to find much relevant info out there
    – rigormortiz
    Commented Mar 21, 2017 at 1:53
  • @hotpaw2 thanks for the clarification. I've read conflicting data, but 48k makes sense, given Apple publishing tools dither to 48k by default for AAC output. I've edited my answer to reflect that.
    – rigormortiz
    Commented Mar 21, 2017 at 1:53

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