I've got a music collection of lossy M4A files at assorted bitrates that I want to transfer to my iPhone, and in order to conserve space I want to make each track as small as possible while keeping the quality of it indistinguishable from the original on my computer. I took a small portion of the collection (30 files) and re-encoded each one to two different bitrates to test: 128kbps and 192kbps (what I've been using up till now without any noticeable lack of quality from the originals).
As far as I can make out, the 128kbps files sound exactly the same on my computer as the 192kbps files do, so I'm considering making all of the music on my iPhone 128kbps, but I'm worried about whether these files will sound the same when I transfer them to my iPhone 5.
Is it at all possible that my 128kbps M4A files will play at lower quality on the iPhone? Is the iPhone's playback quality a common bottleneck when it comes to music playback, or will it be able to play 128k files - or any other bitrate, for that matter - the exact same as on my computer? Just wondering whether others have similar experiences on this that could help me make a decision here.