44,100 Hz

In digital audio, 44,100 Hz (alternately represented as 44.1 kHz) is a common sampling frequency. Analog audio is recorded by sampling it 44,100 times per second, and then these samples are used to reconstruct the audio signal when playing it back.

44.1 kHz audio is widely used, due to this being the sampling rate used in Compact Discs, dating back to its use by Sony from 1979.

History

The 44.1 kHz sampling rate originated in the late 1970s with PCM adaptors, which recorded digital audio on video cassettes, notably the Sony PCM-1600 (1979) and subsequent models in this series. This then became the basis for Compact Disc digital audio (CD-DA), defined in the Red Book standard (1980). Its use has continued as an option in 1990s standards such as the DVD, and in 2000s, standards such as HDMI. This sampling frequency is commonly used for MP3 and other consumer audio file formats which were originally created from material ripped from Compact Discs.

Why 44.1 kHz?

The rate was chosen following debate between manufacturers, notably Sony and Philips, and its implementation by Sony, yielding a de facto standard. The technical reasoning behind the rate being chosen is as follows.

Hertz

The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves.

One of the unit's most common uses is in the description of sine waves and musical tones, particularly those used in radio and other audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven.

Definition

The hertz is equivalent to cycles per second. In defining the second, the International Committee for Weights and Measures declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M =  0 and F = 3, M = 0 of the ground state 2S_1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz" thereby effectively defining the hertz and the second simultaneously.

2182 kHz

The radio frequency 2 182 kHz is one of the international calling and distress frequency for maritime radiocommunication on a frequency band allocated to the MOBILE SERVICE on primary basis, exclusively for distress and calling operations.

Transmission modes

Transmissions on 2182 kHz commonly use single-sideband modulation (SSB) (upper sideband only). However, amplitude modulation (AM) and some variants such as vestigial sideband are still in use, mainly by vessels with older equipment and by some coastal stations in an attempt to ensure compatibility with older and less sophisticated receivers.

Range

2182 kHz is analogous to channel 16 on the marine VHF band, but unlike VHF which is limited to ranges of about 20 to 50 nautical miles (40 to 90 km) depending on antenna height, communications on 2182 kHz and nearby frequencies have a reliable range of around 50 to 150 nautical miles (90 to 280 km) during the day and 150 to 300 nautical miles (280 to 560 km) or sometimes more at night. The reception range of even a well-equipped station can be severely limited in summer because of static caused by lightning.

6955 kHz

"6955 kHz" is the sixth episode of the third season of the American science fiction drama television series Fringe. It first aired on November 11, 2010 in the United States. The third season spent much of its time alternating between the prime and parallel universes, and "6955 kHz" was set in the former. The storyline followed the Fringe team's investigation into a numbers station that mysteriously gave its listeners amnesia, a case that ultimately ties to a doomsday device.

The episode was written by story editors Robert Chiappetta and Glen Whitman, and was directed by Joe Chappelle. Its broadcast took place on the Fox network, and according to Nielsen Media Research, an estimated 4.8 million viewers tuned in. Reviews of the episode ranged from positive to mixed, as some reviewers disagreed about the introduction of a "First People" mythology.

Plot

Fauxlivia, Olivia Dunham's doppelgänger from the parallel universe, continues to pose as Olivia as part of the Fringe division. The Fringe team is brought in on a case where several people, part of an online group attempting to decode the information sent by a numbers station, have been stricken with amnesia. They discover the station broadcasting the signal, finding its workers killed and a strange box connected to the broadcast equipment. They identify fingerprints on the box of a Joseph Feller, but his current location is unknown. Walter attempts to decipher the workings of the box, while giving hope to some of the affected people that they will get their memories back in time.