So I have been doing some searching of my own and have come up with a scenario where this bass distortion always happens.
As a preface to this I have to say that I have only adjusted the volume (in the options panel in iTunes) for a handful of albums that are characteristically mastered at lower levels than the rest. I have noticed that distortion occurs in the following circumstance: (I am using an iPhone 4 running iOS 5.0)
If I am playing music randomly through my library or a playlist and the playlist eventually reaches one of these "adjusted" songs the song will play completely fine at the adjusted volume. No problems. If, however, the song plays normally to the end and then moves on to an unadjusted track this subsequent track will be horribly distorted. Strangely this does not happen if I skip to the next track before the adjusted track has finished playing.
When the music becomes distorted the ONLY way to bring it all back to normal is to either skip to the next track or restart the phone.
Basically it seems like the iPhone music player, if allowed to play a song to completion (this also happens if I skip to near the end of the adjusted song and then let it finish playing and move onto the next track automatically) will somehow "remember" the volume adjustment applied to the previous track and this then "applies" it to the subsequent track resulting in horrible distortion.
I am not sure how to submit this report to Apple either, but I hope they can fix this because it is truly annoying. Perhaps this will help some of you guys out there too.
That is a good analysis, but for example I had all my songs with +100% and I got the distortion, didn't have to wait until a song without adjustment to hear it.
By the way, setting a high volume in my car also makes the distortion noticeable, so I discard my idea that it has something to do with the JACK output.
I understand what you mean and, as you said, you weren't observing the distortion for the same tracks at 100% volume increase before you upgraded to iOS 5.0. I'm not sure why this is in your case. In reality, if the tracks were actually just being "overdriven" to produce distortion you should have seen it before you udated as well.
So just to check - do you currently still have the levels set to +100% in the music options? You might want to check the files that are actually on the phone as well (through iTunes) because just syncing again will not update the music files on the phone to drop the levels back down again. I know this sounds like a really stupid suggestion and I'm not trying to be patronizing or anything! Alternatively, you could try wiping the music off the phone and the transferring it again through iTunes (making sure that the levels on the files are set to neutral 0%).
If that still isn't helping - I have found that reseting the phone (home button + sleep/wake button) will return the levels back to normal for me (until the same thing as I described above happens).
The only other thing I can think of (that is always the same thing everybody says) is to do a restore of the phone. I know this is a HUGE pain in the neck (particularly since you have to copy all your media back again)...
I'm sorry I can't be more help, as I have only observed this happening when switching between +100% and 0% songs...
Thanks, but I already managed to minimize the distortion by deleting all the songs and synchronizing them again without any volume adjustment.
However, the distortion is still there if I listen very carefully, or set the volume loud. I really hope Apple solves this in 5.0.1, the iPhone is not the same without good quality audio.
I have same problems as you all, but I already tried to restore, to delete all my music and put just 1 song with iphone 4 ios5 clean, and distortion is there. My mp3 are all set to 80%, with ios4 my iphone's volume was never higher in the slider than 70-80%, music was loud enough even in the metro.
now, with my iphone volume slider at 100% I still have low distorted music.
it's horrible, my iphone 4 with ios4 had crystaline music. It's one month I don't listen at all to music, i dont bear more than 1 song, i switch it off.
I am deeply dissapointed we need to find a fix, instead of a super quick ios 5.0.1.... or maybe the problem is in Itunes 10.5 ... who knows....
Unfortunately this is a bug in iOS 5. As far as we found out, the Sound Check volume level is not updated when the iPhone begins a new song (when playing song by song). Stopping and resuming the playback usually fixes that and the volume is updated to the correct level.
So apparently Sound Check is somewhat broken in iOS 5. Apple has to fix that as soon as possible. Please file a bug to Apple to speed this up.
I HAVE FOUND A FIX!!
I've been having exact same problem as other folk on here in that the sound on my iPhone 4S has been distorted when playing music. I thought iOS5.0.1 would have fixed problem but it didn't.
So by complete fluke it has to be said, I have found a fix - and it's simple!
Go to Settings > Music > EQ on your iPhone or iPad and select Bass Booster.
Now play a song and notice the difference! (You'd think by increasing the bass it would make the distortion worse, but it has completely the opposite affect!)
Hope this works for everyone! :)
All songs sound horrible, even those purchased from itunes - so not a burned format issue. I am not experiencing the "bass" issue others describe, but more that certain layers sound distant and garbled. This layer is typically the voice layer on most tracks. I have tried many settings adjustments suggested by others, but nothing corrects the layer distortion.
This issue renders iOS useless for iPod functionality. Please fix ASAP.
Update: Sound distortion appears to only be an issue when playing through the audio jack. Playing through the iPhone's built-in speaker does not reproduce the layer issue.