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.
Headset Input
Headset Input Frequency Response
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).
Dock Input Frequency Response (using Tunewear Stereo Sound Recorder for iPod)
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.
I’m a little confused as to the frequency response of audio data available for use WITHIN the iPhone.
So, if I get audio input using SignalScope through the headset on my 3GS, is the data that I’m seeing on screen already missing < 100Hz?
That’s basically correct. When you use SignalScope to analyze a signal coming in through the iPhone 3GS headset connector, the frequencies below 200 Hz have already been attenuated according the curve you see in the plot.
How good is the internal microphone for measuring vibrations?
Actually the lastest iphone wins, for the headset input, and the bass drop is probably intended and refined on each passing generation.
Your voice cannot go as low as 100Hz so the only thing you’re going to pick up there is unwanted noise. Flatter is not always better.
Of course, it depends on what you’re trying to accomplish. Since this post addresses the issue of using the iPhone for audio/acoustic test and measurement, flatter would be more desirable.
Hello guys, i want to use the Dock Line In at my iphone 3G. I have a 30-Pin Dock Connector with all pins are occupied. But when i connect the Pin 2, 5, 6, the internal Microphone don´t get Muted and the Input doesn´t come from the Pins 5,6. What can I do ?
Thanks
Benjamin
Apply for membership in the Made for iPod program to get access to the relevant documentation.