Eth (Ð, ð; also spelled edh or eð) is a letter used in Old English, Icelandic, Faroese (in which it is called edd), and Dalecarlian. It was also used in Scandinavia during the Middle Ages, but was subsequently replaced with dh and later d. The capital eth resembles a D with a line partially through the vertical stroke. The lowercase resembles an insular d with a line through the top.

The letter originated in Irish writing (Freeborn 1992, 24) as a d with a cross-stroke added. The lowercase version has retained the curved shape of a medieval scribe's d, which d itself in general has not (but see for instance the Audi logo).

In Icelandic, ð represents a voiced dental fricative like th in English "them"; however, the name of the letter is pronounced eþ, i.e., voiceless, unless followed by a vowel. It has also been labeled an "interdental fricative.

In Faroese, ð isn't assigned to any particular phoneme and appears mostly for etymological reasons; however, it does show where most of the Faroese glides are, and when the ð is before r it is in a few words pronounced as [g]. In the Icelandic and Faroese alphabets, ð follows d.

In Olav Jakobsen Høyem's version of Nynorsk based on Trøndersk, the ð is always silent and is introduced for etymological reasons.

In the orthography for Elfdalian, the ð represents a voiced dental fricative like th in English "them", and it follows d in the alphabet.

In Old English, ð (referred to as ðæt by the Anglo-Saxons) was used interchangeably with þ (thorn) to represent either voiced or voiceless dental fricatives. The letter ð was used throughout the Anglo-Saxon era, but gradually fell out of use in Middle English, disappearing altogether by about 1300; þ survived longer, ultimately being replaced by the modern digraph th by about 1500.

The ð is also used by some in written Welsh to represent the letter 'dd' (the voiced dental fricative).

Lower-case eth is used as a symbol in the IPA (IPA), again for a voiced dental fricative, and in IPA usage, the name of the symbol is pronounced with the same voiced sound, as /ɛð/. (The IPA symbol for the voiceless dental fricative is θ.)

Computer encoding

• In the Unicode universal character encoding standard, upper and lower case eth are represented by U+00D0 and U+00F0, respectively. These code points are inherited from the older ISO 8859-1 standard. In HTML, eth is represented by the Latin character entities Ð and ð.
• On UNIX-like systems such as Linux it can be entered with the Compose key plus d and - or D and - for the uppercase version when using ISO8859-based locales or Compose key plus d and h or D and h for uppercase version when using UTF-8-based locales.
• Using Microsoft Windows, one can hold Alt while typing 0208 or 0240 on the numeric keypad to produce the uppercase and lowercase forms, respectively. The US-International keyboard layout allows the letter to be entered by holding AltGr and pressing the letter "d."

Miscellaneous

• The letter ð is sometimes used in mathematics and engineering textbooks as a symbol for a spin-weighted partial derivative. This operator gives rise to spin-weighted spherical harmonics.
• The modern Greek letter delta (Δ, δ) has, in general, the same phonetic value, and ð is the only Latin alphabet letter faithfully representing delta's phonetic value. (In Ancient Greek delta represented a d sound).
• The symbol is mentioned in the Rush song By-Tor and the Snow Dog in the first verse:

Prince By-Tor takes the cavern to the North light,
The sign of Eth is rising in the air.

References

• Freeborn, Dennis (1992). From Old English to Standard English. London: MacMillan.

See also

• D with stroke
• African D
• Insular script

External links

• How to make the Eth
• Förslag till en enhetlig stavning för älvdalska (March, 2005)

The SD-SDI transmitter calculates two CRC values for each video field--one corresponding to the active picture, and corresponding to the entire field (excluding the switching lines)--and places them in an EDH ancillary data packet. The EDH packet is inserted at a specific location in each field of video. The SD-SDI receiver also generates the same two CRC values for each field and compares them against the CRC values in the received EDH packet to determine if each field of video is received without errors. The EDH packet also contains bits to signal that a prior link in a broadcast or transmission chain contained an error; equipment which receives a video signal with an incorrect CRC, and retransmits the signal, is expected to re-insert the correct CRC (which may be different if the equipment alters the video signal in any way) and set the flag indicating a prior error. This feature makes it easier to determine which link, in a multi-link chain, was the source of the error.

The EDH protocol does not provide for error correction, only error detection. Also, there is no mechanism in SD-SDI to allow a field containing errors to be retransmitted. EDH is used primarily to assist in identifying faulty equipment in a video chain so that it can be quickly replaced or repaired.

EDH is not used with high definition video, as the HD serial digital interface includes a mandatory embedded CRC for each line.

The SD-SDI EDH protocol is defined by SMPTE RP 165-1994 and the equivalent ITU standard ITU-R BT.1304

See also

• error detection and correction

External links

• Error detection and handling in digital television
• An Error Measurement Method for Television
• Society of Motion Picture and Television Engineers: Recommend Practice 165-1994: Error Detection and Handling. Available for purchase at the SMPTE website