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Behringer DCX2496 digital X-over
Behringer DCX2496 digital X-over
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Old 18th December 2009, 02:35 PM   #2121
sendler is offline sendler  United States
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Originally Posted by MJL21193 View Post
So when I see comparisons between the output at -12db as opposed to 0db and how one sounds more "revealing" or "open" and that it all goes to hell in a handbasket when the level is adjusted digitally
Where did you read goes to hell in a handbasket? I think I wrote that with -12db digital volume control the sound is "just starting" to turn for the worse.
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Originally Posted by charlesp210 View Post
I think that in a properly controlled and blind test, neither you nor I would be able to tell the difference caused by 12db of digital attenuation under typical circumstances.
It's an easy test to do. Doesn't even involve soldering. Maybe just plugging some cables around and turning some knobs. Although, we see that the performance of the DCX is worse at full scale so it would be easier to observe my findings by using a dac with more consistent performance as I did.
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Old 18th December 2009, 10:53 PM   #2122
charlesp210 is offline charlesp210  United States
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Originally Posted by AndrewT View Post
That peak signal is ~0dBfs.
The average signal should be around 10dB to 20dB below that.
At around 1Vac output the DCX is clean enough, for most uses. It needs improvement for domestic/critical listening.
This is the signal that needs to be attenuated by a further 10dB to 30dB.
This analogue attenuation will reduce the signal and reduce the distortion and reduce the noise coming from the DCX.
I agree that the signal is "clean enough" around 1v output. So if that's all you need, it's fine. Actually, I need a bit more, reaching up to 3v RMS, and it's still fine, though could be better.

But if you take the existing DCX and apply 20dB analog attenuator to the output, now the DCX needs to put out 10v for you to get your 1v out of the attenuator. So by using analog attenuator, you are increasing the percentage of distortion in the output, because the percentage of distortion increases at levels above 1v coming out of the DCX itself, whether you are attenuating that voltage or not.

If you need 15dB or so of attenuation for some reason (though I can't see why, actually, perhaps you should explain why), you can just use the 15dB of digital attenuation provided for in the setup menu for each output. In most cases, unlike using an outboard analog attenuator, using the built-in 15dB of attenuation will be harmless, in my opinion. Whereas most likely the external analog attenuation will not be harmless.
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Old 18th December 2009, 11:09 PM   #2123
charlesp210 is offline charlesp210  United States
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Quote:
Originally Posted by sendler View Post
Where did you read goes to hell in a handbasket? I think I wrote that with -12db digital volume control the sound is "just starting" to turn for the worse.
It's an easy test to do. Doesn't even involve soldering. Maybe just plugging some cables around and turning some knobs. Although, we see that the performance of the DCX is worse at full scale so it would be easier to observe my findings by using a dac with more consistent performance as I did.
Sorry about the overstatement. I just see no reason why small amounts of digital attenuation should affect things for the worse, under the circumstances like I imagine. Not seeing any reason for it, I'm somewhat uninclined to put the effort into the sort of blind objective test that would be required to get me to believe otherwise. However, I am determined to show that under circumstances that are directly applicable to me, the digital attenuation that I am currently using does not result in reduced dynamic range. I use the digital output of a Sonos system, and control the volume by the digital volume control of that system, possibly using as much as 25dB of attenuation. Now if this works the way I think it should, if I attenuate by, say, 30dB, and then re-inflate 30dB through level controls in the DCX, there should be no change in measured dynamic range. I verified several years ago that Sonos does put out 24bit signal when it uses attenuation. So I think this should work, and I'll report results here though it is only partly related to the DCX itself.

How exactly did you do your test of digital attenuation?
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Old 19th December 2009, 12:37 AM   #2124
Pano is offline Pano  United States
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Behringer DCX2496 digital X-over
In my case with the DCX I run just a little trim here and there. But I also boost the outputs by 4dB. Why? Because once the input signal gets sliced into 2 or 3 parts, each output section is pretty low. Running +6dB is too much, the rogue peak gets thru here and there.

My volume control is done in the player. It's calculated at 32 bits, then reduced to 24 or 16 as I choose. I will admit that I have not done rigorous testing to find if digital volume in the player is better or worse than analog attenuation after the DAC. But I don't hear the difference right away. I mean it does not strike me. But it's worth further investigation.
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Old 19th December 2009, 04:04 AM   #2125
sendler is offline sendler  United States
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Originally Posted by charlesp210 View Post
How exactly did you do your test of digital attenuation?
Just to copy from my original post:
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Originally Posted by sendler View Post
Signal path is EAD T1000 transport> Belden 1701A RCA to RCA> SRC2496 upsampling to 24/88.2 and converting to AES> 1701A XLR to XLR>Direct out DEQ> 1701A XLR pin 3 open to RCA> 4K switched shunt style attenuators on the amp inputs> Modified Sure 2X100 amp> Nordost flatline Gold 12 8 feet wires> DIY Usher 2 way.
.
Comparing -12db digital attenuation/-4db analog attenuation to -0 digital/ -16db analog reveals a slight loss of resolution with the increased digital attenuation even though the attenuators present a slightly more favorable load to the source when at -4db.
I used the above set up by starting with -12 digital and selecting a loud listening level with the attenuators wide open at -4db which is as loud as they go. Increasing the digital to -0 and turning the attenuators down 12db, 6 steps, gives me the same listening level. Back and forth very easily. This test requires analog volume control between the dac and the amps so is easiest with passive cross speakers although the repeatability of 4 stepped attenuators would allow me to make the same test when running active which I haven't been doing often for the last few years as my main focus has been on trying different affordable amps 2 channels at a time. It would also be very easy with a Didden modded DCX providing the repeatable analog attenuation if anyone with one of those happens to be reading this.
.
I don't know if your scenario of comparing -15db digital into +15db digital with -0db digital into +0db digital is really the same thing. I might be able to try it with two DEQs so will let you know what I find.
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Old 19th December 2009, 06:42 AM   #2126
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by charlesp210 View Post
[snip]If you need 15dB or so of attenuation for some reason (though I can't see why, actually, perhaps you should explain why), you can just use the 15dB of digital attenuation provided for in the setup menu for each output. In most cases, unlike using an outboard analog attenuator, using the built-in 15dB of attenuation will be harmless, in my opinion. Whereas most likely the external analog attenuation will not be harmless.
Part of the problem is that the DCX has some 14dB gain in the analog output stage to make it compatible with pro levels. This is too high for home audio so indeed you have to either attenuate it in the digital domain (up to -15dB available) which in my experience is audible once you get below -6dB or so. Or you need to have some analog attenuation after the output, but because some of the distortion is caused in that 14dB analog gain stage, the analog attenuation doesn't lower that distortion, as you say.

The optimum solution is to get rid of that 14dB analog gain after the DACs. Lower distortion, no need for digital attenuation, no (or less) attenuation on the analog output.

One solution is the total removal of that output gain board and go with passive output to your power amps. I wrote an article about that for AudioXpress, using a passive filter. Other people have used a xformer here.
My final solution is a replacement output board with filtering and a 6-channel. remote control analog level control, although technically it is somewhat involved and not for everyone I guess.

But again, the optimum solution is to chuck that 14dB output gain on the DCX.

jd
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Old 19th December 2009, 01:07 PM   #2127
Pano is offline Pano  United States
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Behringer DCX2496 digital X-over
I agree with JD. Too much gain. And most of use don't need balanced, either.

Boy-o-boy, do we need a sticky or a wiki on "Gain Structure". So many of the problems reported for all sorts of gear on this forum simply come down to bad gain structure.
But would anyone read it?
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Old 19th December 2009, 04:37 PM   #2128
Brett is offline Brett
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Originally Posted by panomaniac View Post
But would anyone read it?
Probably not, and only a few of those who did would understand it.
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Old 19th December 2009, 05:22 PM   #2129
Pano is offline Pano  United States
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LOL!

Well, we like a challenge, right? Could we write one that most folks could understand? Maybe add pretty pictures and diagrams.
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Old 20th December 2009, 10:15 AM   #2130
pidigi is offline pidigi  Italy
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well, count me in, amongst the ones that will read it! And of course also amongst the ones that will not understand it completely

Ciao!

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