DCX : How to create an LT? - Is it the right device?

[Drizt]

Hi Guys,

Ive had a bit of a play around with the software and got a bit of a feel for it, but wanted to ask those that actually used the device before if its a good thing to use to create an LT?

Also if you wouldn't mind could you add a run down on what you did..

Cheers.

[Drizt]

Also, what are the negatives of the unit?

Does it cause a thump at turn on?

[Wayne A. Pflughaupt]

What is a LT?

Regards,
Wayne

[Drizt]

Linkwitz Transform -> http://sound.westhost.com/linkwitz-transform.htm

Heres a calculator from this site -> http://www.hometheatershack.com/foru...alculator.html

[Drizt]

Drizt wrote:

Also, what are the negatives of the unit?

I know the unit outputs pro levels, which I believe my Quest 3004 can handle (theres a button for lowering the gain - I think thats all that is required).

And I believe the unit works better with pro levels on the inputs? Is that correct.

The Behringer MX882 is what Im planning to use to Sum the LFE + L & LFE + R and possibly up the inputs to the DCX to pro levels.

Just wanting to be over cautious and ask as many questions as I can before I jump in and possibly buy the wrong combination of kit.

Any thoughts?

[lsiberian]

The DCX can do anything eq wise that can be done so yes it's the right device.

To use it you will need an amp with trims or XLR-RCA with -12db attenuators.

[Drizt]

lsiberian wrote:

The DCX can do anything eq wise that can be done so yes it's the right device.

To use it you will need an amp with trims or XLR-RCA with -12db attenuators.

Thanks for the reply.

I have been looking through the Quest 3004 documentation and have found the following.

There is input trims on the front and there is a gain selector on the back.

amplifier performance
• Amplifier gain
The amplifier should always be operated with the input
level controls set at maximum. The only departure from
this practice is where the internal filters/crossover is
engaged in a bi-amp configuration, where it may be
necessary to turn down the high frequency side of
the amplifier. If the amplifier needs to be calibrated, to
match a mixer line level output, the gain switch on the
back of the amplifier can be switched to the correct
line level.

On the back of the unit the gain setting options are:

7. Selectable Gain Settings
Adjustable input switching for 1.4V, 32 dB or 26 dB make system calibration easy.

What option should I be using given the output of the DCX ? What is the 1.4V setting and how does it compare to the other two options ?

[Drizt]

Can anyone confirm ?

Drizt wrote:

Thanks for the reply.

I have been looking through the Quest 3004 documentation and have found the following.

There is input trims on the front and there is a gain selector on the back.



On the back of the unit the gain setting options are:



What option should I be using given the output of the DCX ? What is the 1.4V setting and how does it compare to the other two options ?

[brucek]

7. Selectable Gain Settings
Adjustable input switching for 1.4V, 32 dB or 26 dB

The 26dB and 32dB settings are fixed gain settings that assume the pro standard input. So, for an input level of 0dBu (=0.775vRMS), the output of the amp will produce a voltage gain of 26dB or 32dB depending on the switch setting.

The 1.4V setting is a sensitivity setting (as opposed to fixed gain) that says the amplifier will produce its full power output (i.e. 1100watts @4ohms) with 1.4volts input. The 1.4v is a broadcast standard where 1.4v=0VU.

The DCX output will be at the standard pro level, so I would choose either 26dB or 32dB. If 32dB peaks your limiters, then drop to 26dB.

The MX822 can also set any level you wish, so I don't see that you have any problems. It's all balanced and all at pro levels.

brucek

[Drizt]

Thank you.

brucek wrote:

The 26dB and 32dB settings are fixed gain settings that assume the pro standard input. So, for an input level of 0dBu (=0.775vRMS), the output of the amp will produce a voltage gain of 26dB or 32dB depending on the switch setting.

The 1.4V setting is a sensitivity setting (as opposed to fixed gain) that says the amplifier will produce its full power output (i.e. 1100watts @4ohms) with 1.4volts input. The 1.4v is a broadcast standard where 1.4v=0VU.

The DCX output will be at the standard pro level, so I would choose either 26dB or 32dB. If 32dB peaks your limiters, then drop to 26dB.

The MX822 can also set any level you wish, so I don't see that you have any problems. It's all balanced and all at pro levels.

brucek

[Drizt]

Found a good post on how to create LT's using the DCX (and other such devices)

http://www.htguide.com/forum/showpos...37&postcount=3

Most of the better digital EQ boxes, e.g. the Behringer DEQ2496 or DCX2496 can do it with ease.

The LT can be replicated as the sum of 3 filters - two band (bell shaped) filters and one 12dB/octave shelving filter. The first band filter changes the Q of the box/driver to 0.7 at it's Fb. The shelving filter changes the response to Q=0.7 at the new desired Fb. The second band filter sets the Q to whatever you want it to be, e.g. Q=0.5, at the new Fb.

In practice, you may not even need the band filters. Just use a shelving filter to boost the lows. If the final response curve looks the way you want it to, it doesn't matter how you get there or what kind of fancy name you give it. It's all just EQing the bass response to be the way you want it.

[Drizt]

I ended up sending an email to Quest to see what setting they recommend, and they said to use the 1.4V setting.

, I wish I knew more than mooo all about electronics :P

brucek wrote:

The 26dB and 32dB settings are fixed gain settings that assume the pro standard input. So, for an input level of 0dBu (=0.775vRMS), the output of the amp will produce a voltage gain of 26dB or 32dB depending on the switch setting.

The 1.4V setting is a sensitivity setting (as opposed to fixed gain) that says the amplifier will produce its full power output (i.e. 1100watts @4ohms) with 1.4volts input. The 1.4v is a broadcast standard where 1.4v=0VU.

The DCX output will be at the standard pro level, so I would choose either 26dB or 32dB. If 32dB peaks your limiters, then drop to 26dB.

The MX822 can also set any level you wish, so I don't see that you have any problems. It's all balanced and all at pro levels.

brucek

[Drizt]

I found a very helpful post that explains the math behind the decision to use the 1.4V setting for gain on the Quest 3004 (in my case).

http://www.controlbooth.com/forums/s...tml#post102969

Lets hope its right

Re: Use of plus 4/minus 10 (+4/-10) switches?
Almost. :-)

I was working through the math of this the other night for a project. +4dBu is a voltage signal, referenced to 0.775 V. Thus, 4 dBu is actually 1.228V. (4 = 20*log(V/0.775); thus 0.2 = log(V/.775) and V = 0.775*(10^0.2))

-10 dBV is also a voltage signal, but referenced to 1V. So this signal would be 316 mV (-10 = 20*log(V/1); thus -0.5 = log(V) and V = 10^-0.5 = 0.316).

Thus, the difference in voltage would be: V = 20*log(1.228/0.316) = 11.79, or approximately 12 dB difference in signal strength.

THe short answer to your question is that almost all consoles reference their outputs to 4dBu, unless noted. Most IEM gear will probably have a switch on it. So just set the switch to +4 dBu and plug it up.
__________________
Mike Benonis
Grad Electrical Engineering '14, Virginia Tech
Electrical Engineering '09, The University of Virginia
KI4RIX
http://www.benonis.net/

[brucek]

explains the math behind the decision to use the 1.4V setting for gain on the Quest 3004 (in my case).

I don't see how this encourages you to use the 1.4 volt setting?

The DCX has a max output pro level of +22dBu = 9.75 VRMS. math = (0.775 antilog (22 / 20).

So if the amp setting of 1.4 says that full power output is reached when 1.4 volts is at the input, what will happen when you feed the amp 9.75 volts (+22 dBu)?

brucek

[Drizt]

To be honest its from piecing all the information together and trying to join the dots together. I admit I know very little about electronics.

I have been told in this thread that DCX would out pro levels and that to bring it down to consumer levels it would need to be attenuated by 12dB. The math above, I thought, showed that by using the 1.4V sensitivity would in effect account for this 12dB difference. It also shows that at pro levels (+4dBu) that the output would be below 1.4V, so never able to achieve full output.

Also I emailed quest about using pro level inputs into the amp and they said to use the 1.4V setting.

The figure of +22dBu you list below is the first I have seen in reference to the DCX. Can you link to this for me please?

brucek wrote:

I don't see how this encourages you to use the 1.4 volt setting?

The DCX has a max output pro level of +22dBu = 9.75 VRMS. math = (0.775 antilog (22 / 20).

So if the amp setting of 1.4 says that full power output is reached when 1.4 volts is at the input, what will happen when you feed the amp 9.75 volts (+22 dBu)?

brucek

[Drizt]

brucek wrote:

The MX822 can also set any level you wish, so I don't see that you have any problems. It's all balanced and all at pro levels.

brucek

Ill be using the MX882 to mix channels on the input side to the DCX. I had a look at feeding the outputs of the DCX back into the MX882 but from what I could see that would end up creating a feedback loop if I used the main outputs which I intend to.

[brucek]

I have been told in this thread that DCX would out pro levels and that to bring it down to consumer levels it would need to be attenuated by 12dB.

No, you will be using all pro levels and all balanced. There is no need to convert to consumer level. No attenuation required.

It also shows that at pro levels (+4dBu) that the output would be below 1.4V, so never able to achieve full output.

No, the +4dBu refers to the nominal pro level, just as -10dBv refers to nominal consumer level. The max levels are listed in the device manuals.

The MX882 spec sheet (download here), and the DCX is the same (download here). Both +22dBu max out.

brucek

[Drizt]

How have you come to that? Im lost.

I will be using the Integra DHC-9.9 which has XLR outputs. But I assume this is a consumer level product and will not output pro levels?

I may also integrate my 2ch rig with the HT rig and would then need to mix single ended (RCA converted to XLR) with the LFE from HT via the MX882.

The DCX works best a pro levels so I could use the MX882 to raise the levels to pro levels.

The quest 3004, i have ****. I had assumed if i feed it the pro levels from the DCX that it would have a fit. And that I would need to compensate for the 'pro' levels.



No wonder people pay extra to just buy consumer level goods that do it all for you. Too much stuff to work out for most people I would imagine.

I must say you have thrown a spanner in the works. Your telling me different information than what the equipement manufacturer is telling me.

brucek wrote:

No, you will be using all pro levels and all balanced. There is no need to convert to consumer level. No attenuation required.


No, the +4dBu refers to the nominal pro level, just as -10dBv refers to nominal consumer level. The max levels are listed in the device manuals.

The MX882 spec sheet (download here), and the DCX is the same (download here). Both +22dBu max out.

brucek

[brucek]

How have you come to that? Im lost.

The MX882 can set any level you want. You want pro.

I had assumed if i feed it the pro levels from the DCX that it would have a fit.

It's a pro level amp. I see no reason for it to have a fit if you send it pro levels. They provide a sensitivity and fixed gain switch along with a GAIN Input switch to calibrate mixer line levels to amplifier input sensitivity.

No wonder people pay extra to just buy consumer level goods that do it all for you. Too much stuff to work out for most people I would imagine.

The pro equipment gives you options.

I must say you have thrown a spanner in the works.

You may be worrying about it too much. If one setting doesn't work, try another.

brucek

[Drizt]

Thanks for your help.

I guess Im just confused as the Quest guys told me to use the 1.4V sensitivity setting.

brucek wrote:

The MX882 can set any level you want. You want pro.


It's a pro level amp. I see no reason for it to have a fit if you send it pro levels. They provide a sensitivity and fixed gain switch along with a GAIN Input switch to calibrate mixer line levels to amplifier input sensitivity.


The pro equipment gives you options.


You may be worrying about it too much. If one setting doesn't work, try another.

brucek

[Drizt]

brucek wrote:

You may be worrying about it too much. If one setting doesn't work, try another.

brucek

If I try a setting which causes the input on the Quest to 'clip' could that damage a subwoofer driver? I know clipping can kill a tweeter pretty quick, but what about a subwoofer?

I found a nice simple PDF to explain the fixed gain and sensitivity settings on amps in case anyone is interested -> http://www.proaudiosystems.co.uk/doc...ntrollers..pdf

I think now I understand what brucek is saying about causing clipping if using the 1.4V setting.

Is this right (I posted this elsewhere to):

Scenario 1 (NO EQ):
If we gave normal pro levels (+4dBu) to the DCX and applied NO eq, then the DCX would output pro levels (+4dBu) which would mean selecting the 1.4V sensitivity gain setting on the Quest 3004. This would mean that +4dBu would be the highest output coming from the DCX (representing 100% signal). Is that right?

Scenario 2 (With EQ):
Lets say I use 6dB gain at 20Hz to extend the bass output of my sealed Maelstrom-X subs. With the same pro levels in, would the DCX now output +10dBu (+4dBu + 6dB gain) as its maximum output for a 100% signal strength for a 20Hz tone ? So if the Quest was set to 1.4v and it recieved a +10dBu signal it would cause clipping ?



So in this case if using the 1.4V sensitivity setting on the Quest, would I need to apply a negative gain (attenuation) of 6dB to the inputs on the Quest to ensure no clipping occurred?



If your using the fixed gain settings, how do you know how much is too much gain?
Eg. Lets say the DCX was outputting +10dBu at 20Hz for a 100% signal strength (I hope I have the terminology right) like in scenario two, that would mean there would be 36dB gain if using the 26dB fixed gain setting or 42dB gain using the 32dB gain setting.

How much gain is to much ?

[brucek]

There isn't much chance in damaging a subwoofer with a clip now and then, but I don't see much chance of that happening to you with that amplifier. It has Peak Status LED's that warn you that you are approaching clipping (not clipping, but approaching clipping). Then you have a switchable Limiter control that prevents the amplifier from clipping or distorting.

You can't look at a music signal as some steady state sine wave that is at exactly +4dBu. The standard reference to +4dBu and -10dbV are nominal readings for pro and consumer. They are not peak - but more of an average. The pro output peak on your devices driving your amplifier are +22dBu. You don't need any EQ to reach those levels, but an EQ filter of +6dB will certainly raise the level by that much at that specific filter frequency. So when you ask, "This would mean that +4dBu would be the highest output coming from the DCX (representing 100% signal). Is that right?, the answer is no. That's a nominal level and any peak in the music can reach +22dBu before clipping the DCX.

You have to pay attention to the gain structure of your entire chain. Too much level and you'll clip, and too low a level and your S/N raises. Most pro equipment have VU's to help you set your levels. Try and set the levels so that each stage receives the maximum signal without clipping when the loudest volume listening level is used from your receiver. Do some reading about audio gain structure on the internet - it's one of the more important subjects in the pro equipment world.

brucek

[Drizt]

Thanks again. That was very helpful.

brucek wrote:

There isn't much chance in damaging a subwoofer with a clip now and then, but I don't see much chance of that happening to you with that amplifier. It has Peak Status LED's that warn you that you are approaching clipping (not clipping, but approaching clipping). Then you have a switchable Limiter control that prevents the amplifier from clipping or distorting.

You can't look at a music signal as some steady state sine wave that is at exactly +4dBu. The standard reference to +4dBu and -10dbV are nominal readings for pro and consumer. They are not peak - but more of an average. The pro output peak on your devices driving your amplifier are +22dBu. You don't need any EQ to reach those levels, but an EQ filter of +6dB will certainly raise the level by that much at that specific filter frequency. So when you ask, "This would mean that +4dBu would be the highest output coming from the DCX (representing 100% signal). Is that right?, the answer is no. That's a nominal level and any peak in the music can reach +22dBu before clipping the DCX.

You have to pay attention to the gain structure of your entire chain. Too much level and you'll clip, and too low a level and your S/N raises. Most pro equipment have VU's to help you set your levels. Try and set the levels so that each stage receives the maximum signal without clipping when the loudest volume listening level is used from your receiver. Do some reading about audio gain structure on the internet - it's one of the more important subjects in the pro equipment world.

brucek

[Drizt]

brucek,

Thanks again for all your help. I know it must be frustrating trying to explain it to me. I appreciate the effort.


I think I can use the one MX882 to lift the level going into the DCX and then drop them back down after the DCX.

It seems that each input can be set to split or mix mode. I originally thought the whole unit was either in split more or mix mode, but seems it can be done on an individual channel basis. I know I know, moo baby moo. :P

So I could do...

Main inputs, are the LPF (40Hz and below) output from my active main speakers.
Input 1 could be the LFE channel which gets mixed into both the L & R main outputs.
Set the main output levels appropriately for the DCX.

This could then be feed into the DCX .
The output from the DCX could then be feed back into the MX882 on channels 3 & 4.
Set those channels to 'split' mode (so that they don't get summed to the main outputs and create a feedback loop).
Set the output levels to what is appropriate for the inputs of the Quest 3004.

Work out the appropriate gain or sensitivity on the Quest.

I 'THINK' thats how it could work.

[Drizt]

brucek wrote:

Try and set the levels so that each stage receives the maximum signal without clipping when the loudest volume listening level is used from your receiver.

My reciever is an Integra DHC-9.9.

Would you use the tone generator in the Intregra that you use to calibrate the system to reference levels (think that 85dB) ? Or whats the appropriate method to send out the loudest volume? Sorry that might be stupid question, but just wanting to double check my procedure.

I assume you can send all these signals through the behringer and quest gear without the subs connected to the amp? Just want the lights for clipping and adjust?

brucek wrote:

Do some reading about audio gain structure on the internet - it's one of the more important subjects in the pro equipment world.

brucek

Will do. Ill look into it tonight. Thanks again.