Track Down That Studio Whine
     

Alan Peterson, production director at the Radio America Network in Arlington, Va., was puzzled by an unusually strong whine that kept showing up in voiceovers and short-feature recordings made in one of the network’s production studios. The whine was, for the most part, inaudible, revealed only when his editing software was switched to Spectral Mode.

Fig. 1: The 15.6 kHz 'mystery whine' in Al Peterson's production studio. You could hang a picture on that straight line.

In that mode, it would show up as a strong band just a little under 16 kHz; see Fig. 1.

At that frequency it would have been brick-walled before heading up to the satellite. Still, it was a stray signal that should not have been there. It was present only when a mic was open.

Alan swept the room with a precision flat-response Earthworks microphone. He pointed it into every duct, device, rack and cabinet in an effort to find this mystery whistle that no one could hear.

When he pointed the mic towards an older CRT-type TV set in the studio, running 24/7 to capture news audio, his levels went off the scale. Turns out that the horizontal oscillator, operating right around 15.6 kHz, is the culprit. When the TV was turned off, the whine disappeared.

“This was a sound all of us could hear as kids,” Alan says. “Now, as adults, most of us don’t hear it anymore, so it gets ignored. Flat-screen TV users have likely never heard it.”

He notes that many radio newsrooms around the country have TVs on in the background. If these are CRT units, the same condition could happen.

If audio purity is your goal — and until flat-screen units replace all your obsoleted tube sets — check that the horizontal oscillator isn’t adding noise to your studio.

You know, there was a day when stations were required to conduct an Annual Equipment Performance Test that would “proof” out the audio air chain.

Such a test undoubtedly would miss the cause of Alan’s problem; with a proof, the audio oscillator is fed directly into the console microphone input, thereby bypassing the mic and any noises generated in the studio. But for engineers who performed these annual tests, hum, noises and distortion were pretty obvious and could be corrected.

No one seems to have the spare time to conduct a proof nowadays, unless there’s some glaring problem with the audio. Nonetheless, spending even a half hour monitoring the off-air signal with a good pair of headphones can provide some level of confidence as to the quality of your signal. The time should give you a chance to listen to all the elements of the station: music, voice and stop sets.

* * *

It seems that storms have plagued pretty much every corner of the continental United States the last few months.

Engineer Chris Adams snapped (pardon the pun) the pictures seen in Figs. 2 and 3 after a severe one moved through Tennessee. The first image documents wind damage. The tower was swaying back and forth as Chris took the pictures; eventually the hanging section broke off. It was gone several days later. A number of nearby homes also were damaged in the storm.

Fig. 2: Mother Nature takes a swipe at an AM tower. The top section eventually broke free.
Fig 3: Fortunately, the site was not in use.

Fortunately, the AM structure hasn’t been used in a number of years, as suggested by Fig. 3.

Next time you head to the transmitter site, blow up one of these pictures on the copy machine. Tape it to your office door with a note: “Gone to check the transmitter site!”

* * *

Fig. 4: This ‘Euro’ connector has a screw that pushes down on a brass tab within the port. The tab makes contact with the wire.

Wayne Eckert is president of Channel 1 Images. He offers a point of clarification about our “green trumps white” segment at the end of the July 1 Workbench.

The white “Euro” connector does not in fact have a screw that makes contact with the wire. Instead, the screw pushes down on a brass tab within the port of the connector, which in turn makes contact with the wire, in a manner similar to a Phoenix connector’s. As such, it will not damage the wire in the manner described.

Contributor Paul Sagi writes that he enlarged the photo of the connector and found the construction as described. Paul goes on to say that the connectors he buys from supply houses in Kuala Lumpur lack the brass tab.

Wayne and Paul bring up good points. In an effort to lower manufacturing costs, some vendors may lower the quality of their components. Check parts carefully.

Contribute to Workbench. You’ll help your fellow engineers and qualify for SBE recertification credit. Send Workbench tips to johnpbisset@gmail.com. Fax to (603) 472-4944.

Author John Bisset has spent 43 years in the broadcasting industry, and is still learning. He works for Tieline Technology, is SBE Certified and is a past recipient of the SBE’s Educator of the Year Award.


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