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Author Topic: Audio Source Switching Issue  (Read 390 times)

Aaron Dymond

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Audio Source Switching Issue
« on: February 21, 2014, 02:28:44 pm »

I'm a new IT support specialist at a college in Baltimore. The classrooms I am responsible for have AV control panels and switchers made by Extron.

The control panel is the MLC 226 IP DV+ and there is one mounted on each teacher station at the front of the classroom. It manages a number of sources, including a doc cam, laptop, and PC AV inputs. The audio is routed to speakers in the ceiling and the video is routed to a projector.

When PC is selected (as it is the default position since almost all profs want to teach from the computer at the podium) they don't get audio upon login. I find that I have to toggle to another input (like "laptop") and then back to the "PC" input to get audio to play. It happens every time.

There doesn't seem to be any documentation that speaks to this, and I can't find a single setting in Windows 7 that will address the issue either. My guess is that as each person logs out, there is some sort of reset signal sent to the switcher. I'm not even sure if that makes sense.

Please offer any insight that may suggest there is a solution to this problem. I searched for something like this and didn't see anything, so if this is misplaced I apologize.

Thanks in advance!
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Jonathan Kok

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Re: Audio Source Switching Issue
« Reply #1 on: February 21, 2014, 04:48:13 pm »

I'm a new IT support specialist at a college in Baltimore. The classrooms I am responsible for have AV control panels and switchers made by Extron.

The control panel is the MLC 226 IP DV+ and there is one mounted on each teacher station at the front of the classroom. It manages a number of sources, including a doc cam, laptop, and PC AV inputs. The audio is routed to speakers in the ceiling and the video is routed to a projector.

When PC is selected (as it is the default position since almost all profs want to teach from the computer at the podium) they don't get audio upon login. I find that I have to toggle to another input (like "laptop") and then back to the "PC" input to get audio to play. It happens every time.

There doesn't seem to be any documentation that speaks to this, and I can't find a single setting in Windows 7 that will address the issue either. My guess is that as each person logs out, there is some sort of reset signal sent to the switcher. I'm not even sure if that makes sense.

Please offer any insight that may suggest there is a solution to this problem. I searched for something like this and didn't see anything, so if this is misplaced I apologize.

Thanks in advance!
While, theoretically, your IT department may have written custom code for the PC that sends an RS-232 signal to the controller upon log-off, it is highly unlikely. I'd look elsewhere. Have you actually tried this yourself and confirmed it to be an issue?
I'd suspect that the 'Off' function of the controller mutes the audio, and the 'On' function does not un-mute it, leaving it in a muted state until a source is (re-)selected.
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Aaron Dymond

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Re: Audio Source Switching Issue
« Reply #2 on: February 21, 2014, 10:27:10 pm »

While, theoretically, your IT department may have written custom code for the PC that sends an RS-232 signal to the controller upon log-off, it is highly unlikely. I'd look elsewhere. Have you actually tried this yourself and confirmed it to be an issue?
I'd suspect that the 'Off' function of the controller mutes the audio, and the 'On' function does not un-mute it, leaving it in a muted state until a source is (re-)selected.

I have verified the problem myself. If what you're saying about the "off" function of the controller mutes while the "on" fails to un-mute is correct, then this isn't correctable (at least not the way I'm thinking about it). It just is. It does feel strange that re-selecting an input source the only way to un-mute the audio. The biggest problem with this is that the average prof doesn't think like this. He/she doesn't think mute vs. un-mute or select vs. re-select - they think "interrupted" and "broken," and somewhat intuitively so; I don't blame them. I'm going to keep looking for some sort of work-around.

But thanks for your quick response!
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Scott Carneval

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Re: Audio Source Switching Issue
« Reply #3 on: February 22, 2014, 11:51:56 am »

I would try to get ahold of the original system designer or installer.  Surely there is documentation somewhere as to who did the install.  It might be as simple as asking the installer, or they may want you to pay them for a service call.  But I would start there.

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Scott Carneval
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Brad Weber

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Re: Audio Source Switching Issue
« Reply #4 on: February 22, 2014, 12:15:08 pm »

The MLC 226 has only one serial port and it is commonly used for the projector control so unless you are sure there is a communication connection between the PC and the Extron control system then I doubt the two communicate.
 
The MLC 226 IP DV+ is simply a controller, it does not actually switch the audio and video but rather controls another device that provides that functionality, typically something like an Extron MLS 406SA or MLS 506SA or even the projector itself.  You might want to verify if there is a separate AV switcher or if the projector is being used to switch the video and audio sources such as the PC.
 
Is the problem specific to the PC or is it common to all inputs?  For example, if you have a laptop connected and had the laptop input selected does the same thing happen for the laptop?  Just trying to determne if the issue is specific to the PC or might also occur for other sources.
 
If an MLS switcher is used then don't believe there is anything in the default programming that would result in the situation you note, but that does not mean the installer may not have modified the default programming.  I agree that I would certainly try contacting the party who installed the Extron system and ask them about the situation.
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