Is it really necessary to still use 75% amplitude for television anymore? - AVS Forum
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post #1 of 4 Old 05-15-2013, 12:32 PM - Thread Starter
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I would really like to ask a question on this forum: is it still necessary to follow that guideline for 75% picture amplitude with today's technology? I was hoping that someone could have an answer to this question.

The guideline for 75% picture amplitude (instead of 100%) originates from the NTSC system, when they thought it was necessary to prevent overloading and overmodulating in the TV. The guideline continued with the ATSC HD TV system and the FCC requires it. By the way, I know that they use 100% amplitude in international TV systems.

But, I am wondering if they still need to be concerned with overmodulating and overloading in the TV with today's digital TV technology.
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post #2 of 4 Old 05-15-2013, 01:19 PM
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It was never necessary, but when you only have one control, it's best to center where you adjust the range.

So yes it's still recommended.

Joel Barsotti
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post #3 of 4 Old 05-15-2013, 08:01 PM - Thread Starter
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I see. And I think that the picture at 75% amplitude does look nice.
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post #4 of 4 Old 05-15-2013, 08:19 PM
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The use of 75% color bars with analog NTSC was to prevent overmodulation of the OTA transmitter. The largest value that can be transmitted is 120 IRE (which corresponds to 0% AM modulation). But the level of both the yellow and cyan 100% bars is 130.8 IRE.

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