i just want to know which is better, purchased itunes store aac vs. normal itunes ripped aac?
does the quality differ?
iTunes software's own ripping engine probably isn't as 'secure' as EAC, dBpowerAMP or CueRipper, for example. That's probably more important than the AAC encoder, especially at 256 kbps or so.
Also, you control which release you rip (for example Dark Side Of The Moon comes in about 4 or 5 versions, some with more dynamic range compression than others, and you can choose the one you prefer).
The AAC encoder used by iTunes Store was issued by Apple in their "Mastered for iTunes" initiative, I believe, for mastering engineers to be able to test the destination format, so you could compare that against a 256 kbps encode in your version of iTunes.
Itunes plus is the same exact thing used in the itunes store to encode.
Except for mastered for itunes titles which take the high resolution files and they are carefully downsampled and abxed to minimalize the impact of audio compression *not sound compression*
Except for mastered for itunes titles which take the high resolution files and they are carefully downsampled and abxed to minimalize the impact of audio compression *not sound compression*
You cannot be sure anything was done carefully or that anything is ABXed. Furthermore the idea that people are tweaking the audio beyond preventing unwanted audible clipping in order to minimize coding artifacts is quite dusturbing. Claiming to have done so should instantly raise suspicion of ignorance as well as incompetence.
If “Mastered for iTunes” is anything more than a marketing spin (an open question, to be polite), then my first hunch would be that the substance is a “stop sending us these £$€& mp3s” request to the record companies and managements. Remember that there are quite a few “iTunes exclusive” tracks, in which case they need more than ready-mastered fileset which was put on CD. Oh, it could be some volume adjustment too, but that might possibly even be for the worse.
CD rip will contain dither that will (depending on the signal) take some of the bitrate to be encoded. Apple recommends that masters for iTunes are 24 bit undithered so theoretically the encoder spends more bits encoding actual HF signal rather than dither.
I'm not claiming this is audible or impacts perceived quality. I just say the resulting AAC files in many cases will be different.