I use professional video equipment to shoot educational video for attorneys. I recently bought an iPhone 4S and intended to use it for quick video interviews and on-the-run educational video.

The Fostex AR-4i is an iPhone audio microphone adapter. It’s a piece of audio equipment that converts the built-in microphone on the iPhone into a true audio capture device to allow improved audio for your video.

Overall review: RECOMMENDED.

See the Fostex in action after the break.

If you shoot video using your built in microphone, you will get acceptable audio. Not great audio, just acceptable. The problem using your built in microphone is that you will also pick up all ambient sound. That’s why you never want to use your built-in mic when shooting video.

The Fostex AR-4i iPhone audio adapter solves that problem by converting your iPhone into a true video camera. Instead of relying on the built-in mic, the adapter, which is powered by two AAA batteries (included) allows you to use two mini omni-directional microphones that provide stereo sound.

The closer you are to the camera, the better quality and strength of your audio. The inherent problem with standing too close to the camera is that you begin to get a fish-eye effect with the micro lens on the iPhone. That’s the problem with using micro-optics.

Using these two microphone buds provides improved audio over the built-in microphone. Yet there’s an even better audio solution to get crystal clear audio using this really cool device.

The adapter has three microphone inputs. It only allows you to use two out of the three during video shooting. The adapter allows you to ergonomically hold the phone in a comfortable way and stabilizes the shoot by adding weight to the camera and adapter.
The adapter can be used in horizontal mode or vertical mode.

The best way to use this audio adapter is with a wireless microphone. Plug in the receiver into the microphone output and you will get ideal, crystal-clear audio.

Attach the adapter to a tripod and you’ve got a stable video platform where you can attach two wireless microphones for sit-down interviews.

One drawback to using this audio adapter is that every time I use it, I have to remove my iPhone case. Since I use a holster for my iPhone, it’s like removing a vise grip and very challenging.

Dismantling the device takes seconds.

Two other drawbacks:

  1. You cannot play the video back and listen to the audio while the iPhone is in the adapter cradle. No big deal. Just slide the phone out of the cradle and press play to watch your masterpiece.
  2. Prior to buying this audio device there were reviews online about audio playback issues using the iPhone 4S. In fact, the manufacturer specifically intended this device to be used for the iPhone 4. There is nothing on the manufacturer’s website about it being compatible with the iPhone 4S.

According to a few reviews, the playback issue on the 4S involved significant audio problems that made the video unusable. However, I watched a YouTube video review about this adapter and the reviewer used a 4S without a problem.

During my preliminary tests with my 4S I did not encounter any audio problems. It wasn’t until my 7th video test that I did hear a problem with the audio. I deleted it and started over. I heard the problem again on the 10th video test, but have not heard it since.

The manufacturer has a note on their website stating simply “We are aware of the audio problem associated with using our device with the 4S and are working on solving this problem.”

If you are looking for a different and unique way to create clean and crystal clear audio for your iPhone, you will appreciate the Fostex AR-4i.


  1. Syd says:

    Nice audio quality. No background noise for sure. Never thought we could use iphone for video recording client testimonials. Thanks

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