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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 16th December 2013, 12:37 PM   #1
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Default Stereo + LFE (2.1)?

By scanning the web I concluded this is a rare yet simple approach, very untapped niche market to say the least!
Apart from crappy all-in one 2.1 packages normally in the form of cheap desktop solutions, by manufacturers like Logitech. That and car-sub crossovers.
Unless Google is filtering my results it's strange that something as important as this, at line level is virtually non existent.

Problem is I cant find something that splits stereo into 2.1, software or hardware.
On the software side, 5.1 plugins exists but always never accommodate 2.1 because programers always assume you have additional Center and Surround L+R speakers, meaning if you only have stereo you miss out on half the stereo image due to surround algorithms used for 5.1. Even Quad stereo is more prominent than 2.1. what gives? We all know bass is omnidirectional, so we only really do need one calibrated sub.


If there was such a solution, hardware or software, how does summing from stereo to mono actually work (I've always wondered since setting up my car system, which sound like a$$ what a waste of money lol)... Is it just a case of reversing phase 180 to balance the driver between the stereo drivers? Or is it more complicated? Obviously it exists for 5.1, which is largely kept inward, either deep in programing or inside HT receivers I think its called LFE/AC3 decoding or something)

Doing 2.1 digitally first makes sense. If properly implemented should allow more control over filters and x-over points.
My on-board motherboard sound has a 2.1 feature however though with limited control and bad SQ.

Some sub-woofers have crossovers in them to allow full range to pass through and output stereo minus bass, which is essentially all I need to go to a pair of speakers.
The sub-woofer I would like to use, does not have Outputs

Any thoughts?

Last edited by giro1991; 16th December 2013 at 12:43 PM.
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Old 17th December 2013, 11:55 AM   #2
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Quote:
Originally Posted by giro1991 View Post
By scanning the web I concluded this is a rare yet simple approach, very untapped niche market to say the least!
Apart from crappy all-in one 2.1 packages normally in the form of cheap desktop solutions, by manufacturers like Logitech. That and car-sub crossovers.
Unless Google is filtering my results it's strange that something as important as this, at line level is virtually non existent.

Problem is I cant find something that splits stereo into 2.1, software or hardware.
On the software side, 5.1 plugins exists but always never accommodate 2.1 because programers always assume you have additional Center and Surround L+R speakers, meaning if you only have stereo you miss out on half the stereo image due to surround algorithms used for 5.1. Even Quad stereo is more prominent than 2.1. what gives? We all know bass is omnidirectional, so we only really do need one calibrated sub.


If there was such a solution, hardware or software, how does summing from stereo to mono actually work (I've always wondered since setting up my car system, which sound like a$$ what a waste of money lol)... Is it just a case of reversing phase 180 to balance the driver between the stereo drivers? Or is it more complicated? Obviously it exists for 5.1, which is largely kept inward, either deep in programing or inside HT receivers I think its called LFE/AC3 decoding or something)

Doing 2.1 digitally first makes sense. If properly implemented should allow more control over filters and x-over points.
My on-board motherboard sound has a 2.1 feature however though with limited control and bad SQ.

Some sub-woofers have crossovers in them to allow full range to pass through and output stereo minus bass, which is essentially all I need to go to a pair of speakers.
The sub-woofer I would like to use, does not have Outputs

Any thoughts?
The hardware is available . You can score an Emotiva UMC-1 for about $ 350 second hand with plenty of warranty left and that does the job with a lot of tweaking freedom ( and A LOT of other features) . Although I have no experience (yet ) with minisDSP I think it can be done with one pretty easy .In a DIY way , place a couple op Op-Amps , in your L and R channels , Low pass filter the signals , sum them with an other op amp , and there you go .

Cheers ,

Rens
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Old 17th December 2013, 04:23 PM   #3
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Quote:
Originally Posted by giro1991 View Post
Problem is I cant find something that splits stereo into 2.1, software or hardware.
An analog subwoofer filter can do what you want. Some plugins will provide the same function, but that's more of an effect than high fidelity music. And it's harder to adjust.

[/QUOTE]On the software side, 5.1 plugins exists but always never accommodate 2.1[/QUOTE]

Strange. The very first plugin Google located offers 2.1 down mixing. And every other Dolby AC3 plugin I know does. Have a look:

Free Download AC3 Filter 2.6b : AC3 Filter is a DirectShow filter for AC3 decoding


[QUOTE]because programers always assume you have additional Center and Surround L+R speakers, meaning if you only have stereo you miss out on half the stereo image due to surround algorithms used for 5.1. Even Quad stereo is more prominent than 2.1. what gives? We all know bass is omnidirectional, so we only really do need one calibrated sub.

I don't know about any quadro plugins. Care to share those?

Quote:
If there was such a solution, hardware or software, how does summing from stereo to mono actually work
Summing L and R will give you mono. Lowering the level 6 dB will correct the resulting gain.

Quote:
Is it just a case of reversing phase 180 to balance the driver between the stereo drivers? Or is it more complicated? Obviously it exists for 5.1, which is largely kept inward, either deep in programing or inside HT receivers I think its called LFE/AC3 decoding or something)
If you reverse phase, you'll get L - R or R - L. Not mono.

BTW there's nothing secret or magical about Dolby AC3. On the contrary, it's all very well documented. After all, Dolby Labs wants everybody to sell as many tools and content as they can, since they get a couple of cents with every sale.

AC3 decoding is used to decode the compressed Dolby AC3 stream and split it into 8 independent channels.

Quote:
Doing 2.1 digitally first makes sense. If properly implemented should allow more control over filters and x-over points.
It doesn't. 2.1 as such doesn't even exist in Dolby AC3 country. It's just a way to easily hear all channels over a normal stereo setup. The failure of the surround system lies mainly in the WAF, if you ask me. 6 loudspeakers and their associated cabling is just too much for most spouses.

What you want is really very easy, either in the digital or in the analog domain.

In the analog domain, just add front and rear channels with some resistors. Add sub channel with lowpass filtered output from L and R. Almost a straight forward stereo sub setup.

This leaves out the center channel, which isn't necessarily used for music. But that leads to the question what you'll be using it for. If it's for surround with movies you will also need to mix the center to both main channels. And that -might- sound awful.
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Old 18th December 2013, 10:40 AM   #4
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Cheers a bunch for the response peeps
Emotiva is great but it's a tad overkill
Quote:
Summing L and R will give you mono. Lowering the level 6 dB will correct the resulting gain.
ah, this has been bugging me for a while actually, i thought it would have been more complex.
So adjusting gain on a sub is the same thing really, though finding 6dB would require a calibration mic.

The AC3 app I will try, strange I could not find it.

Quote:
I don't know about any quadro plugins. Care to share those?
I use foobar as my music player. There is a dsp called, 'convert stereo to quad stereo' for it, if you used it in a chain before another dsp 'xover' (see below) this would force xover dsp to accept 4 channels (defined by quad dsp) and then configure outputs accordingly using ASIO compatible outputs. Only problem with this approach is it's limited to music playback, so no video. :/

Here is what I've tried so far
I tried configuring a downloaded dsp with variable filters called foo_dsp_xover but I can't get it to out put 2.1 because it converts into surround sound like I said.
Click the image to open in full size.

I also found this. It does what I want exactly.
It's only the trial version however is restricted to foobar/vst/music playback.
Click the image to open in full size.

I will get an analogue xo at some point in time but I needed something to do me until I make one so wanted to explore alternatives.
Was looking for the Elliot Sound Productions 3-way, could not find it and found this instead, which is ideal considering its adjustable, unlike the ESP.
Linkwitz DIY Crossover

Continuation/thoughts welcome
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Old 19th December 2013, 02:18 PM   #5
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I've tried lots of different configurations using the xover dsp and the thing is uterlly useless unless you have surround left and surround right, depends on recording but some instruments sound distant no matter what.

Still configuring AC3 decoder...

Slightly off topic now but... can I use thiells-small given by a manufacturer of a woofer to determine the best xo point for it?Click the image to open in full size.
100hz to 1k looks steady so an xo at around 100hz -3 down would make sense i'm guessing. (my whole life is a guess lol)..

Any good ref. CD's to calibrate phase at xo also? I know crossover for the sub and low region is critical so I would like to get it right first time I try it.

cheers
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