USB Audio Devices that work with iPad

The discussion of issues surrounding the iPad’s USB audio support in the previous post certainly begs the question, “Which devices work properly with the iPad?” In the table below, I list the devices I have tested with the iPad, along with some observations.

iPad USB Audio Device Compatibility

Please keep in mind that the iPad Camera Connection Kit is required to connect USB audio devices to the iPad (see the previous post).

Input Output Bus Power Notes
ART USB Dual Pre Data Loss (1) Works (2) Yes The USB Dual Pre runs on bus power, even with phantom power on. It can also run on a 9V battery.
Behringer UFO202 Data Loss (1) Works (2) Yes
Blue Icicle No N/A N/A The iPad completely rejects the Icicle with the message: “The attached USB devices is not supported.”
Griffin iMic Works Works Yes I tested an older model, but others have confirmed that the newer model also works.
MXL Mic Mate Classic Data Loss (1) N/A Yes (3) Phantom power is always on. No output channels.
MXL Mic Mate Pro Data Loss (1) Works (2) No Phantom power is always on. A self-powered USB hub is required to use the Mic Mate Pro with the iPad.
Nady UIM-2X Works Works Yes (3) Unfortunately, the UIM-2X rolls off low frequencies, below 200 Hz, which makes it undesirable as a measurement device.
  1. Input data reaches the iPad, but it gets corrupted, apparently because of improper clock synchronization.
  2. Audio output works fine, as long as the iPad app does not also retrieve input data. For example, the ART USB Dual Pre works fine with SignalSuite, which only uses audio output. The same device produces audible glitches in its output when used with SignalScope Pro, which uses the device’s input and output channels.
  3. If the input device draws too much current, the iPad will refuse to work with it, even if the iPad had already been working with the device. For example, even though the Nady UIM-2X presents itself as a high power device (one that requires more than 100 mA of current from the USB bus), the iPad will work with it until you turn the UIM-2X’s phantom power on. At that point, the iPad will indicate that it draws too much power and switch audio back to the internal mic and speaker.

In summary, of the devices mentioned above, only the Griffin iMic and Nady UIM-2X work properly for both audio input and output with the iPad. Audio output generally works on output-capable devices, although some devices produce audible glitches when both input and output are used by an iPad app. Unfortunately, there still isn’t a simple, bus powered solution for connecting a phantom-powered measurement microphone to the iPad.

Feel free to share your iPad USB audio experience in the comments.

USB Audio on iPad

As I mentioned in a previous post, the iPad does not support audio line level input through its 30-pin dock connector. This would seem to be a major limitation of the iPad, as far as audio-band test and measurement is concerned, if it weren’t for the fact that the iPad can function as a USB host for USB audio input/output devices. Unfortunately, however, connecting a USB audio device is not as straightforward as it might seem. The goal, here, is to enumerate some of the current issues with USB audio on the iPad.

Add a USB port to your iPad with the Camera Connection Kit

USB audio support on the iPad — issues to be aware of:

  • USB devices currently must be connected to the iPad via the USB port of the iPad Camera Connection Kit. It’s the USB-dock adapter in the camera connection kit that switches the iPad into USB host mode.
  • The iPad can only provide bus power to low-power USB devices (those which draw 100 mA, or less, of current). Devices that require more power can still be used with the iPad, but they will either need to be self-powered (typically via a battery or AC adapter), or they will need to be connected via a powered USB hub.
  • The iPad supports full-speed, 16-bit, USB audio class compliant audio devices. High speed and 24-bit devices are not supported. Devices which to not conform to the USB audio class are also not supported. If a device supports both 24-bit and 16-bit operation, it should be switched to 16-bit mode before it is connected to the iPad.
  • Only sample rates up to 48 kHz are supported.
  • When a USB audio device is used for input, neither the iPad’s headphone jack nor its built-in speaker can be used for output. Both input and output are routed through the USB port, by the OS.
  • Asynchronous USB audio devices experience periodic data loss when used with the iPad. (Hopefully, Apple will move to properly support asynchronous USB audio devices, soon, since this essentially renders useless a significant number of otherwise capable devices. I’ll indicate which devices I have found that fall into this category in a future post.)

iPad Audio Input Options

It turns out that in some ways, getting audio signals into the iPad is similar to getting audio signals into the iPhone 3GS, and in some ways it’s not. Like the iPhone, the iPad includes a built-in microphone as well as support for a headset microphone through its headset jack. Unlike the iPhone, the iPad does not support audio line level input via the 30-pin dock connector, so you won’t be able to use existing iPod mic/line accessories with your iPad.

The iPad’s lack of audio line input support would appear to be a major limitation of the device, particularly for audio test and measurement apps. However, it turns out that the iPad can act as a USB host with support for 16-bit, 48 kHz USB Audio Class compliant devices. All you need to do is plug a compatible USB audio device into the USB port of the iPad Camera Connection Kit and you’re good to go. (I’ll spend more time explaining what “compatible” means in a future post.)

Frequency Response

So how does the frequency response of the built-in microphone and the headset input compare? I measured both and offer comparisons with the iPhone 3GS. It turns out that the two devices have very similar characteristics for their mic inputs.

The iPad's built-in microphone frequency response is nearly identical to that of the iPhone 3GS.

The iPad headset input seems to begin it's low-end rolloff above where the iPhone 3GS does, but again, their responses are similar.

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