LE BLOGGLOSE

Recueil cinématographique

1000 Hz - 13 000 K | 31 octobre 2009

1000 Hz (Son)

1KHz

Signal de référence utilisé pour calibrer à l'aide d'une seule source, un appareil où une chaîne complète de traitement ou d'enregistrement sonore.

On utilise pour vérifier aussi le 400 Hz et le 10 000 Hz lors d'un calibrage complet et qualitatif de cette chaîne.

1000/1001 (Conversion vidéo - Analogique)

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Anglais :

The nominal 30 frames/60 fields per second of NTSC color television is usually multiplied by 1000/1001 (= 0.999) to produce slightly reduced rates of 29.97 and 59.94 Hz. This offset gives rise to niceties such as drop-frame timecode (dropping one frame per thousand – 33.3 seconds) and audio that also has to run at the right rate. Although having strictly analog origins from the very beginning of NTSC transmissions as a fix-it to avoid a clash of frequencies, it has also been extended into the digital and HD world where 24 Hz becomes 23.97 and 30 frames/60 fields per second are again changed to 29.97 and 59.94 Hz. Of course, as the frame/field frequency changes, so do the line and color subcarrier frequency as all are locked together. Note that this does not apply to PAL color systems as these always use the nominal values (25 Hz frame rate).

The reason for the 1000/1001 offset is based in monochrome legacy. Back in 1953, the NTSC color subcarrier was specified to be half an odd multiple (455) of line frequency to minimize the visibility of the subcarrier on the picture. Then, to minimize the beats between this and the sound carrier, the latter was to be half an even multiple of line frequency, and to ensure compatibility with the millions of existing monochrome TV sets, the sound carrier was kept unchanged – at 4.5 MHz – close to 286 times the line frequency (Fl). Then, in a real tail-wags-dog episode, it was decided to make this exactly 286 times... by slightly altering the line frequency of the color system (and hence that of the color subcarrier and frame rate). Interestingly it is said that the problem could soon have been solved with a little improved engineering, so avoiding the need for this awkward frequency offset and all the many thousands of hours of additional engineering and operational effort this has caused down the years.

Here’s the math.

Fl = frames per second x number of lines per frame
Nominally this is 30 x 525 = 15,750 kHz
But it was decided that:
286 x Fl = 4.5 MHz

So Fl = 4,500,000/286 = 15,734.265 kHz
This reduced Fl by 15734.265/15750 = 1000/1001 or 0.999
As all frequencies in the color system have to be in proportion to each other,
this has made:

NTSC subcarrier (Fl x 455/2) = 3.579 MHz
30 Hz frame rate (Fl/number of lines per frame) = 29.97 Hz

Following on, all digital sampling locked to video is affected so, for example, nominal 48 and 44.1 kHz embedded audio sampling becomes 47.952 and 44.056 kHz respectively. As reasons for ‘drop-frame’ are analog it is not an inherent requirement of digital television. So with maybe with the US analog switch off on 17 February 2009 we can start ditching drop-frame?

1080 60P (Format HD)

1080 lignes en mode 60 images pleines (Progressif)

1080I ou 1080i (Format HD)

Résolution 1080 lignes à balayage entrelacé (i)

"i" pour intrelaced

Il s'agit du format le plus couramment utilisé en haute définition.

Il correspond à 1 080 lignes et 1 920 pixels par ligne, avec un balayage entrelacé. Mais la mention 1080I à elle seule ne permet pas de spécifier la fréquence d'images,
pouvant être 25 ou 30 Hz, selon les normes SMPTE ou UIT, ex: 1080i50 ou 1080i60, pour 50Hz en Europe et 60Hz aux Etats-Unis.

1080P ou 1080p (Format vidéo)

Format d'image TV de 1 080 par 1 920 lignes, avec balayage progressif.

La fréquence d'images peut être 25 et 30 Hz, comme pour le 1080I, mais également 24, 50 ou 60 Hz.

1366, Socket (Informatique - Carte mère - Processeur)

Socket 1366

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1440p (Format vidéo)

Capteurs pour le HDV entre autre.

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1800 K (Eclairage)

Température de couleur rendue par une bougie.

1920x1080 (Ecran - Format - Résolution)

Résolution des écrans HDTV-1080, anciennement dénommés "Full HD".

13 000 K (Eclairage)

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