IPod the iPod Nano and Shuffle from its stores, marking the end of Apple producing standalone music players. Currently, the iPod Touch is the only iPod produced by Apple. 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
IPod Touch date has been introduced with the same release number of iOS as the contemporary iPhone model. Successive updates to iOS since the initial release in 2007 have released additional features. iPhone OS 2.0, released on July 11, 2008, introduced the App Store, which allowed third-party applications for the first time. iPhone OS 3.0, released on June 17, 2009, added features such as cut, copy, and paste, data tethering and push notification support. iOS 4.0, released on June 21, 2010, introduced iBooks, FaceTime, and multitasking. It dropped support for the first generation iPod Touch. In June 2011, iOS 5, the fifth