Solved

LCD TVs - What would generate a 1110Hz (audio) pitch?

Posted on 2014-03-28
2
197 Views
Last Modified: 2014-04-16
We have a new soundbar ($200 range, middle of the road as these things go).
Unrelated, due to various factors we must use the Earphone-out jack from the TVs.
We realize that this is not optimal impedance matching, but it's not a high-end home theater situation.

What about two different brands of flatscreen TVs (Sceptre, LG) would BOTH generate the identical 1110Hz pitch picked up by the soundbar amp/spkr?
Is there an internal scan line frequency or refresh rate that coincidentally is the same in both TVs?  (maybe a uproc or switching pwr supply  clock frequency?) -- something whose EM field is unshielded or un-notch-filtered.
I've tried all combinations of off/unplugged, and it's only when the one isolated TV under test (connected to the soundbar) is plugged in that the pitch is picked up WHETHER THE TV IS "ON" of "OFF" (i suspect a standby mode). Also, it's the same regardless of TV input source selected (HDMI vs AUX vs TV RF tuner).  Also high-end earphones pick up nothing.

In trying another non-TV device earphone-output jack (my laptop was handiest), there is no pitch (i would have expected the laptop to have more rogue unfiltered/unshielded emissions going on),  thus it's not the soundbar's fault.

We can live with the SNR mitigated with TV volume loud and soundbar volume low, there's no distortion.

But i'm curious why exactly 1110Hz,  between two brands.
0
Comment
Question by:willsherwood
2 Comments
 
LVL 20

Accepted Solution

by:
CompProbSolv earned 500 total points
ID: 39962817
My first suspicion is some sort of grounding problem.  Headphone jacks are typically designed to connect to passive devices that have no ground (or other power) connections.  That would explain why headphones or a battery-powered laptop wouldn't exhibit the problem.

I'm afraid that I can't explain the actual frequency.  My first guess would be that it has to do with the switching power supply in the TV, but I believe that those run at much higher frequencies than that.

Is there any chance you can use a different output, such as line-level or optical?  If not, some sort of audio isolator may be appropriate.
0
 

Author Comment

by:willsherwood
ID: 39962860
thanks for your comments- the optical output jack for the TV is broken (we didn't discover until too many months too late), i suspect it would be fine.
i hear you about passive... (low impedance)
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

As more and more media become available over broadband Internet, a common question is:  How can I watch these movies and TV episodes (eps), anime, YouTube subscriptions, etc... on my big-screen TV?   Why limit your viewing experience to the small…
I don't watch much broadcast TV directly (I hate commercials), but I do have an extensive library of video files (movies and TV episodes) on my PC's hard disk.  When I got my new Toshiba HDTV, the first thing I did was hook up the "PC Interface" as …
Sending a Secure fax is easy with eFax Corporate (http://www.enterprise.efax.com). First, just open a new email message. In the To field, type your recipient's fax number @efaxsend.com. You can even send a secure international fax — just include t…
Both in life and business – not all partnerships are created equal. As the demand for cloud services increases, so do the number of self-proclaimed cloud partners. Asking the right questions up front in the partnership, will enable both parties …

912 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!

Get 1:1 Help Now