Dynamic Range Compression on Cable TV not working

Discussion in 'General Electronics Chat' started by Stanly, Mar 31, 2014.

  1. Stanly

    Thread Starter New Member

    Mar 29, 2014
    22
    0
    Hi everyone,

    Actually, I submitted this questions yesterday, but then I mistakenly left the "thread subscription" as "do not subscribe." So I don't know what the responses were.

    So here I go again.

    On three of my four televisions, the Dynamic Range Compression does what it is supposed to do. That is, it makes the strong signals (in the higher channels) a little softer, and the weaker signals (in the lower channels) a little louder.

    But on my fourth TV, just the opposite is happening. If I leave Dynamic Range Compression to "heavy," then the upper channels are too strong and the lower channels are too weak. Setting Dynamic Range Compression to "none" improves the situation. So, on this one television, the DRC does just the oppositie of what it should do.

    All the other cable settings on my four TVs seem to be identical.

    Does anybody have any ideas as to what is happening?

    Thank you.

    Stanly
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    Dynamic range compression of what signal? Are you talking about the sound?
     
  3. Stanly

    Thread Starter New Member

    Mar 29, 2014
    22
    0
    Hi crutschow,

    Yes, the sound.

    Stanly
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,042
    3,243
    Dynamic range compression of the sound minimizes the sound level change between the loudest and softest sounds so, for example, you can turn down the volume so as not to disturb someone else while still hearing the soft sounds. It has nothing to do with the high and low channels or their relative RF signal level. That's taken care of by the RF AGC circuit which you have no control over.

    Why do you think the higher channels have a stronger signal than the lower channels?
     
  5. Stanly

    Thread Starter New Member

    Mar 29, 2014
    22
    0
    Hi crutschow,

    Well, all I know is that the channels from the 500s come in louder than the channels in the 100s.

    In any event, however, on this one television the dynamic range compression is not compressing the range of volumes. But the dynamic range compression is doing so on my other three televisions.

    Why, I wonder.

    Stanly
     
  6. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    Maybe 3 of your TV's have a compressor in them and one doesn't.
     
  7. Stanly

    Thread Starter New Member

    Mar 29, 2014
    22
    0
    Hi #12,

    Thank you for your response.

    I am reluctant to ask this, but here goes:

    What is a TV compressor?

    Can I find out if my TV has a compressor?

    Stanly
     
  8. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    You have stated that your question is about the loudness of sound. There are ways to compress audio signals so that the loudest sound comes out only a little louder than the weaker sounds. Signetics used to make a chip called NE570. It could compress or expand an audio signal. There are many other ways to make a sound compressor. I wouldn't be surprised if some people did it with software. That is, a computer program that replaces the NE570 chip. You wouldn't be able to find that in a schematic and the manufacturers of your TVs probably wouldn't even speak to you about how or whether they have an audio compressor in a certain television.
     
  9. Stanly

    Thread Starter New Member

    Mar 29, 2014
    22
    0
    Hi everyone,

    So the thought occurred to me to do the following experiment:

    I took the TV that doesn't seem to be compressing the sound and put it on one of the cable lines where the compression is working as expected.

    Lo and behold! The previously troublesome TV is compressing the sound correctly. So the problem is not with the TV after all, but with that particular cable line.

    Does anybody have any thoughts, please?

    Thank you.

    Stanly
     
  10. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    Get the cable TV company to make all the cables deliver the same quality.
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    If the cable is at a very low signal strength, the compressor will have cranked the gain right up and will not vary the gain. So it will behave as if the compressor is "not working".

    So you could have a high impendance cable, or a low signal strength coming from the source (before the cable).
     
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