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Old 11th July 2013, 07:55 PM   #1
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Default Audio compressor to lower TV commercials-help needed

I want to make an AGC system to tame the sudden rise of volume in the TV commercials because recently my mother, a cardiac patient, is having problem with this sudden high output.

I googled a lot and found some circuits. I searched the fora too. But I am not sure about their performance/quality.

I tried to build a very well documented circuit that I found on http://construyasuvideorockola.com/proyect_normalizador.php

But despite my best effort, I failed to obtain the chip.

So could anyone guide me please with a good DIY alternative and tested circuit with easy to find parts ( and of course easy to build ) for my specific purpose? An experienced help will definitely save my hard earned money.

Any help is really much appreciated.

Thank you.
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Last edited by csom; 11th July 2013 at 08:10 PM.
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Old 11th July 2013, 09:49 PM   #2
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working under the assumption you have a separate amplifier and speaker system for the TV, I'd suggest that if you can find a used Behringer compressor/limiter (the limiter action being better here), you'd be all set. They are inexpensive new as well, so that might work out for you. Actually any pro audio compressor limiter will do the trick.

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Old 12th July 2013, 12:21 AM   #3
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Go to: THAT Corporation Audio Technology and find their app notes on the THAT2150/2180. If you like the part, I can send you a few of the 2150. PM me (and anyone else who would want some). The 2180 is a pre-trimmed part for minimum distortion, but for most applications the 2150 will do just fine. E
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Old 12th July 2013, 12:16 PM   #4
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Quote:
Originally Posted by bear View Post
working under the assumption you have a separate amplifier and speaker system for the TV, I'd suggest that if you can find a used Behringer compressor/limiter (the limiter action being better here), you'd be all set. They are inexpensive new as well, so that might work out for you. Actually any pro audio compressor limiter will do the trick.

_-_-
Thank you for the suggestion.
I will try to find one if I can.
Meanwhile I am looking for a DIY approach with easy to find parts.
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Old 12th July 2013, 12:23 PM   #5
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Quote:
Originally Posted by mickeymoose View Post
Go to: THAT Corporation Audio Technology and find their app notes on the THAT2150/2180. If you like the part, I can send you a few of the 2150. PM me (and anyone else who would want some). The 2180 is a pre-trimmed part for minimum distortion, but for most applications the 2150 will do just fine. E
I thank you for your very informative post and kindness.
I have taken a look on that site.

But today I found a circuit by Rod Elliot
http://sound.westhost.com/project53.htm
I have 2 TLO72 opamps in my stock. Perhaps I can give the project a try.

If the result is not satisfactory I might have to seek for your kind help.

Thank you very much.
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Old 12th July 2013, 12:35 PM   #6
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If anyone has a better DIY solution ( again I emphasize on the easily available components ) with a PCB Layout in PDF, kindly feel free to post here. That would be a great help.

Thank you.
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Old 13th July 2013, 05:44 PM   #7
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I don't understand how you intend to use this. You intend to tap into the audio path inside your TV set? Or is this something you can inline with a couple of phono jacks?

If you require an external device, I'd say definitely go the pre-packaged route, it'll save you a whole lot of trouble. This is going to be mono?

I would avoid the speaker method, however RNC makes a "really nice" optical compressor for cheap, there are a few others that would work nicely - and in a pinch you can even use a guitar pedal (which you can probably buy on Craig's List for 25 bucks or something).
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Old 13th July 2013, 06:09 PM   #8
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Originally Posted by nonsqtr View Post
I don't understand how you intend to use this. You intend to tap into the audio path inside your TV set? Or is this something you can inline with a couple of phono jacks?
Thank you for your input.
My TV system has no Auto volume leveller or Audio AGC.
The sound is being played through a stereo amplifier.

Quote:
Originally Posted by nonsqtr View Post
If you require an external device, I'd say definitely go the pre-packaged route, it'll save you a whole lot of trouble. This is going to be mono?
It would be better to have a stereo compressor / limiter.

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Originally Posted by nonsqtr View Post
.......there are a few others that would work nicely - and in a pinch you can even use a guitar pedal .
Could you post some DIY reference?
Guitar pedal is a manual solution I guess. I need an automatic leveller.

Quote:
Originally Posted by nonsqtr View Post
.....(which you can probably buy on Craig's List for 25 bucks or something)
I have no online shopping facility in my village or the place where I reside ( like many other countries) .
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Old 14th July 2013, 11:15 PM   #9
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Originally Posted by csom View Post
Could you post some DIY reference?
Sure. Compressors - the easiest solution is to put either a FET or an LDR across the input, and control it with the output. Here's a simple example with a FET: http://www.electroschematics.com/wp-...-schematic.gif

The FET acts as a variable resistor, and it's pretty easy to control with a voltage that you can derive from your output, by rectifying (with a diode) and integrating (with a capacitor). You can use an LDR too, but then you need a mechanism to control your light-emitting diode (or light bulb, whichever you're using).

The tricky part of this is that the compression is usually in the linear range, so for instance, you have a "compression ratio", say 10:1 or something. So this arrangement, based on what you've said, isn't going to "limit" your output level, it'll only give you "slightly less change" in level for a large change in input. It sounds like what you want, is an actual LIMITER, which is basically a compressor with an infinite ratio.

In the circuit above, T2 is normally driven in the linear range, but if you bias it just right you can probably get something approximating a true limiting behavior.

And, this is mono - for stereo, what they usually do is "couple" the side chains, so that if your L is loud it'll compress both your L and R, so the overall ratios stay correct. (The "side chain" is the control signal, basically in this case the connection between T2 and T1). So, if you build two of these and you succeed in biasing them into the threshold (limiting) range, you can try putting a small resistor between the two channels, or a resistor-and-capacitor, right at the point where T2 and T1 meet.

Someone can jump in here with exact details, or a better idea, but in my view this is about as simple as it gets, and if you're willing to play with the component values a little you can probably come up with something that works.
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Old 15th July 2013, 07:16 AM   #10
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Get rid of the amplifier and for your personal music, use headphones. You can buy a stereo tranmitter for transmitting the audio to an FM personal stereo and personalize.

Some audio content, even if you like, from the TV is a headache for the other, even normal humans.

Gajanan Phadte
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