I'm not surprized, if mp2 at 224kbps be better than mp3. It has to be so in theory.
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"What theory would that be?"
MP3 has a much more efficient encoding structure than MPEG Layer 2. This doesn't magically change at high bitrates.
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Sorry for being late with the answer, but now after guruboolez posts I could only add the citation from well known paper “MP3 and AAC Explained”:
5.6. Bit-rate versus quality
MPEG audio coding does not work with a fixed compression rate. The user can choose the bit-rate and this way the compression factor. Lower bit-rates will lead to higher compression factors, but lower quality of the compressed audio. Higher bit-rates lead to a lower probability of signals with any audible artifacts. However, different encoding algorithms do have ”sweet spots” where they work best. At bit-rates much larger than this target bit-rate the audio quality improves only very slowly with bit-rate, at much lower bit-rates the quality decreases very fast. The ”sweet spot” depends on codec characteristics like the Huffman codebooks, so it is common to express it in terms of bit per audio sample. For Layer-3 this target bit-rate is around 1.33 bit/sample (i.e. 128 kbit/s for a stereo signal at 48 kHz), for AAC it is around1 bit/sample (i.e. 96 kbit/s for a stereo signal at 48 kHz). Due to the more flexible Huffman coding, AAC can keep the basic coding efficiency up to higher bit-rates enabling higher qualities. Multichannel coding, due to the joint stereo coding techniques employed, is somewhat more efficient per sample than stereo and again than mono coding...
MPEG layers were designed to provide sufficient sound quality and the same time to be efficient in their area of application. For the reason sweet spot of mp1 (384-448 kbps) provides better audio quality than sweet spot of mp2 (192-256 kbps), which is better again than sweet spot of mp3 (112-160 kbps). Due to slow improvements in sound quality at bitrates above sweet spots, there are points where previous layer begins to provide better audio quality (AAC is going to be an exclusion from this rule – time and tests will show). For mp3/mp2 such point is between 224 and 256 kbps.
So, using layers at higher than sweet spot bitrates is inefficient and could be reasonable for compatibility only.