the m7 volume for the headphone is far superior to m8. I am using the player pro to play all my musics. The m7 sound is clear and crisp. however on the m8 I am not satisfy with the quality and volume of the m8. You can turn the volume all the way up and it would feel like something is missing. I wanted to return the m8 badly because of it. But then I tweak the EQ on Player pro and downloaded the virper4android and tweak the EQ on there also. Its still not as good as m7 but close to it. I still like my m8 because of the sd card but I wish the size would be between 4.3 or 4.7 inch. I'm using viperrom on both my m7 and m8.
If it doesn't sound like it for you, your unit must be bad... Or there's something wrong with your ears
My cousin's first unit from Verizon had something wrong with the speakers/amp and had to take it back. Sounded very distorted.
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