Kinh wrote:I paid an extra $40 for the master guy to do itunes optimize and it basically sounds the same only not as loud. Seems all he did was pull the volume knob down. To my ears there's nothing different here.
Ahah yeah, under the disclaimer that I'm not gonna pay Apple for the privilege of knowing what "Mastered for iTunes" precisely
means according to them, there's very little that can be different.
Upon receiving your master, Apple will subject it to lossy compression to reduce the file size (that's nothing to with audio compression, of course). Which type of compression matters little, as there's no magic: the quality of the results will always depend essentially on the result's bitrate (the more,the better, but the larger the file) and the amount of artifacts that may occur when reconstructing the original waveform since - unlike normal sampling - we actually lose information when we size-compress in a lossy way.
A third factor in Apple's compression - the psychoacoustic model it employs - might be a little different than mp3 but having taken Fraunhofer's guys three decades to get to a good result (and let's just say they were a little more genius than your average Apple genius ;-) ), I wouldn't expect it to be that much different.
So anything that is mastered to survive lossy compression, while maintaining good quality, must peak quite lower than 0dbFS
(to ensure that the waveform reconstructed from less information does not end up clipping), often a very audible -1dbFS is a good target; and be encoded keeping a substantial bitrate
(for mp3s... 320Kbps seems to be the magic number, where the resulting file is smaller but very hard to distinguish from the full PCM).
Perhaps one can go a little less heavy handed with the limiter, or simply master for loudness-normalization rather than peak-normalization.
That means that the result will, indeed, sound a little lower (or quite a bit lower if it's loudness-normalized). In absolute terms, of course - until you reach for the volume knob.
That's it. Apple are indeed good at making money out of thin air :D