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Dt Cabinet Simulated Direct Out Questions

dt xlr recording direct out cab sim pod hd pa

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#1 radatats

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Posted 28 January 2014 - 07:47 PM

The XLR out on the DT provides a transformer tapped direct out with cabinet simulation.

 

Here are some questions I have, maybe someone can answer them...

 

- does transformer tapped mean they are pulling the same audio that is going to the speaker including power section distortion just at a much lower level straight from the output transformer?

 

- how is cab sim applied?  Does that signal then go back into the DT for processing to add the cab sim?

 

- if I am already using cab sims with my amp/preamp modeling, why would I want another cab sim applied to the output here?

 

- if it is the same type of cab sim as with the amp/pre, what cab are they using?  what mic are they using?

 

- is it linked to the internal amp models stored or to the one being used from the POD?

 

- can the cab sim be adjusted or changed with an external editor in any way?


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#2 MartinDorr

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Posted 29 January 2014 - 10:24 AM

The XLR out on the DT provides a transformer tapped direct out with cabinet simulation.

 

Here are some questions I have, maybe someone can answer them...

 

- does transformer tapped mean they are pulling the same audio that is going to the speaker including power section distortion just at a much lower level straight from the output transformer?

 

- how is cab sim applied?  Does that signal then go back into the DT for processing to add the cab sim?

 

- if I am already using cab sims with my amp/preamp modeling, why would I want another cab sim applied to the output here?

 

- if it is the same type of cab sim as with the amp/pre, what cab are they using?  what mic are they using?

 

- is it linked to the internal amp models stored or to the one being used from the POD?

 

- can the cab sim be adjusted or changed with an external editor in any way?

I don't think I have solid answers, but I can describe my view of how it may work ... (I have not done any of it)

  1. I don't know what transformer tapped really means, except that it is supposed to emulate power amp tone characteristics on the DT XLR out. I think there is no crisper definition of what it actually does within the DT to achieve this.
  2. Cab sim within the DT is most likely done by the DSP and due to cost of additional AD/DA conversion of a transformer tapped analog signal it will most likely be done before the DA conversion of the signal fed to the power amp section (similar to how reverb in the DT is handled, i,e., before the effect loop out (again to save a DA/AD conversion)). Best case scenario would be if there are 2 DAs after a split of the digital signal path: One going to power amp section and the other going to a DSP cab/mic sim stage before being converted to analog for XLR out. Whether the 'transformer tapping' ends up getting mixed in by the DSP (would required some AD of transformer tapped signal) or in the analog domain is an open question.
  3. Cab / Mic sim is just just a form of EQ / compression combo characterized for a specific Cab/Mic selection. Use it if you like the effect. Even Line 6 seems to have opted for turning Cab sim on in the DT preamp section even though they clearly send the output primarily to the DT speakers. Obviously they could play some more tricks in the DT to compensate for the DT speaker. Would be hard to verify, I think.
  4. Don't know what they did before the latest DT FW update. Now I believe they describe it in the DT MIDI specification, but I did not recheck.
  5. The Cab sim selected in the HD is done by the HD DSP; the cab sim in the DT for the XLR out is done in the DT DSP, I think. They could be aware of each other, but there is no documentation saying so as far as I know.
  6. There are DT MIDI editor SW programs (search forum, i don't recall details) and you can use any generic MIDI control surface/device to control the Cab/Mic setting for the 8 program slots in the DT (once they are programmed the Type sector on the DT is used to select the program (together with the amp type) on channels A and B.

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#3 radatats

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Posted 29 January 2014 - 12:19 PM

thanks but none of those actually answer the questions.  Unfortunately there is no documentation of this feature and there are a lot of issues with the XLR out from the DT.  I appreciate your input though...


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#4 phil_m

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Posted 29 January 2014 - 12:27 PM

- does transformer tapped mean they are pulling the same audio that is going to the speaker including power section distortion just at a much lower level straight from the output transformer?

Essentially, yes. So what it means is that it's not simply the preamp signal with cab emulation. You get the power amp interaction as well.

 

- how is cab sim applied?  Does that signal then go back into the DT for processing to add the cab sim?

 

Yes, the cab emulation is added post this signal.

- if I am already using cab sims with my amp/preamp modeling, why would I want another cab sim applied to the output here?

- if it is the same type of cab sim as with the amp/pre, what cab are they using?  what mic are they using?

- is it linked to the internal amp models stored or to the one being used from the POD?

It's my understanding that if you're connected to the POD via L6Link, the cab simulation will be the same as whatever you have in the preset on the POD.
 

- can the cab sim be adjusted or changed with an external editor in any way?

 

I don't believe so. The DEP control in the POD don't effect this simulation as far as I know.


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#5 radatats

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Posted 29 January 2014 - 02:00 PM

thanks Phil, kind of what I suspected but just not really diggin why they do it this way.  I start with a digital modeled amp and cab, send it through an analog tube amp and then back into the digits to get a second cab makeover and back AGAIN to a usable audio signal to the board...  so I guess the DT knows what cab setting I have in the POD and then uses the same cab/mic config in the DT to process my signal a second time...  Wow...  so what happens if I have no cab selected in the POD? Hmmmm...  Why can't it just go from the transformer tap to the XLR without another digital makeover?


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#6 phil_m

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Posted 29 January 2014 - 02:30 PM

Why can't it just go from the transformer tap to the XLR without another digital makeover?

 

That probably wouldn't sound too great, I imagine. What are you wanting to do with the signal?


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#7 radatats

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Posted 29 January 2014 - 02:33 PM

same as everyone else, run it to the PA... it is such a weak signal though and I can't understand why...


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#8 phil_m

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Posted 29 January 2014 - 04:07 PM

Well the XLR out is mic level, not line level. So you have to take into a preamp and treat it like you'd treat a dynamic mic, more or less.


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#9 Brazzy

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Posted 29 January 2014 - 05:32 PM

From what I'm gathering you can run the XLR out of the DT into the mic of the HD500 thru a clean channel and out the XLR's to PA.
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I mostly play at home and my own music which is more of a bluesy Jazzy Rock mixture as I'm still learning how to play guitar so when I post a reply to try and help give ideas you know where I'm coming from. In a nutshell I'm always learning and having fun doing it. Rock-On!! Oh, and if I don't respond promptly I'm probably playing guitar or my computer locked up from multitasking 'cause I'm using Gear Box, HD500 Edit, Audacity and tab filled browsers all at the same time, Hahahaaaa. Surprisingly enough my 'puter handles the load more times than not.
 

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#10 phil_m

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Posted 29 January 2014 - 06:35 PM

From what I'm gathering you can run the XLR out of the DT into the mic of the HD500 thru a clean channel and out the XLR's to PA.

 

You shouldn't need to resort to that. Just take the XLR out into a channel strip on the mixer. As long as you're going into a strip with a mic pre, it should be fine.


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#11 innovine

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Posted 30 January 2014 - 02:22 AM

Essentially, yes. So what it means is that it's not simply the preamp signal with cab emulation. You get the power amp interaction as well.

Yes, the cab emulation is added post this signal.

 

 

This is NOT what Line6 support says. Below is a conversation I had with Line6Hugo (hmerida) about cab modelling, and LVM. Hope it provides some information on Line6's stance. Bear in mind that I asked basically these questions in a different support ticket, and some of the answers I got there do NOT agree with this info. So I think Line6 themselves have different answers depending on who you ask... Professional, eh?

Anyway:

 

Line6Hugo: When connected via L6 LINK, the cab model in the DT25 is simply being controlled by the HD500 User Interface. Using the default cab models (the ones which automatically pair with the preamp) should provide the same results when using the same preamp and default cab model in the DT25 stand alone.


Me: "In your explanation, the cab modeling is placed before the power amp, not after. Is this really the case, and if so, why is that? It makes much more sense to have it afterwards. Also, why is there cab modeling active in the dt25 standalone when it has a cab and speaker anyway?"

Line6Hugo: - Cab modeling exists in the DT25 to create a complete amp tone. If you prefer to turn it off you may do just that with a connected HD500 or in standalone mode when connected to a MIDI controller accessing the DT25 2.0 firmware features. Having the cab modeling before the power amp in the DT amps ensures a consistent experience when using with or without a POD HD device.


Me: "How does the use of LVM mode and the direct out affect the placement and operation of cab modeling?"

Line6Hugo: - LVM has no impact on the cab modeling. Direct out uses the same cabinet model through a model of the mic’ed DT25 cabinet. This provides a tone which matches the cab model that comes through the DT25 speaker through a mic, as you would here in a recording or through the PA… essentially the same experience you would get with a microphone but direct via XLR.


Me: "Finally, I notice a large difference on the B channel when I activate LVM. My test case is as follows: dt25 a and b channels set with all knobs to 12oclock, topology 2, P-75 Pre (no cab) I have a footswitch set to toggle the amp block on and off and they sound similar (but far from identical). However, if I engage LVM and toggle the amp block on and off, the B channel now sounds very different (much more distorted). Why is this, nothing in your explanation suggests why the power amp/LVM would behave differently."

Line6Hugo: - More information is required to properly answer this question – normally toggling an amp model bypass (on a connected HD500) also toggles the amp between channels A and B. If channel B is not set identically to the amp model when active, the sounds will be different. Also, each channel (if switching) must have its topology settings set identically. Engaging LVM does two things: uses HD Technology to deliver the preamp and power amp modeling (whereas non-LVM provides just the preamp model) as well as scales the level of the Master Volume knob on the DT25.

 
 
 
Some more conversations with support. might be of interest:
 
From 'afisher'
Hello,

With the DT in LVM and using the direct out, disabling the cab modeling on the HD500 will remove the cab modeling from the output of the DT.

Removing the cab modeling causes the mic modeling to be removed as well.

We tested this scenario here and our ears told us there was no perceived change in tone when changing mic models while the cab modeling is disabled. Thus, the mic modeling does nothing when no cab is being modeled.
 
 
 
 

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#12 innovine

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Posted 30 January 2014 - 02:24 AM

I start with a digital modeled amp and cab, send it through an analog tube amp and then back into the digits to get a second cab makeover and back AGAIN to a usable audio signal to the board...  so I guess the DT knows what cab setting I have in the POD and then uses the same cab/mic config in the DT to process my signal a second time

As far as I understand it (not far!), there is no audio going back to the pod. The cab modelling is applied at/after the PREAMP stage only.


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#13 radatats

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Posted 30 January 2014 - 04:19 AM

thanks for all that!  as usual, they really don't know what the hell is going on because they will not release a simple block diagram of the actual signal path.  It is impossible for the cab modeling to be applied before the power section because it is already being applied there!  They are most certainly applying it a second time to the transformer tapped signal or there would be absolutely no need to mention it at all.  The only way that can happen is for that signal to be routed back in to the DT to have the cab modeling applied prior to hitting the XLR out.  From what I gather from all this discussion is the L6 signal tells the DT which cab is being used in the POD and the DT applies that cab model to the signal.

 

Line6Hugo: - LVM has no impact on the cab modeling. Direct out uses the same cabinet model through a model of the mic’ed DT25 cabinet. This provides a tone which matches the cab model that comes through the DT25 speaker through a mic, as you would hear in a recording or through the PA… essentially the same experience you would get with a microphone but direct via XLR.

 

So this kind of makes sense.  I have to picture this XLR out as representing a mic placed in front of my cab/speaker so even though the tone coming from my cab/speaker is being created with a modeled amp and cab sim, the mic would capture a second physical cab effect and that is what they are trying to recreate.


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#14 phil_m

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Posted 30 January 2014 - 04:45 AM

This is NOT what Line6 support says. Below is a conversation I had with Line6Hugo (hmerida) about cab modelling, and LVM. Hope it provides some information on Line6's stance. Bear in mind that I asked basically these questions in a different support ticket, and some of the answers I got there do NOT agree with this info. So I think Line6 themselves have different answers depending on who you ask... Professional, eh?

 

I don't believe I said anything that contradicted what Hugo said there. You asked specifically about LVM. I was answering as if the DT was in regular power mode.


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#15 innovine

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Posted 30 January 2014 - 05:31 AM

I meant that some other line 6 supporter gave contradictory info. Unfortunatel' they seem to have deleted that ticket, I can't find the conversation. My point is that the line 6 support guys give hazy, ill-defined answers because they don't actually know any better imho. I pressed them really hard for a signal chain block diagram, but 'the display on the pod shows the signal' was the best I got from them. Gah!
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#16 innovine

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Posted 30 January 2014 - 05:35 AM

Radatats: line6 were adamant that no audio goes from the dt to the pod. The dt can do the cab modelling. It makes sense to me to do it while the signal is still digital, and not after the power amp, even if thats where it should be done for most realistic effect. Why don't you think its done earlier in the chain?
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#17 radatats

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Posted 30 January 2014 - 06:07 AM

Radatats: line6 were adamant that no audio goes from the dt to the pod. The dt can do the cab modelling. It makes sense to me to do it while the signal is still digital, and not after the power amp, even if thats where it should be done for most realistic effect. Why don't you think its done earlier in the chain?

 

I am not saying anything goes back to the POD from the DT.  But you are missing the point here.  The signal is created in the POD with modeled amp and cab/mic sim applied.  This is then sent to the DT power section.  At the output transformer the main signal is sent to the speaker and another signal is tapped off for the direct out.  That tapped signal is what is routed back in to the DT to have the cab sim applied based on what model is selected in the POD and then sent to the XLR.  It never goes back to the POD.  This signal now imitates the signal that a mic placed in front of your cab would pick up and is available to send to the mixer for your PA. 

 

If it was done earlier in the chain it would not be able to capture the tube power section flavoring.  I guess my biggest gripe was the weak signal but it is what it is...  I can deal with it now I really understand it.


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#18 innovine

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Posted 30 January 2014 - 06:14 AM

What suggusts that cab/mic modelling is applied again? I'm not saying its not, but what makes you think it is?
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#19 radatats

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Posted 30 January 2014 - 06:26 AM

They state that it is! Its a CAB SIMULATED DIRECT OUT!  the cab sim imitates the physical speaker.  two paths out of the transformer, one to a real speaker, the other to a cab sim (speaker replacement)...


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#20 MartinDorr

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Posted 30 January 2014 - 06:41 AM

I am in innovine's camp. Nowhere does it say the Cab sim is applied to the transformer tapped signal directed to the XLR out. It is much more likely (less DA/AD converters are needed) that the Cab sim is happening in the tail end of the preamp model, i.e., in the HD when an Amp is selected and L6 Link is used, or in the DT if you come in with a guitar or via Channel B when no Amp is selected in the HD.
Another indicator why this is likely is that both Master Volume and Reverb are applied BEFORE the DT effects loop, i.e., the analog signal coming back from the effects loop is probably not converted back to the digital domain to do an extra Cab and Mic modeling step. If the extra AD/DAs would exist, it would make a lot more sense that reverb and master volume would also be done after the effects loop.
Obviously we're all just guessing with spotty and conflicting feedback from several sources and probably no real measurement data we acquired ourselves.
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