TV Sound Circuitry

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Robert Reed
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TV Sound Circuitry

Post by Robert Reed » Sun Jan 17, 2016 12:05 pm

I purchased a LG 42" TV a couple of years ago and as expected the sound quality is horrible. I was told I needed an opto coupled "sound bar" to get better audio. This just sticks in my craw, that after dropping $500 for a TV and now they want $2-300 to get decent sound out of it.
So after while of listening to this garbage sound, I decided to see if there was just a simple audio output jack buried in that jungle of rear panel connectors - nada! But there was a headphone jack that I found and tried it. Sound was still lousy. Next I connected my Hi-Fi system to it and although there was considerable improvement but it was still below the bar.
Now the big question- Does the opto coupled audio for sound bars come from the same location as the head phone audio? I am thinking if it was further upstream and taken from a purer source that maybe the sound quality would be better. My dilemma is that installing a sound bar and getting audio from the same general location as the headphones there would be no improvement. As the saying goes "Garbage in-Garbage out".

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Janitor Tzap
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Re: TV Sound Circuitry

Post by Janitor Tzap » Sun Jan 17, 2016 1:44 pm

Robert,
Have you seen this?
http://conversation.which.co.uk/technol ... -32lm620t/


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Robert Reed
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Re: TV Sound Circuitry

Post by Robert Reed » Sun Jan 17, 2016 6:44 pm

Thank you for the link. My TV falls smack dab in the target range here as being a year 2013 model, so I will pursue this with the phone numbers given. Then I will wait to see if an "engineer" shows up to repair it. I don't hold much hope of any success for two reasons: customer service never delivers and the problem they supposedly fix is to "cushion" the speaker some how. This would mean that the amplifier is still performing poorly even after the so called FIX. There is one thought still swimming around in my head. Do you remember from years ago when the Asians developed what they called the 'integrated speaker amp'. This was developed for the myriad of tiny portable transistor radios being produced at that time with even tinyer speakers. The idea behind it was to distort the amplifier out put in such a way as to compensate for the distortion in the crappy speakers. I'm getting dejavu in relating this to my TV.

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VernGraner
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Re: TV Sound Circuitry

Post by VernGraner » Mon Jan 18, 2016 4:36 pm

Robert Reed wrote:Does the opto coupled audio for sound bars come from the same location as the head phone audio?
The answers is tricky as it seems to be both YES and NO depending upon how you look at it. :smile: To explain-

By necessity, the headphones audio out is analog. It would be created by decoding the digital audio stream from the TV channel to an analog audio stream, then sending it through a small amplifier to the headphones. Essentially:

Digital audio from TV channel->D/A Converter->Small amp->Headphone jack

If you use the optical out, you are skipping the internal D/A and the little amplifer which allows you to do this:

Digital audio from TV channel->Optical output ->External High Quality D/A Converter->High Quality Amp->Headphone jack

So, though both of those have the same "source" (the TV channel audio) the quality of the Digital to Analog converter and the quality of the headphone amplifier play a very large role in the quality of the source you are hearing.

In my system, I use the optical jack (TOSlink) to connect my TV to an external surround sound receiver. The Digital to Analog converter in the receiver (a a Denon AVR-1613) is not only high quality, it is capable of separating the audio into discrete surround channels. So, rather than just having just a "left " and a "right" as you would get from the headphone jack, I get Front Right, Center, Front Left, Right Rear, Left Rear and Subwoofer outputs. This creates a number of advantages for great sound:
  • The Receiver's amplifier section has considerably more power than the amplifier built into the TV
  • The speakers I use with the receiver have considerably better frequency response and sq inches of cone to move the air
  • I have the ability to adjust the center channel up or down to increase the volume of the dialog
  • I can turn the subwoofer output down at night so I don't wake the house when things in the show explode :grin:
  • The headphone jack on the front of the receiver uses the better D/A and amplifier section so it sounds much better than the TV headphone jack
  • I have the ability to use the EQ in the receiver to compensate for the moderate high-end hearing loss I have (too much rock n roll in the 70s!) :cool:
  • The receiver has a microphone that can be used to do a complete spectrum analysis of the room and compensate for resonance, reflections, and phase problems caused differing speakers distances to your preferred listening site
  • The Receiver has the option of enabling a "Normalizer" that acts as an automatic gain control to keep commercials from blaring too loud and gunshots/explosions from blowing you out of your chair :shock:
As a side note, when I do use headphones with the receiver, I can go to a much higher volume and take advantage of the EQ and normalization functions of the amp as well. :grin:

As you might be able to tell, I am a big fan of using an external receiver for the audio part of TV viewing. :)

I hope this helps you figure out what to do about the sound situation you have. :)

Vern
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Robert Reed
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Re: TV Sound Circuitry

Post by Robert Reed » Mon Jan 18, 2016 6:24 pm

Thanks for clarification Vern. If I read you right, you are saying:
1) Head phone jack has its own demodulator (digital to analog) and audio amp.
2) Sound bar takes audio (in digital form) from a different location in the sound chain.
3) Sound bar then performs the basic tasks as the TV headset jack does
except to a much superior level and with a lot more options.

You didn't mention the TV internal sound system to the speakers. I assume that audio power is attenuated and drives the headset Jack-correct?

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VernGraner
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Re: TV Sound Circuitry

Post by VernGraner » Tue Jan 19, 2016 8:30 am

Robert Reed wrote:Thanks for clarification Vern. If I read you right, you are saying:
1) Head phone jack has its own demodulator (digital to analog) and audio amp.
2) Sound bar takes audio (in digital form) from a different location in the sound chain.
3) Sound bar then performs the basic tasks as the TV headset jack does
except to a much superior level and with a lot more options.

You didn't mention the TV internal sound system to the speakers. I assume that audio power is attenuated and drives the headset Jack-correct?
I really don't know if newer sets have separate "headphone" audio amps. In older systems, they would use a "switching" headphone jack and an attenuation system for the headphone jack that provided the proper load to the amp output to keep it operating properly. So essentially, yes. :grin:

I just know I was a *lot* happier with having a completely separate audio system that allowed me a lot of control of the sound. :)

Vern
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