To explore this, I switched to using Beyerdynamic DT 990 Pro over-ears with a high impedance of 250 ohms and found that the difference was obvious: the iPhone 4 and 4S were the only devices to provide sufficient volume in quiet recordings using these headphones.

ENGADGET: Smartphones for audiophiles: is the iPhone 5 more musical than its rivals?

Up until this week, this particular piece of circuitry was the title holder for "world's thinnest smartphone, " measuring in at 6.55mm thick. (The Alcatel Idol Ultra now claims this title at 6.45mm, although it's technically not on sale yet.) Despite the small package, it also professes to pack a hefty audio punch, boasting a pair of Beyerdynamic MMX 71 iE earphones and Cirrus Logic CS4398 DAC.

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