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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

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Old 18th January 2010, 02:20 PM   #2391
SQLGuy is offline SQLGuy  United States
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Originally Posted by panomaniac View Post
Hey DT we won't tell the tube fans you're here.

The DCX can do almost all of what the DEQ does - and more. Tho I'd rather do room EQ with the DEQ - it's just easier and more powerful. I do think that the DCX will be fine for your open baffle rig, it worked for me on several I built.

I use a DEQ in front of the DCX for a bit of room EQ and also just for the pretty RTA graphics. I found that the better and better I got at using the DCX and building crossovers, the less I needed the DEQ. But it was a wonderful tool for getting there.

Bottom line, they can work well together. Just come digital (AES - balanced) out of the DEQ into the DCX. Easy.
I'd say that's a bit misleading. They do different things. The DCX is very limited in EQ functions, and, of course the DEQ has no crossover capability. Both can do level adjustments. Both do A/D -> processing -> D/A. Both use AKM DACs and ADCs and SHARC DSP's.... though the DEQ has two SHARC's to the DCX's one. As mentioned elsewhere in this post, the DCX does not do frequency response measurements, while the DEQ does.

I'm running the same setup that Pano mentions, with the DEQ sending AES digital to the DCX. I'm running analog into the DEQ, and I've used the Behringer mic for reading and correcting room/system response.

I had tried to make most of the corrections using just the single per-band pararmetric EQ that the DCX provided, along with various crossover slope and center combinations, but was not able to achieve anywhere near the eveness of a correction result that I got much more easily with the DEQ. If your equalization is simpler than mine, though, you may find that you can tweak a smooth response out of the system by adjusting the DCX with the DEQ set flat and used only for measurement. You could then pull the DEQ out entirely.

Let us know what you find.

P.S. To be clear, the big difference in EQ between the two is the the DCX offers a single parametric EQ for each output, whereas the DEQ offers the choice of a 31 band graphic equalizer per channel, or multiple parametric EQ's per channel, or a setup that provides graphic EQ with the ability to change Q and center frequency on each band (a paragraphic EQ).

Cheers,
Paul

Last edited by SQLGuy; 18th January 2010 at 02:24 PM. Reason: typo and added info
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Old 18th January 2010, 02:37 PM   #2392
mige0 is offline mige0  Austria
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This is just a loop back on your soundcard, right?
Yes, exactly

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Where was this attenuation done? In Arta or somewhere else?
Attenuation was done in ARTA - so the DAC was working at -3dB / -13dB - and so did all the following stages.


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Right. That is why I tried to keep the digital level always at -6dB and used the analog volume control (pot) on my soundcard for level adjustments.

In your case - having used a volume pot of the soundcard is already bad - you have at least altered the signal level of the (buffer / line driver) stages after the volume pot - meaning those (buffer / line driver) stages might have delivered different performance at different signal levels (as shown to be the case with my measurements) and possibly *this* is what you might have measured ?


Michael

Last edited by mige0; 18th January 2010 at 02:44 PM.
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Old 18th January 2010, 03:01 PM   #2393
pidigi is offline pidigi  Italy
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Default measurements

Hi,

sorry for this semi off-topic question, which soundcard do you guys suggest for the transformers measurements? And for the DCX output distortion measurements?

Thanks,

Ciao

Paolo
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Old 18th January 2010, 03:20 PM   #2394
mige0 is offline mige0  Austria
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24 bit, symmetric IN and symmetric OUT - external is my favorite - but seems there are more and more internals that are stunning.
There are a lot available nowadays - actually it might be even hard to find 16bit anyway

Check out good driver support and compatibility with ARTA or whatever you use!

Would have recommended the Terratec Phase 24FW as this one is now for around EUR 100.- but have heard that there can be compatibility problems on the fire wire hardware level.

I use Mackie Onyx 400f but this one is outdated (and was at the expensive side anyway)

Michael

Last edited by mige0; 18th January 2010 at 03:35 PM.
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Old 18th January 2010, 03:50 PM   #2395
mige0 is offline mige0  Austria
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If you are after acoustical measurements as well, the soundcard best should have an adjustable (knob !) MIC input with XLR and phantom power
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Old 18th January 2010, 03:51 PM   #2396
Legis is offline Legis  Finland
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Does anybody know how to reduce the gain in DCX? Can it be done by changing some resistors to smaller, and if so, which ones?
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Old 18th January 2010, 04:02 PM   #2397
Pano is offline Pano  United States
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Quote:
Originally Posted by mige0 View Post
In your case - having used a volume pot of the soundcard is already bad - you have at least altered the signal level of the (buffer / line driver) stages after the volume pot - meaning those (buffer / line driver) stages might have delivered different performance at different signal levels
That's true, and a good point. However I did do soundcard loop measurements at both attenuations and didn't notice any big difference. I was very worried about the levels affecting the measurements.

It is certainly worth another check to see - thanks for pointing it out!

I do wonder if we should take this to a different thread, so as not to clutter up this one. A thread about using consumer soundcards and software for measurements and how to achieve the best results.
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Old 18th January 2010, 04:20 PM   #2398
mige0 is offline mige0  Austria
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Does anybody know how to reduce the gain in DCX? Can it be done by changing some resistors to smaller, and if so, which ones?
Add a resistor of your liking in parallel to the mute transistor

possibly not scientifically the best way but very easy - and easy to remove too


Michael
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Old 18th January 2010, 07:25 PM   #2399
SQLGuy is offline SQLGuy  United States
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Add a resistor of your liking in parallel to the mute transistor

possibly not scientifically the best way but very easy - and easy to remove too


Michael
It would have to be a pretty small resistor, though... 500 Ohms for 3dB of attenuation, 250 Ohms for 6dB, etc.

You could also play around with the values of the 499 Ohm input and 2.32K Ohm feedback resistors in the next stage after mute, in order to reduce gain of that stage. Stock gain is about 4.6X in this stage... well -4.6X, since it's an inverting stage.

Reducing the 2.32K would reduce the gain.
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Old 18th January 2010, 07:31 PM   #2400
Pano is offline Pano  United States
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Or look up a it earlier in the thread for ideas about taking the signal after the first opamp - if you want unbalanced. The feedback resistor could be changed to lower gain, too.
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