Practically Agile

Using Agile in less-than-perfect situations since Y2K

IPhone-Bluetooth Audio Skipping Problem

For Father’s Day this year, my family gave me the gift of a stereo Bluetooth headset. I had been asking for one since the iPhone announced support for A2DP headsets. (Basically, simple stereo headphone support.) The one I got was the Plantronics Voyager 855. I can’t speak highly enough about it. There may be sets with better sound or build quality, but I haven’t had any problems with the set itself. And at just over $30 it is far cheaper than most. Listening to podcasts or music while mowing the lawn or whatever else is fantastic. The combination of in-ear buds that block out external noise and the wireless connection to the phone—I can’t believe I lived without it for so long.

However, the iPhone’s Bluetooth support is not the best. I have an 8GB 3G, and had a lot of trouble with the audio cutting out. Worse, the same was true when I was on a call. I could usually hear just fine, but folks on the other end would tell me that my voice was cutting out. I was starting to blame the headset and was preparing to buy a more expensive model.

Fortunately, I noticed two important things. First, the podcast/music audio cutting out tended to only happen when the screen locked. This was true whether or not I pressed the lock or let the phone auto-lock. Second, I noticed that Apple’s iPhone OS 3.1 update mentioned attempting to fix problems with Bluetooth and wireless (Wi-Fi). In their case, they were trying to improve Wi-Fi performance.

Because of this, I decided to experiment a bit. I disabled the Auto-Lock feature and disabled Wi-Fi. Suddenly, I had no more skipping and cut-out problems. People said calls did not cut out either. I tested this way for about a day. I was able to get the audio to cut out by launching a CPU-intensive app, but only during the launch. Once the app was running, the audio came back with no more problems.

After that, I re-enabled the auto-lock. I locked and unlocked the phone. Still no cut-out problems. I then turned Wi-Fi back on. No cut-out problems. Then I locked the phone. Bingo! Audio started cutting out again. I disabled auto-lock, but the problem was still there when I locked the phone. Finally, I disabled Wi-Fi and turned auto-lock back on. No more skipping or cut-out problems.

It turns out that the iPhone is built such that Wi-Fi and Bluetooth share an antenna (presumably to share space). This causes problems when both are on. Apple seems to have found a way to manage this most of the time and even released updates to improve Wi-Fi performance. However, as has been true of iPhone Bluetooth support all along, they seem to have neglected to do the same for Bluetooth. Specifically, something seems to happen to the Bluetooth power (and possibly the Wi-Fi power) when the phone is locked. The combination of signal degredation from both being on and the phone being locked causes the problem.

The moral of the story? If you want to use a Bluetooth headset, disable Wi-Fi. If you want to use Wi-Fi, disable Bluetooth. That will get you the best performance. Now back to enjoying my wireless music while refactoring.

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. 02 Oct 09 | Gadgets | Comments (5)