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Line 17/18 on XR18

Contributor - Level 2
Is it possible to include the option to split these into 2 separate channels with independent routing?
I understand there is limited EQ and no dynamics on these inputs, but for use as a talk-back channel or a mono music playback this would not matter.
If the hardware wont allow this, could someone from Behringer kindly just explain this, and people will understand why it cant be done.
Thank You!!
9 REPLIES 9

17/18 routing as two mono channels?

Contributor - Level 2
This is a old thread but is something I would be interested in knowing too.
Any takers?

Re: Line 17/18 on XR18

Contributor - Level 2
I can definitely see the benefit of this, except that my 17/18 are tied up with a phone/aux input. So the USB sound card that streams my TB and Solo connects to XLR/TRS 16 and the Headphone out.

I wish the XR would stream the Solo bus and a specially-designed Talkback natively, using the audio system on the controlling device.
(solo could broadcast, but how to handle multiple TB's? mix all? designate one and ignore the others?)
Then I wouldn't need the USB card or the open-source streaming software that forces me to run Linux at FOH.
(not that I don't like Linux, it's just that Windows' power management drivers tend to be written by the hardware manufacturers directly and thus work better than the Linux community's reverse-engineered ones)

It would also be wonderful if the 17/18 channel strip (and FX returns) were actually full strips, with gate and compression just like the other 16. There have been several times when I've wanted to compress an "excitement/atmosphere track", keyed from an MC's mic, forming a ducker. But the playback/FX channels don't compress! Smiley Sad


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As for possibility, it's all software. All inputs and outputs are physically independent from each other. The software might be designed to make some things convenient for the developers at the expense of others, so if you want to do one of those others, it becomes a near-complete rewrite, but it's still "just software".

And the sum total has to fit in the chip(s) that run it, which is not always intuitive, especially when you reach that limit and have a few more things to go. (been there!)

Re: Line 17/18 on XR18

Triber Moderator
Bob Mcnair;136042 wrote:
Is it possible to include the option to split these into 2 separate channels with independent routing?
I understand there is limited EQ and no dynamics on these inputs, but for use as a talk-back channel or a mono music playback this would not matter.
If the hardware wont allow this, could someone from Behringer kindly just explain this, and people will understand why it cant be done.
Thank You!!


I'm surprised that myself or someone else here didn't answer this question earlier (probably just got lost in the shuffle) but taking a look at the XR18 block diagram it definitely shows that the line inputs on XR18 are combined before even going through the A/D conversion process. I'll attach a pic below.

For that reason, splitting each channel into separate inputs will not be possible without a significant hardware change. Bottom line, it's best to use AUX in as a stereo pair or use one of the other input channels to bring in mono sources. Smiley Wink
Michael Lapke - Broadcast Storytelling Champion

Re: Line 17/18 on XR18

Contributor - Level 2
Michael Lapke;150653 wrote:
...taking a look at the XR18 block diagram it definitely shows that the line inputs on XR18 are combined before even going through the A/D conversion process. I'll attach a pic below.

For that reason, splitting each channel into separate inputs will not be possible without a significant hardware change. Bottom line, it's best to use AUX in as a stereo pair or use one of the other input channels to bring in mono sources. Smiley Wink


Sure, there's the normalling switch in the Right jack to make the other one Left/Mono (mono feeds both ADC channels through right's switch), but beyond that, it's all software right? (or more accurately, firmware)

(also, I don't see the pic)

Re: Line 17/18 on XR18

Triber Moderator
Aaron Duerksen;150662 wrote:
Sure, there's the normalling switch in the Right jack to make the other one Left/Mono (mono feeds both ADC channels through right's switch), but beyond that, it's all software right? (or more accurately, firmware)

(also, I don't see the pic)


My point was that they can't be split because the signal on LINE IN 17/18 is already combined before the A/D process. That's a hardware limitation and can't be altered by firmware.

Forgot to attach the pic in my last post...
Michael Lapke - Broadcast Storytelling Champion

Re: Line 17/18 on XR18

Contributor - Level 2
Michael Lapke;150700 wrote:
My point was that they can't be split because the signal on LINE IN 17/18 is already combined before the A/D process. That's a hardware limitation and can't be altered by firmware.

Forgot to attach the pic in my last post...


Just because it comes from a stereo ADC doesn't mean that it has to stay a stereo pair in software. You still have two channels. Their gains might be permanently linked in hardware, but from that pic, I don't even see that. Just two copies of some fixed-function conditioning circuitry from the jack to the ADC itself. It's not a mono mix, therefore two separate streams.

Simplified block diagrams like that are really nice to convey the intended use, but can be deceiving in the details. For example, to be a stereo pair at all, there must be two buffers and two lines feeding the ADC, one for each signal, and the ADC itself is in fact two channels in one chip. The reason to show one line is the same as the reason behind a one-line electrical drawing, where most of the "one lines" are actually 3-phase power on at least 3 wires: they all stay together and go the same place, so they might as well be drawn as one, but they are in fact separate wires.

Case in point of a stereo ADC providing separate streams in software is the Alesis HD24 multitrack recorder. It's long been discontinued, but still has an active user base. It uses 12 stereo ADC's and 12 stereo DAC's to record and play back 24 independent mono tracks. It's designed to replace a reel-to-reel tape with a hard drive, so the user interface still bears some similarity to that concept.

Re: Line 17/18 on XR18

Triber Moderator
All I'm able to do at this point is relay the information that's been provided to me from the developers. Any additional clarification would have to be provided by them directly.

What I know is that by design the X AIR AUX IN channel is meant to be a stereo input for bringing in music or any other stereo line level input. It's not meant for bringing in two independant mono sources that require separate processing. That's inherent in the design and the way the control apps function.

So the feature request has been presented here and our developers are able to see it and consider possible future implementation. It's now up to them to determine if it's something that can happen given X AIR's current hardware configuration and processing power.
Michael Lapke - Broadcast Storytelling Champion

Re: Line 17/18 on XR18

Contributor - Level 3
While you can't split the ch 17/18 stereo pair, or apply dynamics to the channel pair, you can use the inputs separately to feed any of channels 1-16.

So, for example, ch 1 can be fed from input 17 and ch 2 from input 18. This obviously uses up 2 regular mic channels, though - and you can't map any other inputs to ch 17/18 - though you might choose to use a USB input pair?

Re: Line 17/18 on XR18

Contributor - Level 2
Alec Spence;150838 wrote:
While you can't split the ch 17/18 stereo pair, or apply dynamics to the channel pair, you can use the inputs separately to feed any of channels 1-16.

So, for example, ch 1 can be fed from input 17 and ch 2 from input 18. This obviously uses up 2 regular mic channels, though - and you can't map any other inputs to ch 17/18 - though you might choose to use a USB input pair?


I didn't think you could do that, so I tried it. Turns out you can! And you can choose to stereo-link the full strips that you've fed from 17/18, or not to stereo-link them and use them completely independently. They don't even have to be next to each other: 17(L) could feed channel 12 and 18(R) could feed channel 7 if you wanted. You just lose the pre-gain altogether when you do that. The AUX channel strip has a digital trim, but you don't even have that anywhere else.

So that's a way to get a full strip's worth of processing on the line inputs, and independent routing, but all of mine are taken up with the band, plus some double-tracking for the double-duty singing/speaking mics. I'm using FX1 as an insert, which leaves its send and return unused, and so I took over the return for my USB jukebox, which keeps the AUX channel available for a phone/laptop on stage. I'd really like the ability to duck both of those, that is, compress them with a key from one of the full strips or maybe the unused FX send. (don't actually send that mix anywhere, just use it as a key source that includes all the speaking channels)

I've seen other people want to compress the AUX with a self-key because their sources aren't exactly predictable. No time to normalize tracks, hot-swapping phones with different volume settings, etc. That's not the best way to do it - live-compressing a finished track instead of normalizing beforehand - but if you do end up in that situation, it can be a big relief.


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So basically, it would be really nice to have all 5 of those stereo strips - AUX and 4 FX returns - become 10 full strips that are stereo-linked by default. And to have all 26 signals fully patchable to all 26 strips. Digital trim should go with the connector just like the XLR preamp does, not with the channel.

Except I also remember hearing something about the DSP being full already. Is *that* true?
This would not be processing any more signals, but it *is* doing more to some of them, and some optimization from being permanently stereo wouldn't be possible. So it does add some to do this, but not as much as it might appear from the user interface changes.
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