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Old 3rd February 2007, 08:09 PM   #1
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Default Behringer DCX2496 crackling when limiting

The DCX is fed with an AES/EBU signal at input A (UB40 - Higher ground).
Output 1 & 2 is fed to a mixer to be able to listen with a headphones.
Stereo link is on
The only settings for these 2 outputs are as follows:
Low pass filter: 20Hz But24
High pass filter: 200Hz L-R48
Limiter: ON, -20dB
Gain reduction is now around 2-4 dB

I can now hear a crackle at each bass punch in my headphones, located in the higher frequencies.
So each time the limiter works there are unwanted signals coming from the DCX.
When I lower the limiter threshold or give more input signal, so that the limiter applies more gain reduction, the crackle stays longer.
The longer the release time, the less crackle is audible.

Probable explanation:
At each bass punch the limiter comes on 'gradually' and releases 'gradually'. Because this happens digital, it probably happens in little steps of 0.1 or 0.01dB? It seems that these steps are audible. With longer release times (3s), less steps of gain reduction have to be taken in the same time amount, so less crackle is audible.

Are there other people that have the same experiences? Or did the same test?
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Old 6th February 2007, 07:15 AM   #2
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I told the problem to Behringer and they reply "It seems that your device is defective".

Because the unit performs normal (I think) and only has this issue when it's limiting, I don't think this is really a defective unit.

Can someone who has the DCX2496 perform the same test please?
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Old 9th February 2007, 02:13 PM   #3
kanguru is offline kanguru  Australia
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Dikke, do you still need someone to do run that test?

If someone has already done it, what were the results?
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Old 9th February 2007, 09:36 PM   #4
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Since there are no replies here, I do not have results.
I shall try to send the low output to my computer and record it as a wave file so you can see and hear the difference.
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Old 10th February 2007, 07:38 AM   #5
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Image:
Click the image to open in full size.

Also 2 files:
No limiting
-4dB limiting
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Old 11th February 2007, 08:24 AM   #6
kanguru is offline kanguru  Australia
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OK, I'll see if I can duplicate your setup and see if I have the same problem. Unfortunately I don't have any UB40; you'll have to suggest something else.

What I have so far: PC -> iTunes (Apple Lossless filetypes) -> Airport Express (avoiding resampling to 48kHz) -> spdif -> DEQ2496 (no other way to get an AES/EBU, but all its processing is switched off) -> AES/EBU -> DCX2496 (in on A, out on 1,2) -> Behringer UB802 mixer -> Senn HD650s

I haven't used my DCX2496 before, but I think I have it set correctly.

What is the release time set to on your OUT1 limiter? I seem to hear unexpected high frequencies with the limiter both on and off, but I suspect the mixer as its peak LEDs are flashing even though inputs are set as low as possible. Behringer would probably say this DCX is even more defective than yours.

My DCX is running version 1.16

I'm happy to do more tests and record the results as a WAV file.

k.
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Old 12th February 2007, 04:12 PM   #7
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Set the DEQ gain offset to -15dB.
This way the output of the DCX is between -20 - -10dB, so you mixer inputs won't clip.
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Old 13th February 2007, 11:28 AM   #8
kanguru is offline kanguru  Australia
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Quote:
Originally posted by Dikke Foaf
Set the DEQ gain offset to -15dB.
This way the output of the DCX is between -20 - -10dB, so you mixer inputs won't clip.
OK, done. I hear what you describe, crackling when the "limit" LED lights.

I'll record the signal and run a spectrum analysis which should visually demonstrate the distortion.
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