Research
Unfortunately, Apple does not release information or specs of their devices on their website. There are third parties websites with what seem like credible information, but even then the Iphone 6s is an outdated model that can be perceived as obsolete face to the new Iphone models. What I can say, is that the Iphone 6s has 3 microphones: one on the back of the phone by the camera lens, one on the front of the phone by the camera lens, as well as two on the bottom of the phone (on the left). The phone, according to Apple, should have somewhat of a flat frequency response from 10Hz to 10kHz, for recording speech. I was unable to find any other pertinent information.
Record
The app used to record the sine sweep was: Auphonic Recorder
The app allows the user to:
- Turn the gain off or on
- Choose which microphone utilize
- It allows a choice of format (AAC audio or PCM/ WAV audio)
- Choice of precision of recording (16 or 24 bits)
- Allows a sample rate of up to 48kHz
For this Recording the specific setting chosen were:
- Gain: off
- Format: wav
- Sample rate: 48 kHz
The program I used to analyze the sweep was Oceanaudio. I analyzed a 15 second recording on FFT with a linear scale.
At first, I used my BOSE speaker to record the sine sweep with my phone about a foot from the microphone (The volume of the speaker was actually pretty loud). After using Oceanaudio to analyze the recording I got this:
[could not manage to uplaod graph]
According to the FFT analysis, we can see that the frequency response of built-in Iphone 6s microphone (bottom one) seems to be not very flat at all after passing the 1kHz mark. Before then, the frequency response is quite flat. However, after passing the 10k Hz range there are significant dips in the frequencies (for example at 6kHz, 8.5 kHz or 11 kHz, etc…). I wanted to try recording again but at a closer distance of the phone to the source to see if the dips were caused by outside faint sounds.
I did another recording, this time putting my phone between by Sennheiser headphones so that the Iphone 6s microphone could be as close as possible to the source. This time the FFT analysis provided this:
[could not manage to uplaod graph]
Here we see by actually moving the phone closer the frequency response of the sweep is flatter from 100 Hz to 9kHz but dips down significantly after 10kHz.
Report
The Iphone 6s is an older Iphone model which does not reproduce sound as well as the newer models and as other phones, when recording at a distance it is inaccurate. It does however reproduce sound very well when the sound is very close and in the 10 Hz to 10 kHz range. This shows how the Iphone 6s is not a phone meant to record music or singing, it is strictly a phone created to talk and used to call and clearly hear people on phone calls (speech is very much in the 10 Hz to10kHz rang. This all makes sense for an older model Iphone giving up microphone recording capabilities at various frequencies in order to capitalize on the frequencies used to communicate through phone calls.
You make an interesting point about how the phone’s primary purpose is for talking (vs. singing), and how the range of the human voice is contained in the range in which you found that the sound was reproduced well!
I also like how you linked the frequency response range to the most basic purpose of the device — processing and relaying the human voice. I also found it extremely hard to find official specs on apple products, so you’re not alone.