Expander inserted between AV receiver and amp - AVS Forum
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post #1 of 18 Old 04-01-2013, 12:11 PM - Thread Starter
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Hi, I'm new to the forums and I would like to know if anyone has tried the following before and their thoughts on it:

In an attempt to increase dynamic range of the movies I'm playing I inserted a set of expanders between the AV receiver and the amplifiers. The idea of a downward expander is to set the threshold above the loudest signal and to set an expansion curve greater than 1:1 So with a 2:1 curve a -2dB signal would be attenuated to -4dB for example. A -4dB signal to -8dB and so on. A downward expander will not increase the signal above its treshold, so a very loud sound will not be amplified even further.

Note that an expander will not fix your noise floor issues. garbage in = garbage out

I am using the following equipment:
  • Yamaha RX-V771
  • Behringer DI800 (to convert the RCA preouts to balanced XLR)
  • 2x Behringer XR4400
  • 3x Behringer EPX4000 (5x400W at 8ohm and 1x1400W at 2ohm for the sub)
  • 5x home built speakers and home built sub
  • Optoma GT750 and 3D-RF glasses

I must say I am impressed with the result. The biggest effect is noticed on the LFE channel. Explosions on screen made my jaw drop to the floor. I realize that allot of people on this forum have much better equipment and may laugh when they read my list. I am just interested on hearing some reactions on the idea of putting expanders in the signal chain of a home theater setup.
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post #2 of 18 Old 04-01-2013, 02:10 PM
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I have absolutely no idea what you're talking about...what's an "expander"? Got a link?
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post #3 of 18 Old 04-01-2013, 02:35 PM - Thread Starter
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This is the expander I am using: http://www.behringer.com/EN/Products/XR4400.aspx

An expander is the opposite of a compressor, it increases volume differences in a signal where a compresser tries to reduce it. A upward expander makes loud noises louder, a downward expander makes quiet sections ever quieter. The Behringer XR4400 is a simple and cheap downward expander, normally you use these things when recording in a studio to reduce background noise. But you can use them on your whole signal by setting the threshold just above your loudest peak signal instead of just above your noise floor.

Some links with more info I picked from a google search:
http://www.sae.edu/reference_material/audio/pages/Compression.htm
http://www.mediacollege.com/audio/processing/expansion/
http://varietyofsound.wordpress.com/2011/01/19/compressor-gate-and-expander/

Imagine you are watching a movie and there is a quiet part followed by a very loud sound like an explosion. With an expander the difference between the loud and quiet part of the movie will be much bigger. This is a very different effect then simply turning the volume knob up on the amplifier which makes everything louder.
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post #4 of 18 Old 04-01-2013, 02:59 PM
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Hmmm...interesting.

But....in my system, I really don't need more of a difference between the loud and quiet parts - just one recent example; when that bomb went off in Zero Dark Thirty during the dinner scene in the hotel, I about jumped outa my chair! biggrin.gif

If that bomb was any louder I think my wife would be done with me and this whole home theater business. wink.gif
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post #5 of 18 Old 04-01-2013, 03:25 PM - Thread Starter
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Good point. I did get noise complaints using this setup. smile.gif

I have to turn the whole thing off at lower volume levels because quiet parts of the movie become inaudible with it. But at higher volume levels it is a very useful tool for me. Before I tried this, I could feel my ears getting tired from the constant high volume. (listener fatigue?) Now I can watch movies and 99% of the time the volume is at a comfortable level for me. And the other 1% it still rattles the whole house like I want it to.
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post #6 of 18 Old 04-14-2013, 09:12 PM
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During the analog-audio period of LaserDisc, Pioneer released a 3-band expander to expand the dynamic range of the soundtrack. With the current audio dynamic range, dynamic range expander is no longer needed.

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post #7 of 18 Old 04-14-2013, 10:35 PM - Thread Starter
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This is not a technical issue like back then. This is an attempt to restore some dynamics lost due to over usage of compressors. It is not perfect but for $200 worth of cheap gear it did help with listener fatigue on over-compressed content.
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post #8 of 18 Old 04-19-2013, 01:28 AM
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Hmmm, my Denon 4520CI has this option for compressed content IIRC, like Internet radio. I use it on that, however for other content no I don't use it.

You can adjust how much expansion to apply, at the high level and even mid level the bass does seem overly emphasized, so I leave it on the lowest setting. If off then Internet radio does sound lacking dynamics.

For full range dynamic content material then this would also overemphasize the low end too much, as its not been compressed right?


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post #9 of 18 Old 04-19-2013, 05:52 AM
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All recording have somekind of dynamic compression applied, especially in vocals. Even when you're listening at live concert, as long as they are miked, there will be some form of dynamic compression applied.

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post #10 of 18 Old 04-19-2013, 06:49 AM
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ALL recordings??? That is certainly not true.

In general, no compression is ever used when recording classical music, even a full orchestra. Mercury made a big point of stating explicitly that all of their recordings were done with no limiting or compression.

Your experience must be limited to "pop" music.

I have personally been involved in recording sessions for jazz music, both at live venues and in-studio, and no compression was ever used.



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Originally Posted by David Susilo View Post

All recording have somekind of dynamic compression applied, especially in vocals. Even when you're listening at live concert, as long as they are miked, there will be some form of dynamic compression applied.
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post #11 of 18 Old 04-19-2013, 08:12 AM
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Originally Posted by commsysman View Post

ALL recordings??? That is certainly not true.

In general, no compression is ever used when recording classical music, even a full orchestra. Mercury made a big point of stating explicitly that all of their recordings were done with no limiting or compression.

Your experience must be limited to "pop" music.

I have personally been involved in recording sessions for jazz music, both at live venues and in-studio, and no compression was ever used.

RIAA (records) and NAB (tape) equalization is analog compression and expansion. Dolby and DBX took it to the next level. So at least all analog formats used compression and expansion albeit not in the same context as being discussed here..

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post #12 of 18 Old 04-19-2013, 08:26 AM
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Originally Posted by Alan P View Post

I have absolutely no idea what you're talking about...what's an "expander"? Got a link?

These devices were quite popular in the 1970s and into the 80s. DBX was the primary manufacture of these units. There are usually tons of them on EBAY. They made 10s of different models over the years. CD basically obsoleted these devices but many still use them including me. They are great for old recording and soundtracks but you should not use them with modern digital recordings. Most units have a bypass switch of some sort.

Like anything in nature you don't get something for nothing. The problem with this technology is "breathing" or "pumping". If the expansion is pushed too hard the VCA (Voltage Controlled Amplifier) will hunt which causes the breathing and pumping. It's due to the fact the detection circuits have to analyze the incoming signal then adjust the gain with the VCA. Problem is by the time the signal is measured, it is already through the VCA and the gain change applied may have little or no relation to the signal currently flowing through the VCA. With 1970s analog technology you could not delay or store the signal - at least not at a consumer price point, and basically not at a professional price point either.

Now today it would be a piece of cake to build a near perfect expander as we can easily delay and store the audio signal and apply processing precisely at the right instance in time. All this for a few dollars worth of chips. But then the same technology that allows our near perfect expander also enables us to make near perfect recordings without dynamic range limitations in the first place.

Hence there is little interest and market for such a device today for consumer playback.

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post #13 of 18 Old 04-19-2013, 09:25 AM
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fwiw, from my 4520CI manual, like I posted above I only use this for Internet Radio and then on low setting...
4520%2520Restorer.JPG
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post #14 of 18 Old 04-19-2013, 09:30 AM
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Quote:
Originally Posted by mtbdudex View Post

fwiw, from my 4520CI manual, like I posted above I only use this for Internet Radio and then on low setting...
4520%2520Restorer.JPG

there's a difference between data compression (lossy encoding) and dynamic compression (changing the dynamics (loud-to-soft) of the recorded item. WHatever restorer does for lossily encoded material, it has nothing to do with dynamic compression.
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post #15 of 18 Old 04-19-2013, 08:07 PM
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And those restorer are actually only preset EQ.

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post #16 of 18 Old 05-07-2013, 12:43 PM - Thread Starter
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Quote:
Originally Posted by mtbdudex View Post

For full range dynamic content material then this would also overemphasize the low end too much, as its not been compressed right?
When I set the receiver crossover to 80Hz, the LFE channel does get too loud compared to the other channels. However I am using full-range speakers and when I disable the crossover in the receiver the low-end sounds fine. Just that everything below 80Hz now comes from every speaker instead of the woofer.
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post #17 of 18 Old 05-07-2013, 01:00 PM - Thread Starter
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Quote:
Originally Posted by Glimmie View Post

Like anything in nature you don't get something for nothing. The problem with this technology is "breathing" or "pumping". If the expansion is pushed too hard the VCA (Voltage Controlled Amplifier) will hunt which causes the breathing and pumping. It's due to the fact the detection circuits have to analyze the incoming signal then adjust the gain with the VCA. Problem is by the time the signal is measured, it is already through the VCA and the gain change applied may have little or no relation to the signal currently flowing through the VCA. With 1970s analog technology you could not delay or store the signal - at least not at a consumer price point, and basically not at a professional price point either.

Now today it would be a piece of cake to build a near perfect expander as we can easily delay and store the audio signal and apply processing precisely at the right instance in time. All this for a few dollars worth of chips. But then the same technology that allows our near perfect expander also enables us to make near perfect recordings without dynamic range limitations in the first place.
Note that the Behringer XR4400, when you enable the expansion mode of the gate, the timing controls are disabled and the gate goes into a zero-attack mode. (<10 µsec)
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post #18 of 18 Old 05-08-2013, 07:20 AM
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Quote:
Originally Posted by VTOLfreak View Post

Note that the Behringer XR4400, when you enable the expansion mode of the gate, the timing controls are disabled and the gate goes into a zero-attack mode. (<10 µsec)

Yes, that box has peaked my interest. The Behringer stuff is low cost as well. I in fact use their digital crossover on my system. Works very well for me.

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