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Topic: quality of amazon and itunes mp3s (Read 18201 times) previous topic - next topic

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  • Kohlrabi
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quality of amazon and itunes mp3s
Reply #25
I just wanted to say that you compare AAC (M4A file from iTunes) and MP3 (from Amazon). And yes, AAC spectrograms usually look better.

Some MP3 V0 spectrograms are better than AAC 256...
And some girls are bigger than others. And some girls' mothers are bigger than other girls' mothers.

Joking aside, spectrograms convey no information whatsoever about the quality of a lossy encoder. As long as the bought files are artifact free, I really don't see why any user needs or should care about the encoder settings used by an online shop. I doubt that shops care about users who want to transcode files, and I'd say users wishing to do so should buy lossless media in the first place.
  • Last Edit: 21 October, 2012, 01:18:42 PM by Kohlrabi
It's only audiophile if it's inconvenient.

  • [JAZ]
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quality of amazon and itunes mp3s
Reply #26
@Blutarsky: From your post and replies to what others told you, it is clear that you don't know several things about MP3, (and several others about iTunes Store).

First, that MP4/AAC (which is what iTunes Store has always used) is not the same as MP3. (Second post in this thread already explains it).
Second, that you don't know how to judge quality in terms of lossy codecs.
And third, you don't know the limitations of the MP3 codec, and how LAME has been tweaked these last years to increase in sound quality, while not caring about "visual" quality.

See your posted graph:
- The differences in background from 16Khz above are at -95dBFS and below.
- The filter in MP3 is at 19Khz and in AAC at 21Khz. Said that, filtered sounds are around -70dbFS and below.
- Peaks on that sound are at -30dbFS or so.

- MP3 has a limitation at 16Khz and above that can cause to use many bits to keep precision, reducing the amount free for the rest of the sound (which is not desiderable). As such, LAME limits the precision in these bands. That's why you see the clear 16Khz background cut.
- Also, higher frequencies are always more difficult to encode, because they are not tonal (easy to describe), but noise-like (difficult to describe).
Using the filter around 20Khz (which most CD audio players were supposed to do anyway) is just another way to reduce the bits spent on frequencies that the human ear doesn't hear (most of the time), to spend them on the rest of the bands.

As such, from those spectograms, one cannot say that the MP3 one is of less quality in terms of lossy codecs. One can only say that they use a different strategy, which in the case of AAC/MP4 can do so because it does not have those MP3 limitations.

  • Porcus
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quality of amazon and itunes mp3s
Reply #27
It strikes me that perceptual noise substitution is A Good Thing In That It Keeps Users From Judging Sound With Their Eyes.