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Author Topic: How to get rid of an audio hum Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 08-29-2011 10:38 PM                     i just see a lot of grounds going around in a lot of circles ... "ground looping" - I'm getting to blame the mixer ... I bet those RCA inputs on that mixer have a common ground going across the entire jack strip instead of being separated per each input/output switch. Usually "A/B" switching devices (like this mixer for example) with RCA (unbalanced input) jacks, painfully call for ground loop isolators on the input side since the grounds are all tied together as a common and the switches are only on the plus side and no switchable ground-leaving ground all connected together Home A/V units with multiple RCA audio/video inputs usually have a built-in ground isolation inside to eliminate this "hum syndrome"  |  IP: Logged Frank Cox Film God Posts: 2234 From: Melville Saskatchewan Canada Registered: Apr 2011 posted 08-29-2011 11:24 PM                        If we're going to blame the mixer, then why is it that unplugging the tuner and connecting a CD player to the mixer instead (using the same cable) has no hum? Unless I'm missing something (which wouldn't surprise me) doesn't that eliminate the mixer and everything past it (connection to the computer, etc.) as the source of the problem?  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 08-30-2011 11:07 AM                        Frank: your tuner adds the antenna ground. Perhaps a direct box (with isolation) after the tuner then onward would work. Louis  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 08-30-2011 05:19 PM                     Is the CD player a portable (battery opperated)? Even if it is an AC opperated unit, the internal wireing could be different. In some equipment there is a resistor or cap. from one side of the AC input to ground. This could be the difference. (As I said before) unplug the AC to the tuner, then dissconnect the antenna (or try it the other way around), see of the hum goes away. Try turning the AC plug around. Are the 1/4" connectors on te mixer "balanced"? If you are using 2 crt. 1/4" connectors, you are shorting the output of an IC to ground - not good. Ground loops are funky things. Sometimes the strangest things will sol ground loops. FIND A WAY TO USE THE LINE IN ON THE COMPUTER.  |  IP: Logged Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 08-31-2011 10:16 PM                        I have a question... Why can't you move the server to the studio and take a program signal right out of the board or Distribution Amp? I don't see how grabbing the signal off the air is going to do anything to help you here.  |  IP: Logged Frank Cox Film God Posts: 2234 From: Melville Saskatchewan Canada Registered: Apr 2011 posted 08-31-2011 11:35 PM                        Because the studio is located on an Indian Reserve where the only available Internet service is a terrestrial wireless service that's (a) very expensive, and (b) very poor. We run the server here (about 40-some miles away) because it's the nearest point that has a reliable wired Internet service available. Plus I'm here to look after it. I did look into transmitting the signal from the reserve to here by modem over a leased line, but the cost of that was prohibitive and the station would lose one of their incoming phone lines unless we paid a fortune for a new line to be run. We also considered microwave transmission, since the studio already sends the programming up the hill to the tower by microwave link and the idea was to swap the microwave receiver for a repeater, drive the FM transmitter from the repeater and move the microwave receiver here to drive the streaming server. Ultimately, we decided that since we can get an adequate signal most of the time using a high-gain directional FM antenna on a tower here, that's what we use and we'll live with the odd time that we lose the signal due to weather or whatever. Microwave was going to cost significantly more, the FM transmitter is obviously already running and a high-gain "professional" antenna wasn't terribly expensive. We also gave some consideration to the idea of doing a "sneaker-net" system and simply streaming a week's worth of Moccasin Road (the major "original" daily CHXL program) by bringing each week's programming here on a portable hard drive or something so we could just play it locally. But we discovered that re-shaping the transmitter's footprint a bit and using this antenna here give us adequate reception for live streaming and of course that's what we really wanted.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 09-01-2011 05:39 PM                        Your setup seems to be doing what you need and doing it well. Stick with it; finding and eliminating the hum is easier than reinventing your system's wheel.  |  IP: Logged Frank Cox Film God Posts: 2234 From: Melville Saskatchewan Canada Registered: Apr 2011 posted 09-14-2011 01:11 AM                        I updated the CreekFM streaming audio server's operating system to the just-released Centos 5.7 (from version 5.6) earlier tonight and lost my input signal. The tuner was playing but the stream encoder didn't see any input. I discovered that the (software) level settings had changed, so playing around with alsamixer got it going again. And now the hum is gone. The current level settings aren't much (if any) different than the settings I was using before the software update. I don't see anything in the system log that looks directly related to the sound driver included in the Centos update, either. Needless to say, I'm pretty happy about this though I haven't a clue what the Centos update fixed in that regard. You are all invited to tune into the now hum-free CreekFM audio stream if you wish. It's a truly unique radio station, broadcasting from the heart of the Okanese First Nation Reserve in Saskatchewan, Canada. CHXL www.creekfm.com Fifty Thousand Watts of Pow Wow Power! Serving the File Hills First Nations. And the World.  |  IP: Logged

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