What Are the Cylyndrical Objects You Often See on Audio, USB, etc, Cables?

"Nelson" schreef in bericht news: snipped-for-privacy@news.astraweb.com...

They are ferrites and used for RF suppression. You can buy types that can be clamped on existing cables and they usually are effective. Nor that expensive too so it's worthwhile to give it a try.

petrus bitbyter

Ferrite cores

Jeff

Regulatory repellents. They're attached by the manufacturer to keep the FCC off their back by limiting the amount of RFI/EMI sprayed by their equipment.

Yep. Under the nearly impossible to remove plastic cover lies a heart of powdered oxidized iron.

Quite well. If an FCC Enforcement Burro inspector approached, all one needs to do is wave the lumpy cable at the inspector, and he will vanish into a smog of legalese.

Oh well. You finally decided to disclose what you're trying to accomplish, so I guess I'll have to provide a reasonable answer.

I assume the computah generated interference is trashing the picture on the TV or is being heard on the TV audio. What channel is the TV watching? If it's channel 3/4 from some kind of set top box, you might find it more useful to simply avoid the RF problem and rewire your TV setup to use a non-RF input. HDMI, DVI, component video, S-video, and component video inputs should all be present on the back of your unspecified model TV.

If you're only using the TV for computer audio, you could also eliminate the problem by purchasing a set of "computah speakers" for about $30. The speakers inside most TV's are fairly disgusting.

If none of these alternatives seem useful, you can purchase clamp on ferrite filters.

Radio Shock carries some:

or you can just cannibalize the ferrite beads off an old cable. For audio, just about anything will work. Bigger is better and running multiple turns through the core is even better:

Gotta run... good luck.

Do what Jeff says. As past predident of the IEEE EMC Society, I have used many ferrite beads to reduce interference levels to meet FCC requirements. There are cylidrical beads for round cables and flat beads for ribbon cables. If you scrap almost any piece of electronic equipment, you can scrounge a ferrite bead or several.

But, there are different compositions of ferrite to cover the whole frequency band, so the first bead you try might not be the one you need. If you told us a little bit more about what your setup is and what the interference is and where and what you turn off to clear the problem, we might be able to give you a lot more help

On Wed, 9 Nov 2011 17:02:18 -0500, snipped-for-privacy@att.net wrote (in article ):

That reminds me... my IEEE Life Insurance premium is due. It was such a bargain when I was younger :-)

I have a MacBook Pro set up as an entertainment center feeding an analog TV. Video is out of the mini-display port through an S-Video adapter. Audio is out of the headphone port into the RCA audio-in on the TV. There is a constant hiss which modulates with screen changes. Since I don't hear the hiss if I just connect earphones to the port, my assumption is that it is RF pickup from the S-Video cable or the TV being fed back through the audio cable. If any of my classes ever covered RF interference, I must have slept through them :-)

I posted this problem here a while back. One suggestion was to buy a usb or firewire sound adapter... but my insurance premium is due :-) And, besides, there is no way to test it in advance to see if it solves the problem. Another was to try to wrap the audio cable around a ferrite core. I pulled one that looks like a washer off an old piece of equipment and took a few turns but nothing changed. I also considered grounding. But the Mac runs off the battery so it's not clear how I could force a common ground. And I'm a little leery of that anyway having fried one or two things in my younger days trying to establish a common ground to an oscilloscope :-)

I have an audio cable with a sub-mini-jack at one end and two RCA jacks at the other which has one of these ferrite things at the mini-jack end. Unfortunately, it is the wrong size for the earphone port, but it got me to thinking. On my list of "to do's" is to go down to Radio Shack and buy an sub-mini to mini adapter so I can try out the cable but I'd like to figure out what the actual problem is before throwing money at trial and error solutions.

Fix your earphones. I've heard the hiss on several Macbooks.

I remember. Same problem, same suggestion. The MacBook audio output is noisy. Ferrites are not going to fix it.

As for the cost, is $1.30 too much for you?

More on the hiss problem.

My guess(tm) is some manner of internal grounding problem. The his is probably coming from processor switching noise, some of which is going through the audio circuitry. Ferrites are not going to fix that. Spend the $1.30 and get an external USB or firewire sound thing.

On Fri, 11 Nov 2011 11:46:45 -0500, Jeff Liebermann wrote (in article ):

OK, OK, I spent the $ 1.30 :P I'll let you know when the slow boat from China gets it here. But I thought you said earlier that you tried USB and it didn't work. Do you have any $1.30 firewire solutions up your sleeve? :-)

On Fri, 11 Nov 2011 11:37:37 -0500, Jeff Liebermann wrote (in article ):

Not to be argumentative but I just hooked up a set external speakers to the audio output jack and cranked the volume up to Pain Level 1 and could not detect the hiss. I tried with with the speakers powered by 6 AA batteries and with an AC adapter. No detectible difference.

Unfortunately this is not a solution because then my wife can't control the volume with the TV remote.

There are others available from domestic sources on eBay. I happened to find the absolute cheapest.

Correct. Thanks for reading what I previously posted. However, you missed or forgot an important point. We were trying to use the MacBook for recording a music festival. The hiss was also present with USB on record as well as playback. For playback, I doubt if you could hear hiss that was more then -30dB down from the peak audio level. That's 1/1000th of the peak volume. However, the recording engineer wanted absolutely no buzz or hiss at any level. I couldn't do that with the USB dongle. I got close with fancy USB external sound card. However, when someone air dropped (literally) a firewire sound card, the noise was almost totally gone on the spectrum analyzer.

Note that in a previous URL, various users offered different grounding, ungrounding, configuration, and equipment changes to fix the hiss problem. Reading further, most came back indicating that the fix was not permanent.

No. I'm wearing short sleeves.

Do your own shopping:

These look like the cheapest and can probably be found used somewhere:

On Fri, 11 Nov 2011 23:44:50 -0500, Jeff Liebermann wrote (in article ):

I always read what you post :-) I am appreciative of anyone who takes the time to help me and I have always found this group to be exceptionally knowledgeable and willing to help (as opposed to some other groups I belong to who offer only snarky comments).

Indeed, I _did_ miss that.

Perhaps all instances of the symptom don't have the same cause.

tZ5781QQufmZ1QQugatZ2QQuqtZrQQusopZ1003>

I think I'll hold off until I see how the Chinese USB dongle works, assuming the company actually exists :-) It's hard for me to imagine how they can even afford to ship it at that price. No wonder they are killing us.

I am still struggling to explain why the hiss is very loud when the audio output is connected to the TV and inaudible when connected to earphones or the external speakers. I'm thinking that maybe the S-Video ground and the audio ground are at different levels. But then you had the problem with no video output involved, right?

As I vaguely recall, the USB dongle didn't have much noise when the laptop was running off battery, but was slightly noisy with the AC adapter attached. I had 2 or 3 different USB audio dongles, which were about the same.

You might try ordering from a USA vendor for faster delivery:

Agreed. If you purchase such a dongle retail in the USA, my guess is that it would cost about $15. As long as we have enough money to purchase such underpriced products, we will benefit from the low prices. When we run out of money, China will own us.

It doesn't require video to produce the hiss. My guess(tm) is that it's coming from the processor, not the video. Changes in operating configuration and wiring produce a different path to ground for the processor. It it happens to go through or near the audio circuitry, you get hiss. If I knew which ground path, it might be possible to do something to fix it. However, the easiest fix is to insert something that isolates the audio ground from the laptop ground. I don't know if the USB dongle or the other devices do this, but it would make sense to prevent ground loops.

On Sat, 12 Nov 2011 14:05:21 -0500, Jeff Liebermann wrote (in article ):

=1&_sop=15&_sticky=1&_trksid=p3286.c0.m301>

Well, the Chinese Dongle arrived and seems to work fine. But it has zero effect on the hiss. At least it has a nice green flashing LED to let you know when a signal is being transmitted :-)

Guess I'll just have to live with it.

On Sat, 12 Nov 2011 14:05:21 -0500, Jeff Liebermann wrote (in article ):

=1&_sop=15&_sticky=1&_trksid=p3286.c0.m301>

Update: So I got one of those new-fangled Digital TVs with an HDMI input. Unfortunately the Mac only outputs video on the HDMI interface so I had to use the Audio Out RCA jacks for the sound. Fortunately the TV accomodates this. Result: No Hiss.

Summarizing my observations:

S-Video + RCA Sound to Analog TV - Hiss S-Video + USB Dongle to Analog TV - Hiss S-Video + External Speakers - No Hiss S-Video + Earphones - No Hiss HDMI + RCA Sound to Digital TV - No Hiss

The conclusion I draw from this is that the problem is not the MAC but RF interference picked up by the analog TV.