TBC Specification Question

[WyoVideo]

I'm curious to know what my Datavideo TBC-1000 specification of 4:2:2 sampling rate means. What do those numbers stand for? And why are they important? (Assuming that they are.)

Thanks,

Ed

[gshelley61]

Here's a pretty thorough explanation for you:

http://en.wikipedia.org/wiki/YUV_4:2:2

[edDV]

I'm curious to know what my Datavideo TBC-1000 specification of 4:2:2 sampling rate means. What do those numbers stand for? And why are they important? (Assuming that they are.)

Thanks,

Ed

Informally, it means analog composite or S-Video Y/C is split (decoded) into digital Y, U, V components. 4:2:2 means the luminance is fully sampled and the chrominance components are half sampled. Without a sample rate specified, one can expect one of the following

4x or 3x subcarrier frequency (3.58MHz NTSC or 4.43MHz. PAL)
13.5MHz CCIR-601 rates (same as DV and DVD)

Historically, TBC's were first 3xfsc then 4xfsc* (14.4MHz) because it was easier to tie sample rate to multiples of the subcarrier clock. Today most chips are designed for CCIR-601 (aka D1) sample rates.

Consumer stand alone TBC boxes reprocess the signal back to analog. Then the process of decoding and sampling is repeated by the capture card. A better solution would maintain digital components in 4:1:1 (DV format) or serial 4:2:2 (SDI - SMPTE 279m) to the hard disk.

* 4fsc or 4x frequency subcarrier was the source of the 4:2:2 notation. CCIR-601 changed the luminance sample rate to 13.5 MHz for both NTSC and PAL but the 4:2:2 notation for Y U V sample ratio continued even though the relationship to subcarrier frequency was more complex.

[davideck]

And why are they important? (Assuming that they are.)

Since the TBC converts its output back to analog, its internal sampling structure is not that important. Many older professional TBCs sample at 4:1:1, which is more than adequate for consumer analog VCRs.

Other factors are more determinant of TBC image quality, such as the quality of the analog filtering, the timebase correction capability, etc.

[WyoVideo]

Thanks for those responses. That helps me understand some of what's happening in the process a little better.

I had looked all through the forum for such information and never thought to look it up on wikipedia.

Ed