From the 5th generation iPod on, Apple introduced a user-configurable volume limit in response to concerns about hearing loss. Users report that in the 6th generation iPod, the maximum volume output level is limited to 100 dB in EU markets. Apple previously had to remove iPods from shelves in France (French Lessons) for exceeding this legal limit
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The third generation iPod had a weak bass response, as shown in audio tests. The combination of the undersized DC-blocking Capacitors and the typical low-Impedance of most consumer headphones form a High Pass Filter, which attenuates the low-frequency bass output. Similar capacitors were used in the fourth generation iPods. The problem is reduced when using high-impedance headphones and is completely masked when driving high-impedance (line level) loads, such as an external headphone amplifier. The first generation iPod Shuffle uses a Dual transistor output stage, rather than a single capacitor-coupled output, and does not exhibit reduced bass response for any load.
