Behringer DCX2496

[MarkZ]

Method

An unmodified Behringer DCX2496 was tested using Rightmark Audio Analyzer (http://audio.rightmark.org/products/rmaa.shtml). The recording device was an M-Audio Transit in loopback mode, set to 24-bit/48kHz sampling rate. The digital optical output of the Transit delivered the signal to a Behringer Ultramatch SRC2000 to convert the optical input to an AES/EBU XLR connection, which in turn delivered the digital signal to the Behringer DCX2496. Two channels of the DCX2496 (all processing options turned off) were then tested with the analog input of the Transit at -1 dB.

Baseline. First, a baseline was recorded (labeled "analog") using the analog output of the M-Audio Transit connected directly to the analog input -- a simple loopback test to determine the capabilities of the Transit. It's been found in a previous test (http://mdz.no-ip.org/audio/benchtest/source/playbackrecord.html) that the measurements were subtly changed by changing the balance between record level and playback level; specifically, noise, dynamic range, and crosstalk performance improved by a few dB when the playback level was at the maximum and the record level low, but distortion remained largely unchanged. Therefore, playback levels were set high and recording levels were set low and remained constant throughout all the tests. The analog loopback data is shown below; note that there's a slight deviation (underperformance) in this test in comparison to the other, probably because of the difference in sampling rate. As expected, the simple loopback test yielded the best performance. This performance was similar to other tests (http://learjeff.com/RMAA/results.html) using the same software.

Behringer DCX2496 performance. Next, the DCX2496 was tested at the same software playback/record level settings. The frequency response showed virtually no degradation in performance until about 10kHz, where there was a very slight (and steady) drop in level. Particularly noteworthy is the effect of the specialized anti-aliasing filter in the SRC2000 which resulted in a dramatic dropoff in frequency response at precisely 20kHz. Distortion performance was degraded slightly with the DCX2496, but remained surprisingly low. The biggest differences come with the noise, dynamic range, and crosstalk performance, perhaps due to the obvious requirement of a separate power supply for the Behringer devices, providing another opportunity for noise to enter the signal path and crosstalk to occur due to its naturally imperfect PSRR.

Inverter test. The next series tested the performance of the Behringer DCX2496 when powered by a low-cost inverter. The inverter, a 160w Jensen JP20, was powered off a 12v source -- the same source that powered the computer that provided the source tones. In addition, the playback level was decreased in this test (columns 3 and 4), accounting for the slight decrease in performance in comparison with the first test (column 2), consistent with previous data. Indeed, the inverter generated a substantial level of noise. The artifacts were particularly strong in the distortion tests, evident in the graphs provided, due to the nature of the signals used for those tests. However, the noise was still reasonably low (roughly -80 dB) and undetectable by ear. It's expected that an improvement may be achieved with a pure sine inverter. It's also possible that RF radiation or noise in the power source contributed to the degraded noise performance. However, it's been reported that the noise performance can be quite poor when using an inverter when the analog input of the DCX2496 is used, so its use is probably application dependent.

Shortcomings of the test. I was unable to verify the measurements on the oscilloscope, since I'm not equipped to make measurements on the order of microvolts. In addition, the paradigm relied on the assumption that the quality of the digital output of the M-Audio Transit was roughly equivalent to the analog output.


Summary

http://mdz.no-ip.org/audio/benchtest/source/behringer/summary.jpg

Frequency Response

http://mdz.no-ip.org/audio/benchtest/source/behringer/fr.png

Noise Level

http://mdz.no-ip.org/audio/benchtest/source/behringer/ns.png

Dynamic Range

http://mdz.no-ip.org/audio/benchtest/source/behringer/dr.png

THD+Noise

http://mdz.no-ip.org/audio/benchtest/source/behringer/thd.png

Intermodulation Distortion

http://mdz.no-ip.org/audio/benchtest/source/behringer/imd.png

Stereo Crosstalk

http://mdz.no-ip.org/audio/benchtest/source/behringer/ct.png

[Derek]

kickass.....great post :)

[tf1216]

Mod the analog output of your DCX2496 then compare your results. I think you may be surprised : )

[MarkZ]

Mod the analog output of your DCX2496 then compare your results. I think you may be surprised : )

What mod are you talking about in particular?

[tf1216]

If you can read french you can go there and browse the menu on the
left : http://thierry-martin.9online.fr/tweakdcx/cadre


Or if you just need the pictures you can go here
http://thierry-martin.9online.fr/tweakdcx/tweakanalog2.htm

I am a member on the Yahoo DCX2496 Group. Some knowledgable guys over there.

Sorry it took so long to reply!

[MarkZ]

Yikes. It's all greek to me. Err...french.

So what's this mod anyway? Or, more appropriately, what part of the circuit shown is already in the DCX2496?

My warranty is ending in a few months I think, so I may be interested in playing around with it.

[npdang]

Glad to see these results. Contrary to popular opinion, it looks like a cheap power inverter doesn't contribute anything audible to the performance of the dxc2496.

[MarkZ]

Glad to see these results. Contrary to popular opinion, it looks like a cheap power inverter doesn't contribute anything audible to the performance of the dxc2496.

At least not when the digital input is used. It remains to be seen how things shake out with the analog source. Unfortunately, my BNCs were the wrong gender, so I didn't have the opportunity to run those tests.

[tf1216]

Click on the second link in my post above. Scroll to the schematic and notice the two colors, one being black, and one being red.

The black is the analog output stage of the DCX2496 and the red is the mod. A friend and I were able to avoid the DCX2496's output stage with 6 fully-balanced analog outputs. The drawing is showing an unbalanced output. It was a tough squeeze fitting all of the capacitors under the cover and I have yet to do more than test the DCX2496 yet but the results are supposed to be very positive.

[MarkZ]

Click on the second link in my post above. Scroll to the schematic and notice the two colors, one being black, and one being red.

The black is the analog output stage of the DCX2496 and the red is the mod. A friend and I were able to avoid the DCX2496's output stage with 6 fully-balanced analog outputs. The drawing is showing an unbalanced output. It was a tough squeeze fitting all of the capacitors under the cover and I have yet to do more than test the DCX2496 yet but the results are supposed to be very positive.

So then you're bypassing the balanced output? That's not something I was really interested in doing. Especially in the car. The test results might prove to be slightly better by doing so (since I did not use a balanced input on the test), but it wouldn't be an appropriate test if I'm going to use that portion of the circuit anyway.

[Diru]

Well fine , this does have some nice features(was looking at the 3200). How does it perform, looks quiet by the spec. Lets have some feedback.

[MarkZ]

Well fine , this does have some nice features(was looking at the 3200). How does it perform, looks quiet by the spec. Lets have some feedback.

It's difficult to directly compare this source (M-Audio Transit + Behringer) with the head units and processors I've used previously, since the entire speaker system is different. However, I'll say this: much to my surprise, the noise performance is what I'd call flawless, even with the inverter. Noise often plagues car audio, mostly due to issues of grounding and installation, but there's always the occasional processor or amp or something that gives you such a hard time that you need to call in a witch doctor. But I've got no audible noise with the car on or off.

I've tuned it by ear with good results. I'm still working out the kinks in my midbass response, as the Dayton RS180 pair isn't quite cutting it for me in terms of overall output capabilities. I've got four Peerless XLS 8" which should do the trick. When my MobilePre USB arrives next week, I'll be able to RTA. I haven't bothered to try the auto-align feature yet to auto set the time alignment, and I probably won't. I may just do direct measurements and manually set it based on those.

I'll post again after I've installed the Peerless drivers and I've got the final tuning set. Since I'm running a FOUR-way up front, the Behringer setup will also allow me to directly compare the same setup as a three-way (by disabling the Morel dome mids and changing the xover points accordingly). Since the Behringer allows you to save presets, I can tune both versions and A/B them. :D

[Diru]

Good to hear, you keep this up and I might go to this X-over.

Oh , I have an idea for a noise canceling bridge for those power inverters. Still working on the design. It so simple and cheap it will make you think how could it work. Keep an eye out for it.

[MarkZ]

It's just hard to tell how the noise is entering the signal path. Induction or through the Vdc outputs?

[Diru]

The noise I am addressing comes from the affordable power inverts (12vdc-120vac). The output of these things are less then useable for audio imho. Most of the affordable ones output a modified sinewave ( or better still a stepped square wave) at about or around 60hz. Then there is the harmonics(120hz,240hz,480hz so on) that get out of them from poor filtering networks.

A quik test to see if a power inverter is suspect, plug your AC(X-over and what not) device into a wall outlet(with the proper ground if used). If there is a change in noise then it may very well be the inverter singing on the AC output.

But as you said, you have no noise car on or off. This is a cool thing to have happen. I commend you on a great wiring job.

I'm sure you and many others that like myself are looking for the last degree of performance out of our systems. Being a DIY, I'm not about to spend hundreds on a true sinewave inverter to run one small device.

So one day I was hanging a picture in my bathroom and I slipped and hit my head on the toilet. Then I came up with this........

(drawing coming soon)

[MarkZ]

The noise I am addressing comes from the affordable power inverts (12vdc-120vac). The output of these things are less then useable for audio imho. Most of the affordable ones output a modified sinewave ( or better still a stepped square wave) at about or around 60hz. Then there is the harmonics(120hz,240hz,480hz so on) that get out of them from poor filtering networks.

Maybe what I should do next is try the test with both a sine and modified sine inverter (if someone wants to temporarily donate a sine). Perhaps also I should put the Vdc's all on the scope to see how much ripple is making its way in. You may be on to something with a power supply improvement rather than a full blown DC replacement, which is popular these days. Then you'd at least retain the ability to use the unit in the house.

But the question still remains: what is the offending component? And is the mechanism induction or improper filtering?

[Diru]

Give or take a few parts and testing this is main idea. This is as simple as it gets. I do have other ideas that are a bit more complex. One useing a old car stereo amp for its power supply and the second uses batteries. Both will use + and - voltage regulators.