Greater loss of bitrate when converting from 256 kbps AAC to 128 kbps AAC

in iPod + iTunes + AppleTV edited January 2014
Hi everyone,

I had over 800 MP3s of various bitrates which I converted to 256 kbps AAC format in iTunes, in order to standardise them all, then deleting the originals. However, I was then told by a friend that if I simply reconverted the new ones to 128 kbps but still saving them in AAC format, I would save on half the disk drive space. Since memory is at a premium on my computer, I did just that but the results in iTunes show that the songs have since turned out in various different bitrates again, ranging from 99 kbps to 103, 105, 107, 123 etc. The settings in Preferences are as I left them, AAC Encoder with High Quality (128 kbps). I realise that this is not such a big issue in terms of listening and playback but I am curious as to why iTunes has decided to dictate the individual bitrate for each song despite my settings. Any comments or feedback would be much appreciated, thanks!


  • Reply 1 of 1
    banchobancho Posts: 1,517member
    You took a lossy format (MP3) and converted it to a different lossy format (AAC) and regardless of the bitrate, lost some quality. You then reconverted from the initial lossy format to a lower bitrate of that same lossy format. I'm not entirely sure why the bitrates vary as you say. Didi you have VBR selected by any chance? How much space did the initial batch of MP3s take up? I wouldn't think you'd recover that much space converting to AAC's. They are smaller on average, but not by a large margin.

    I think your biggest problem is the repeated conversions where you're losing quality along the way at each step.

    For my own use I leave files in the format I get them in unless I've got the source to use for re-encoding.
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