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Audio issues IOHD

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Jeff Mack
Audio issues IOHD
on Feb 28, 2009 at 5:57:20 pm

First, MBP, 10.4.11, IOHD up to date firmware and software.

Last night I took part in a live web broadcast for a radio show. HDSDI 1080 60i and stereo XLR into 1 & 2, Downconvert in control panel to 525i and analog audio was selected. Feed then went to a flash site for live viewing (http://www.stickam.com) The video feed worked perfectly but the audio was terribly garbled. To fix it, I had to take the XLR's to mini stereo and input to built in input on the MBP. Then it worked great. The website had a flash encoder built in and it recognized the IOHD video and also audio. I had to switch the audio to built in audio and it worked.

My question is why did the audio not pass through correctly? In the control panel, I noticed the setup tab. Don't know how to change the settings there and I am not on my MBP now so ican't read the choices. I do remember something like dbu settings and framerate choices.

Lastly, I could have sent the audio into my camera. I am using a Z-1 with a miranda AD converter that takes precompression HDV and converts it to 1920x1080 HDSDI. There is also an audio cable that can take the camera audio and embed it into the HDSDI cable. I should have done that but I got to the venue late and didn't have the time to do this. I presume I would have just selected embedded 1-8 right? It almost sounded like a looping delay. I know there were some audio and video delay sliders. These were both set to zero in my original setup.

Jeff


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Bob Zelin
Re: Audio issues IOHD
on Mar 1, 2009 at 6:01:20 pm

you can't feed an analog +4dBu signal (the XLR output of the AJA) in to http://www.stickam.com which has a stereo mini audio input (which is probably expecting a signal lower than -10dBu). You need to ATTENUATE this signal. The garbaled signal is called distortion.

The cheapest way to do this is with any cheapo audio mixer, like a Behringer, which you can get for less than $100.

You will never ever get away from using an audio mixer in our industry - no matter what product you purchase.

Bob Zelin




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Jeff Mack
Re: Audio issues IOHD
on Mar 1, 2009 at 7:57:41 pm

Thanks Bob. I have a couple AJA ADA4's. They have dip switches to go from +4 to -10. You think putting two of those before the IOHD would've worked? So I guess my MBP could take an xlr to mini and attenuate it internally? Cause that's how we got the webcast done - 1080i60 to 535 down convert for the video and then 2 XLR's to a mini split stereo into built in input.

One other thing I may have done wrong. I was in low light and I thought I was adjusting the gain but I accidently went from 60 frames to 30 and then to 15. When I noticed it, I went back to 60 and adjusted the gain. It might have been coincidence that is when we switched the audio. Could it have been a frame rate distortion? Also, next time I intend to send the mic feeds to the camera and then send the audio down the sdi. Will that give me the same problems?

Jeff



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