The iPhone 11, Mic’d Up

Unpacking the iPhone 11 and the rationale behind 48kHz

Per Apple’s design specs and initial observations, the standard iPhone 11 has three microphones (all stereo).

Apple fails to officially report the product’s microphone’s maximum sample rates and bit depths, leading to conflicting information across discussion boards and third-party websites – however, per the most common figure and having figured out in practice, it appears that the iPhone 11 microphones are equipped with both mono and stereo input capabilities, at a maximum sampling rate of 48000Hz and bit depth of 32, progressing from the former 44.1kHz industry standard generally employed to export audio to CDs. It was simultaneously quite interesting to find that 48kHz sampling rates are becoming increasingly desirable for their compatibility with video standards.

Regaining control: Finding the right app

Finding an recording app that ensures uncompressed audio and the absence of built-in gain control was an intriguing process. 48kHz audio sampling is becoming increasingly common, allowing most standard recording apps to tick this box; although, interestingly, Apple’s own GarageBand records at 44.1 kHz.

I had a crack at a few audio recording apps: Dolby On enabled lossless exports and 48kHz/16-bit recording but seemed to suggest it had AGC in place (see below), neither Røde Reporter nor Rec seemed to suggest they could disable standard iOS gain control and Hooke Audio did not seem to support anything other than AAC/MP3 exports. As such, I opted for software developer Dayana Networks’ Voice Recorder Pro as my recording software, as this app was capable of executing each of the recording specifications of this experiment.

Putting it all into practice

I used Audacity to generate the sweep at a constant amplitude of 0.5. Using my laptop’s dual speakers, I placed my phone next to the left speaker, right speaker, at the center of the laptop, and 6ft away from the laptop (social distancing and its impact on spectral flatness?), and recorded each individual sweep using Voice Recorder Pro. After noticing negligible differences in spectral flatness between the location of the phone in regard to particular laptop speaker (i.e R/L, center), I repeated the short distance experiment outside of the suite, to observe the impact of background noise on the iPhone’s recording ability.

Here were the results:

It can be seen that the iPhone 11’s mic is able to pick up the majority of frequencies at a reasonable level; the perceived lack of flatness in parts of the FFT analysis can partially be attributed to background noise, and we can generally conclude that the spectral flatness and FFT results of the phone recording is dependent on a) the loudness/distortion of the output, b) the distance from the output (shown by our “socially distanced” recording 6ft away from the laptop and c) the room size (taking a recording in the courtyard demonstrated a noticeably quieter, “messier” and less flat recording, despite distance being similar to that of the recordings taken adjacent to speakers). Qualitatively, the lack of an oscillation in peaks demonstrates a solid spectral flatness to the iPhone 11, making its three stereo microphones of a clearly high quality and justifying android slander universally.

Sites consulted:

https://www.provideocoalition.com/48-khz-how-to-set-it-in-android-ios-macos-and-windows/#:~:text=Setting%2048%20kHz%20audio%20sampling%20in%20iOS,Airlinc%20(reviewed%20here)

https://www.provideocoalition.com/all-audio-production-distribution-should-go-48-khz-learn-why/

https://www.gizmochina.com/product/apple-iphone-11/

https://forum.juce.com/t/disable-agc-and-highpass-filter-on-ios/12812

https://www.apple.com/iphone-11/specs/

https://www.howtoisolve.com/where-is-microphone-in-iphone-11-pro-iphone-11-pro-max-and-iphone-11-exact-locations/