The audio sample rate determines how many audio samples per second are recorded. In this article the rate is measured in kHz (one kHz being 1000 Hz or 1000 samples). The standard audio sample rate for video is 48KHz.
An important factor about sample rates and iOS is that the input and output sample rate must match. This means that if you connect a set of bluetooth headphones as an output, then the input must match this output.
MAVIS follows the standard iOS "last in wins" rule, where the last device plugged into the device (as either an input or output) is the dominant device. For example, if the last device plugged into the iPhone was an external mic then MAVIS will automatically choose this microphone as the input to the recorder. Similarly, if the last thing you connected to the iPhone was a pair of bluetooth headphones then MAVIS will attempt to route the headphone monitoring output via bluetooth (with potential consequences to the sample rate of the input).
Lets look at some examples.
In this example we have an input which is sampling at 48KHz. We also have an output which is sampling at 48KHz. Because both the input and output are at 48KHz MAVIS will also default 48KHz for any recorded audio.
In this example we will start with the output - a pair of bluetooth headphones. iOS can support bluetooth headphones and the normal output sample rate for such a device is 44.1KHz. In this case the headphones are using a sample rate of 44.1KHz. Based on the requirement that the input match the output, the input device has dropped to 44.1KHz. You will notice that the input device is the same as in Example 1 and is therefore capable of sampling at 48KHz. However, because the input must match the output it has been limited to 44.1KHz. MAVIS has therefore defaulted to 44.1KHz to match both the input and output.
In this example we have an input device, the internal iPhone mic, and we have no output device. This just means we are not using any headphone monitoring and have therefore disconnected the headphones. Our input device is sampling at 48HKz and MAVIS therefore defaults to 48KHz to match.
In this example we have an input which is capable of sampling at a maximum of 44.1KHz. Based on this input sample rate both the output and MAVIS have matched the input and they have defaulted to 44.1KHz.
How to check the current sample rate within MAVIS?
1) Tap on the Audio icon at the top right of the screen (icon may differ slightly due to audio devices connected)
2) Tap on the Audio Settings icon within the audio flyout menu
3) Scroll down to the bottom to view an info statement about current sample rate