Earlier phones employed various methods to achieve noise suppression, but newer smartphones like the iPhone 4 use two microphones—one to listen to the speaker's voice and another to listen to ambient sounds like street noise. The first microphone is situated at the bottom front of the phone near the speaker's mouth; the second is located on the top edge of the phone. Software in the phone's audio chip set creates a profile of the ambient sounds detected by the second mic, and then subtracts that aural profile from the sound picked up by the mic near the speaker's mouth. The result is a phone call that, at the other end of the line, sounds as though the caller were calling from a land line in a quiet room.
Since people rarely use cell phones in quiet rooms, noise suppression technology is an important feature.
Removable Storage: MicroSD Cards
SD (Secure Digital) cards and their smaller MicroSD and MiniSD memory-card cousins are the types of removable storage commonly used in portable and wireless devices to store data such as video, music, and image files. The main difference between standard SD, MicroSD, and MiniSD cards is their size. According to iSupply, most cell phones that shipped during 2010 used the smallest of the three card types, MicroSD.
If you're planning to store a large quantity of large media files (such as video) you may want to choose the largest-capacity card that your device will accommodate. The capacities of the MicroSD cards used in most cell phones range from 2GB to 32GB. The 2GB cards retail for less than $10; 16GB (Class 4) cards commonly sell for around $50; and 32GB cards can run as high as $150.
The SD Association has established various speed classes for SD cards. These classes represent the minimum speeds required to write various types of data to the card. Following are the most common speeds, together with the types of content they support, according to the SD Association.
Class 2 : H.264 video recording, MPEG-4, MPEG-2 video recordingClass 4: MEPG-2 (HDTV) video recording, DSC consecutive shootingClass 6: Megapixel DSC consecutive shooting, professional video cameraClass 10: Full HD video recording, HD still consecutive shooting
Gyroscope vs. Accelerometer