iPhone Dock and Headset IO Frequency Response

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

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 (with Tunewear Stereo Sound Recorder for iPod)

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.

15 comments

  • Alex W

    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?

    • ben

      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.

  • Paul B

    How good is the internal microphone for measuring vibrations?

  • randomdude

    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.

    • ben

      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.

  • Benjamin

    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

    • ben

      Apply for membership in the Made for iPod program to get access to the relevant documentation.

      • gmanni

        how do we apply for getting the documentation?
        I’m trying the same thing (trying to get audio input from dock on iphone 3gs)
        I know we can mute the mic in several ways but I’m not sure how to get the input from pin 5 and 6 to work.
        thank you in advance for your reply
        G.Manni

  • Einar Ristroph

    iPad 1? iPhone 4? Is there any frequency response data available on these?

  • Chris

    Hi, I was hoping to connect my bat detector to my iPhone4 and use this app to view the frequency of the sound. I am wondering if this app can detect and display ultra-sonic frequencies up to and over 100khz??

    • ben

      Chris,

      Our apps operate with a bandwidth of around 20 kHz. The iPhone audio hardware is not capable of supporting a bandwidth as high as 100 kHz.

      Ben

  • Leonardo Martinez

    Hello,

    Is it possible to disable the mic bias voltage in order to consume less energy?
    We will like to detect if an original headphone is used and we would like to use the mic input as a reference.
    If we could disable the mic bias, for example 1 second after insertion, power will be saved…

  • Chris G

    A quick look on ebay for iPhone original, or iPhone 2G headset with microphone results in a list for headset/microphones compatible with all models so isn’t working. What is the part number for the original iPhone headset?

  • Eric Delente

    I’m looking for recommended set up for the sigscopepro app — Are there any more recent updates available to this info? These are really helpful, but it seems that everything here is from a few years years ago. Thanks.

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