The Apple smartphones are equipped with noise reduction system, designed to improve sound quality when talking on the phone. The system allows to separate the useful signal from the noise outside sources, to give priority to voice. Without noise reduction the conversation in crowded places and transport, becomes a difficult task.
Hearing voices, the sound of wheels, rattling of the movable parts of the vehicle, and the sound of different instruments, spoil the conversation, making it illegible. With these negative phenomena and to fight the suppression of noise in the smartphone.
Active noise reduction in acoustic equipment
Active noise reduction system employed in audio equipment, it was inadequate to correct the sound in the course of conversation, said Mobcompany. Such systems are not tuned to the frequency of the human voice, able to distinguish the sound of the wheels of the subway train, the buzzing of the instrument, wind noise, etc. But they are unable to distinguish the words of one person from another when talking in a public place, or where a loud song, the mechanism will not be able to distinguish the voice of the speaker on smartphone.
The analysis of the frequency spectrum chip active noise cancellation can (not necessarily) just to weed out the signal, whose frequency corresponds exactly to the voice. Such, for example, are waves at frequencies below 50 Hz and above 5 kHz. If weed (or mute) inclusions of other frequencies. “on the side” will not hear the sound of the mixer, or the whistle of the kettle. And if they hear, it is very quiet. Since frequency is not enough to highlight the desired voice among the others, the second microphone is necessary.
How does the noise reduction system
An alternative way of noise suppression when the conversation began the use of additional microphones. They are located at a distance from the main, on the rear panel or the bottom.
Due to spatial diversity is the main microphone during the conversation picks up user’s voice is stronger than the subsidiary. That, in turn, more receptive to ambient noises, as it is located farther from the mouth of the subscriber. Chipset smartphone (or a dedicated ADC for processing the audio signal from the microphone, analyzes the frequency spectrum with both microphone channels. Using a special algorithm, it is possible to distinguish the user’s voice from noise in software.
In the process, the sound processor iPhone analyzes the spectrum of acoustic waves received from different microphones. The one that is considered the main priority, and is a kind of “standard”. The mechanism of noise suppression “studies” volume of sounds at different frequencies to identify the most intense. Since the main microphone is placed closer to the mouth than other sources – most pronounced is the conversation. Comparing the “picture” from the first MIC that the first chip determines what sounds the microphone picks up the auxiliary stronger than the main. They are considered to be noise, and the suppression mechanism suppresses or decreases the volume of tones at these frequencies.
Noise reduction system with three microphones
In the latest generation iPhone, starting with models 5, 5s and 5c is used just three microphones. This is done in order to improve the efficiency of the noise reduction system. Getting surround sound, the sound chip can more accurately determine which acoustic frequencies belong to the subscriber (and require strengthening, and what third-party sources (and their need to drown). This approach improves the quality of communication, but makes the phone more expensive, and so is rare.