iOS Audio Hardware: Stereo input via USB

If you’re looking for a way to acquire stereo input signals in apps like SignalScope Pro or IOScope, you’ll be pleased to know that you can connect a USB audio device to your iPhone, iPad, or iPod touch via Apple’s Lightning to USB Camera Adapter. Built-in USB audio support in iOS opens up a vast array of options for getting audio signals into, and out of, your iOS device. (USB audio support on iPhone and iPod touch requires iOS 7 or later.)

Compatibility

The trick is to find a device that conforms to the USB Audio Device Class specification, which essentially means that no special drivers are required when connecting the device to a host, like a Mac or an iPhone. Some device manufacturers clearly state that their product works with iOS and some do not. In general, if you find a USB audio device that does not require special drivers to work with Mac OS, then it will work with iOS as well.

Power

One thing to consider when selecting a USB audio device to connect to your iPhone or iPad is power. Some USB audio devices require an external power source, which means portability will be somewhat limited due to the need to have an A/C power outlet nearby. Other devices support USB bus power, which means they’ll draw their power from the host device (e.g. the iPhone). For portability, this would be the ideal situation since the iPhone and input device could be completely portable and operate for the life of the iPhone’s battery. However, only low-power devices can be directly powered by an iPhone or iPad, which means that a lot of otherwise compatible USB audio devices cannot be connected to iOS without some other source of power. For bus-powered USB devices that require more power, it is possible to maintain some portability with a USB battery power supply and an additional adapter cable.

A Few Examples (portable and inexpensive)

Stereo USB Audio Devices
Behringer UCA202
The UCA202 from Behringer offers very inexpensive and portable stereo input for iOS.

It features:

  • 16-bit/48 kHz sampling
  • 2 inputs and 2 outputs with RCA jacks
  • Headphone output with volume control (1/8″ jack)
  • Low power operation so it can be powered directly by an iPhone or iPad
  • S/PDIF optical digital output
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Behringer UFO202
The Behringer UFO202 is similar to the UCA202. Instead of a digital output, it offers the option to select between line-level and phono preamp input.
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ART USB Dual Pre
Another inexpensive option, which also adds mic preamps with switchable 48V phantom power, is the USB Dual Pre from ART.

It features:

  • 16-bit/48 kHz sampling
  • 2 inputs with XLR / 1/4″ combo jacks for mic preamp or line-level input
  • 2 outputs with 1/4″ jacks
  • Headphone output with volume control
  • Low power operation so it can be powered directly by an iPhone or iPad
  • Switchable 48V phantom power, powered from a 9V battery
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Adapters
Apple Lightning to USB Camera Adapter
This adapter is all that’s needed to connect a compatible USB audio device to an iPhone, iPad or iPod touch with a Lightning connector. As indicated above, if your USB device needs additional power, additional components will be needed. That will be discussed in a separate article.
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Apple iPad Camera Connection Kit
If you have an older iPhone or iPad with a 30-pin dock connector, you can connect a USB audio device with the USB adapter included in this kit. Remember that iOS 7 is required for USB audio on iPhone.
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