Voice call audio clipping and dropouts on iPhone 5: hardware failure, bug, or network issue?

Modern voice quality is highly variable at the best of times, and I don't do all that many business calls on my mobile, so it took me a while to realize there was something very wrong with the voice quality on my AT&T iPhone 5 phone calls over the MSP LTE/3G network.

This post in a 27 page Apple Discussion thread matches my experience (emphases mine), except that many reports are from Germany as well as AT&T.  Some have problems only at particular locations. The thread describes many different issues, some of which seem to be Verizon specific or defective headphones and the like -- but this is the one I get.

https://discussions.apple.com/message/20440496#20440496 (sk1sk1)

... when on a phone call on iPhone 5, the sound from the distant party cuts in and out, drops entire words and phrases, the beginning and end of utterances, and background and ambient sound from the distant party. I can hear everything on iPhone 4, but much of the sound is dropped by iPhone 5. I’ve found a way to reliably reproduce the problem, perhaps useful for showing Apple the problem we’re having. Use Apple’s headset. Call from a very quiet location. Place a call to a call center’s greeting recording, ideally one that’s long and recorded at a varying volume, not too loud. I used Hertz On Demand here in the U.S. Set the volume to the lowest setting (important). Turn on mute. On my iPhone 5, the sound cuts in and out on 100% of the calls on every iPhone 5 I’ve tried, whereas everything is clear (though quiet) on my iPhone 4. The Genius bar had the same experience with their iPhone 5. I think the guy at this link has the best graphic demonstration of the problem: http://www.iphone5callquality.com/measurements/. You can clearly see what the phone is doing – it is discarding quiet signals. Unforunately, that includes entire words and phrases, especially if you've got the volume set low. I want to hear everything, don’t you?

One report says it is fixed in 6.1. Other fixes are dropping LTE or enabling hearing aid mode (that doesn’t work with headset though).

In my testing I switched back and forth between an iPhone 4 and iPhone 5 on a single conference call. The effect was pretty dramatic. I think it gets more pronounced after the first 6-15 seconds of a call. It feels like some kind of audio compression or background noise cancellation gone bad. Curiously, I think I can hear better when I'm on a call in my noisy van with lots of background noise at my end.

Several reports claim disabling LTE helps, though my understanding is that on AT&T's network voice always uses 3G, LTE is data only. Others say 'hearing aid mode' clears the problem up for non-headset use, but has no effect on headset. One developer reported that 6.1beta fixes the issue, another than a full factory default reset helped. Others claim improvements with a replacement phone, and many have no trouble at all. WiFi on/off doesn't make any difference. Several report problems are site specific. iPhone 5 to 5 connections are  the worst.

On the other hand, there really aren't that many complaints overall. Most users seem to be unaffected.

I suspect it's a combination of certain phone serial numbers/chipsets with certain networks. It might be fixable by a software update or a true fix might require a phone replacement. I've scheduled an Apple Store appointment and I'll share what I learn here. If the store doesn't know of an issue I'll hold off on a repair/replacement.

I've tried the 'LTE off' "fix", but since AT&T uses 3G for audio I doubt that will work. I have also tried the 'Hearing Aid' fix -- I can imagine that would help with non-headset calls. If it does I'll avoid the headset for a while.

See also: iPhone 5 Call Quality problem.

Update: from the Bouwmeester site: "HUGE NEWS from Apple Ireland: 'Your #iphone5 call quality issue is real, the next iOS version will solve it.'  but then:  "Apple: 'There MIGHT be a solution for the #iphone5 call quality issue in the next iOS but it is not guaranteed."...

Update 12/11/12: I had tolerable results both at my office and during the drive home using my Apple earbuds. Compared to my home the primary differences are different cell towers and more background noise. I don't think LTE settings make any difference for me. I do have 'hearing aid enabled' set but I doubt it makes any difference and, in any case, it's supposed to have no effect when a headset is used. I did try Settings:Reset:Resest Network Settings (you will need to reenter your wifi pw).

FWIW, I submitted a report to AT&T via email.

Update 12/12/12: I visited the local apple store, and, unsurprisingly, they hadn't run into this problem. The staffer I worked with felt it probably wasn't a hardware issue, he was wondering about a problem related to the noise cancellation function. He thought the very quiet setting of my home calls was a more likely factor than my local cell tower. He also suggested a network setting reset - which I'd done. He also wondered if my Speck candy shell was influencing the behavior of the microphone used for noise cancellation -- I'll try a call without it.

The other thing I'll try is some background mood music we bought years ago for our then toddlers -- be interesting to see if that reduces voice clipping on the incoming calls.

Lastly, I'll try lying the phone flat during some calls so the rear noise canceling microphone is either face down on a sound absorbent surface or face up.

ssspluto had a good summary in a Discussion Group Post dated 12/12/2012 - 8:19am

Update 12/14/12: I think I've traced this about as far as I can, and there is a workaround pending an Apple fix

I've ruled out a number of factors contributing to the problems I experience. For the record, I am iPhone 5, AT&T, St Paul area and I use a wired headset (Apple and 3rd party). My problem is audio clipping on my incoming audio.

I don't think my problem is a hardware issue, though in modern complex devices there is a thin boundary between software and hardware issues.

There is really only one circumstance I run into SERIOUS problems, though there are subtle issues elsewhere: a conference call on our corporate Global Conference system when I'm at home. I can connect to the same conference using an iPhone 4S and I get the normal (mediocre) sound quality of a VOIP based conferencing system.

Here are the things that don't seem to matter:

• LTE on or off
• WiFi on or off
• Case on or off
• Position of phone
• Covering or uncovering the rear background-noise-canceling headphone
• Resetting my network settings
• Model of wired earset/headset
• Restarting phone
• Background noise where I am

Here is what works

• unplug my headset when I've enabled 'hearing aid mode' and listen to the phone directly or use speaker phone.

I think there are multiple issues in this thread, but, as noted by a few contributors, this looks like an issue with the new-with-iPhone 5 noise cancellation software/hardware Apple is using and its interaction with AT&T's 3G compression in some cell towers.

The fix is 'hearing aid mode', which probably changes or disables noise cancellation when not using a headset. It is possible that a hardware problem on some iPhones is causing the noise cancellation product to misbehave, but since this is new software, and since for me the problem is so much worse with this one audio source and possibly even with selected cell towers, I'm somewhat optimistic it will be fixed with next iOS update.

I'm pretty sure Apple's engineers know what's wrong.

Update 1/9/13

The bug continues to annoy, but with the hearing aid setting I can do the problematic home-based Global Crossing conference calls on speaker phone or by old-fashioned handheld phone. In the meantime I read reports that the carriers know there's a problem, and one indefatigable Apple customer has a report from Amsterdam....

Yesterday I visited the Apple Store in Amsterdam to demo the call quality problem of my iPhone 5. Two employees from the Apple Store (an Apple Genius and a person from the Business department) made test calls with my iPhone 5 and had to admit that there clearly is a problem with the call quality. When you are on a call the incoming voice drops in and out, the audio sounds digitized and choppy.

We also tested my iPhone 4 with the same version of iOS (6.0.2). The call quality of the iPhone 4 was perfect. The Apple Genius decided to place more test calls with two of their own iPhone 5’s and experienced the same call quality issues. All test calls were made using the standard Apple EarPods.

To rule out that the problem could be caused by settings or installed apps, the person from the Genius Bar activated a brand new iPhone 5 for me. When we made test calls with this new-out-of-the-box iPhone 5 the result was the same: choppy sound on every call. The exact same effect that can be heard in my YouTube video.

The person from the Genius Bar concluded that this is a real problem that they cannot solve. He told me that he would do everything for me to find a solution for the problem and that I would hear from Apple soon. I hope that the Apple Store Amsterdam is more helpful than Apple Ireland.

 I was pretty sure Apple understood the bug and was working on a fix, but I am beginning to wonder ... 

Update 1/31/13

I think 6.1 fixed the problem I had, though I have yet to test from my home cell tower. I did a Global Crossing VOIP conference call from my car and it went well, I've seen other reports of success. I hope to test from my quiet home setting and home cell tower next week.