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Old 29th August 2012, 04:58 PM   #1
puppet is offline puppet  United States
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Default Automatic Line level Attenuation Circuit

System set-up ... CD-player ----> -10/+4 interface ----> digital processor ----> amp ----> speakers

Does a diy solution exist for resolving the following issue:

When playing cd's .. various era's have differing output levels (+/-3-4db). While the -10/+4 interface and the digital xo have input level controls ... it get's to be a PITA adjusting the levels for the various program materials. I also have people here that can't be bothered with monitoring levels. CD-player has no attenuation control.

I'd like to set the system gain and forget it. Putting an automatic device between the cd and the interface would accomplish that. Looking for something that I can set gain with and have it automatically attenuate higher cd output levels without user intervention. Not looking for fancy .. just simple.

Last edited by puppet; 29th August 2012 at 05:01 PM.
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Old 29th August 2012, 05:02 PM   #2
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You'd probably found something for that at THAT Corporation, AGC (Automatic Gain Control). Depends on how experienced you are with cobbling together a diy version, but the ICs and app circuits are available from them.

jan didden
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Old 29th August 2012, 05:09 PM   #3
puppet is offline puppet  United States
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I read up on that a little bit earlier today. Seems that what I'm after might not be that involved?

RDL has a device that sounds like what I'm after but I'm not too sure. It's a pretty small package .. but at $250 I was hoping that there might be a diy equivalent.
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Old 29th August 2012, 08:53 PM   #4
AndrewT is offline AndrewT  Scotland
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AGC were in all mic circuits used by the Ham radio operators.
They are also inside every car radio and all FM radios.
The AGC circuits were implemented with just a few transistors and other very cheap components. You could build a two channel version for a few $. Make sure the two channels track each other.
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Old 30th August 2012, 03:28 AM   #5
puppet is offline puppet  United States
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My understanding of an AGC is that it dynamically adjusts the level ... for this application that won't be optimal. I don't want the program material adjusted ... just the global level of it.

Thinking this through ... I don't believe what is needed can be fabricated. It should function as a shelving circuit when a given cd would redline the digital xo ... then release the shelving on a disc that won't redline <---- problem: without a cue on disc this action would be subjected to/by program transients. Unacceptable.

I see a switchable L-pad in my future.
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Old 30th August 2012, 03:58 AM   #6
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Quote:
Originally Posted by puppet View Post
System set-up ... CD-player ----> -10/+4 interface ----> digital processor ----> amp ----> speakers

Does a diy solution exist for resolving the following issue:

When playing cd's .. various era's have differing output levels (+/-3-4db). While the -10/+4 interface and the digital xo have input level controls ... it get's to be a PITA adjusting the levels for the various program materials. I also have people here that can't be bothered with monitoring levels. CD-player has no attenuation control.
<snip>
I tool my old low level CDs, ripped them, adjusted the audio levels and burned new discs. Adobe Audition can do wonders - almost miracles.

G
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Old 30th August 2012, 09:08 AM   #7
AndrewT is offline AndrewT  Scotland
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Puppet,
a gain block/ buffer at your pre-amp does what you want, but not automatically.

Set the gain to +0dB, or +6dB, or +12dB. That covers the range of inputs from CDP @ ~2Vac down to 500mVac.

You could add +18dB (250mVac) if you needed a really sensitive input for very low level gear.

That buffer gain block can be at your listening seat. The buffer can then drive long cables, 3m to 20m if that long is necessary, to reach the Power Amplifier/s attached to the back of your speaker/s.

You can set the steps as large or as fine as suits you and your gear. Steps of 2dB or 4dB or 10dB. Just select the resistors to suit the gain block topology.
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Last edited by AndrewT; 30th August 2012 at 09:11 AM.
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Old 30th August 2012, 09:22 AM   #8
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Quote:
Originally Posted by puppet View Post
My understanding of an AGC is that it dynamically adjusts the level ... for this application that won't be optimal. I don't want the program material adjusted ... just the global level of it. .
It might work if you gave it a very long time constant like several seconds. But yes, you don't want it to follow the program level envelope.

jan
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Old 30th August 2012, 06:27 PM   #9
Davey is offline Davey  United States
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The procedure offered by stratus46 seems the only solution to this issue.

To "normalize" played back material on-the-fly in real-time would be impossible. You need to rip the music into a suitable editing program like Audition, Goldwave, Audacity, etc, etc and then analyze the tracks to determine the increase in levels to achieve 0dbFS on the loudest peaks. Then adjust and save it.

Even then, should a person normalize each track of an album this way (with possibly different normalized levels) or evaluate the entire album and increase each track only by the (same) amount it took to normalize the highest recorded level track?

Cheers,

Dave.

Last edited by Davey; 30th August 2012 at 06:32 PM.
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Old 31st August 2012, 01:05 AM   #10
puppet is offline puppet  United States
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Originally Posted by Davey View Post
The procedure offered by stratus46 seems the only solution to this issue.

To "normalize" played back material on-the-fly in real-time would be impossible. You need to rip the music into a suitable editing program like Audition, Goldwave, Audacity, etc, etc and then analyze the tracks to determine the increase in levels to achieve 0dbFS on the loudest peaks. Then adjust and save it.

Even then, should a person normalize each track of an album this way (with possibly different normalized levels) or evaluate the entire album and increase each track only by the (same) amount it took to normalize the highest recorded level track?

Cheers,

Dave.
I've pretty much assumed that the engineer and the artist has covered the disc's content ... as far as dynamics go .. most of the time. Shouldn't need to go track by track adjusting levels. ... and I haven't run into a situation were that is required anyway. Ripping and normalizing everything is an option ... a daunting one :P

Thanks for all of your replies fellas ... much appreciated!
phil
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