Webcast Audio problems

Conversations around originating a webcast for conference, including cameras and mixers.
rmaughan
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Webcast Audio problems

Postby rmaughan » Thu Jul 23, 2009 11:15 am

Our Stake purchased a webcast communicator around March 2009 and we have used it probably 4 or 5 times now for various webcasts. We are currently running the 1.0 version of the firmware.

In general the webcasts go very well except for the audio -- we usually have trouble with the audio being distorted occasionally on the receiving end. This happens no matter how far down you turn the audio level at the reiving locations (i.e. laptop audio or the EJ8/EJ10 boxes) which tells me the source is where the problem is happening.

So my general question is how can we consistently ensure we will have good audio at the input to the webcast communicator. Note that occasional distortion in the video is generally acceptable to people, but when they can't hear or it's hard to understand what is being said, it gets real annoying very fast and they start tuning out.

Below are the details on our webcast setup:

At the Stake Center we have a separate AV closet where the satellite receiver is located and there is an AV panel (see attached picture) in the closet that has multiple knobs that can be turned to select various audio and video options (i.e. satellite, local video, chapel or cultural hall audio, etc.). In this closet I also have a Phillips DVD Recorder (w/160GB hard drive) DVDR3455 and the webcast communicator. Here is how everything is connected:

Webcast Video: The video source (satellite or chapel video) is selected on the AV panel and the RCA video output of the panel is connected to the input of the DVD Recorder. The S-video output of the DVD recorder is connected to the S-video input of the webcast communicator.

Webcast Audio: An RCA stereo audio patch cable (with a mono to stereo cable) is plugged into the RCA output of the AV panel for the desired source (satellite, chapel, cultural hall). The other end of the RCA audio patch cable is plugged into RCA audio stereo input on the DVD recorder. An RCA to 3.5mm mini plug cable is connected from the RCA audio output of the DVD recorder to the "line in" input of the webcast communicator.

The DVD recorder is turned on during the webcast, but actual recording of the audio and video to the internal 160GB hard drive is only done when it is necessary to re-watch the event under the direction and permission of the Stake President. There is no audio level adjustments that can be made from the DVD recorder.

In the chapel, there is a chapel sound system on/off switch and volume control knob and also a satellite sound combination on/off/volume knob. The chapel volume is usually set around a 2/3 and 3/4 level to provide good sound in the chapel and cultural hall areas.

On our first webcast the audio was very distorted and then I found that I could set the "audio input level" on the main menu of the webcast communicator. Since then we have set the audio input level really low (i.e. one or two bars) on the webcast communicator .

We have found with this set up that when speakers at the pulpit talk loudly or more closely to the microphone that the audio comes out distorted at the receive locations of the webcast. Note that the audio doesn't sound distorted in the chapel (i.e. it may be distorting, but it's not perceptible). I have also hooked the video/audio outputs of the DVD recorder to a local TV and have been able to hear the distortion on the TV.

So my question is how do I figure out what position to set volume control know for the chapel audio to provide enough volume for the chapel and cultural hall sound system, but not too much to cause distortion to the webcast box?

I think that I'm going to have to build some kind of a audio level adjustment circuit (i.e. resistor pot) that sits between the audio output of the AV panel in the closet and the input to the DVD recorder.

Feel free to ask for further details or questions.

Thanks!

Rob
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russellhltn
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Postby russellhltn » Thu Jul 23, 2009 11:33 am

robm wrote:I think that I'm going to have to build some kind of a audio level adjustment circuit (i.e. resistor pot) that sits between the audio output of the AV panel in the closet and the input to the DVD recorder.


See my post here
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rmrichesjr
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Postby rmrichesjr » Thu Jul 23, 2009 1:41 pm

robm wrote:...
So my question is how do I figure out what position to set volume control know for the chapel audio to provide enough volume for the chapel and cultural hall sound system, but not too much to cause distortion to the webcast box?

I think that I'm going to have to build some kind of a audio level adjustment circuit (i.e. resistor pot) that sits between the audio output of the AV panel in the closet and the input to the DVD recorder.

...


RussellHltn wrote:See my post here


If RussellHltn's resistor attenuator network isn't exactly right for your particular system, you could use a 5k audio taper potentiometer with the high end on the input, low end on the shared ground, and wiper on the output. A linear taper pot would work, but audio taper would be a little better if you need a lot of attenuation. If you don't have test equipment, adjust the potentiometer by ear for best results.

If you want to do more precise measurement of the levels and distortion, you could use a signal generator and oscilloscope to prove or disprove clipping distortion caused by overload. A sine wave would work, but triangle wave would be better. You could inject the signal through the crab box and a microphone input, or a line input if you have one. To set the level to match a normal meeting, find an output that is not downstream from a point where you have observed distortion, and use the oscilloscope or a tape deck's level meters. Then, use the oscilloscope to check for clipping at each level you have an analog signal, including the output of the receiving unit. After the digital conversion, the compression algorithm may visually distort a triangle waveform without causing audible distortion. However, any clipping ought to be discernible.

russellhltn
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Postby russellhltn » Thu Jul 23, 2009 2:42 pm

rmrichesjr wrote:If RussellHltn's resistor attenuator network isn't exactly right for your particular system, you could use a 5k audio taper potentiometer with the high end on the input, low end on the shared ground, and wiper on the output.


That would work, but it becomes an additional adjustment that needs to be fiddled with and could possibly be mis-set. So from a philosophical standpoint, I prefer a fixed attenuator that matches the 0VU values for the two systems.
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michaelfish
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Audio Solution - Passive Direct Box

Postby michaelfish » Sun Aug 02, 2009 10:10 pm

We just use a Passive Direct Box ($18.99) to balance/adjust audio signals. The Nady DB-1 has two 1/4" inputs (PL55) and a balanced XLR output and allows input attenuation of 0dB, -20dB and -40dB.

The box is also great for running any headphone or line level (such as a laptop, Ipod) into the building's microphone jacks for easy audio patching.

We've never had sucess with the crabs - too much attenuation.

Twenty bucks was worth the time saved in locating parts and soldering an adapter together.

Let me know if you'd like me to send one to you.

michaelfish
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Postby michaelfish » Sun Aug 02, 2009 10:37 pm

robm wrote:Webcast Audio: An RCA stereo audio patch cable (with a mono to stereo cable) is plugged into the RCA output of the AV panel for the desired source (satellite, chapel, cultural hall). The other end of the RCA audio patch cable is plugged into RCA audio stereo input on the DVD recorder. An RCA to 3.5mm mini plug cable is connected from the RCA audio output of the DVD recorder to the "line in" input of the webcast communicator.


Did you plug the 3.5mm jack into the Red or Blue jack on the back of the communicator (red is for mic input, blue is for line audio)?

You didn't say if the DVD recorder audio is distorted. If the DVD recorder AND communicator audio is distorted, you would need to attenuate before the DVD recorder.

If the DVD recorder audio is fine and the communicator audio is distorted, you may have plugged the audio output of the DVD recorder into the MIC jack on the communictor. The line level of the DVD recorder should be matched for the Blue Line input jack on the communicator. If the audio is still distorting on the communicator but not on the DVD recorder, attenuate after the DVD recorder and before the communicator.

Hope this helps.


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