Re: how does video affect audio in broadcast?

[edDV]

If cable video is too hot, nothing will blow up. It will just cause analog audio to buzz when video weights toward whites.

This was in the post you made for the guy trying to convert mpeg 2 to dv for a community broadcast.

How does the video format impact the audio in a broadcast? I would have assumed they would be independent of each other. Usually for home projects it is. I mean if you screw up your video or your audio its one or the other not both that go screwy.

Is it something to do with the actual broadcast mechanism itself? THis is interesting, I would like to know..... (or post a link if you don't have time to describe it yourself ).

Video and audio are separate at baseband (composite, S-Video, YPbPr, etc.) but to broadcast over TV or cable the video and audio are modulated into a 6MHz RF signal where audio is FM modulated just above AM modulated video and the Quadrature modulated color subcarrier.

Luminance can interfere with color and audio if the amplitude or high frequencies interact with color (crosscolor) or audio (distortion). Color can also interfere with audio. That is why NTSC uses 29.97 MHz frame rates to minimize color harmonic interference with audio.



In a frequency plot, you can see luminance, chominance and audio sharing the same 6MHz RF channel.



More tech stuff here
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3551


PS: This is why you often see video and audio problems on community access, education or government cable channels where minimal tech specs apply. They just play whatever they are given. Broadcast stations are much more picky about what they will accept.

[yoda313]

Thanks eddv! Very educational.

[Squash]

Yeah, thanks. I've seen this occur occasionally for at least a couple of decades. Always wondered if my TV was screwed-up.