People often ask about the frequency response of iPhone and iPod touch audio inputs. To shed some light on the issue, I made some frequency response measurements of the iPhone, iPhone 3G, iPhone 3GS, and iPod touch 2G with Electroacoustics Toolbox and an Edirol FA-101 audio interface. These measurements are broken into two groups, one for headset input and one for dock connector input.
Since measurements were made by routing audio through each iPhone OS device (by way of the Audio Play Through function built-in to SignalScope/Pro), all measurements include the frequency response of the headphone output in addition to the response of the selected input. The frequency response of the Edirol FA-101 was removed from the measurement, using a not-yet-released version of the Dual FFT analyzer in the Toolbox.
The original iPhone wins, hands down, for the flattest frequency response of the headset input. It’s too bad that the iPhone 3GS drops the low end more severely than any other iPhone OS device.
Dock Connector Input (Line In)
I used a Tunewear Stereo Sound Recorder for iPod for these measurements. It has one of the flattest frequency responses I have seen in a dock connector device (more on that will be published soon).
There is some ripple evident in the line input frequency response (it’s not yet clear whether the ripple exists on the input, the output, or both), but other than that, the frequency response is quite flat. The low frequency 3 dB cutoff appears to be at around 7 Hz and things stay pretty flat beyond 20 kHz.