Radio signals when recording - ANOTHER UPDATE

Peter,

Keyboard? Is this your PC keyboard, or something else?

Radio signals? A local station? Can you determine which radio station it is?
And what frequency it broadcasts on?

Do you get the same signals with nothing connected to your soundcards, if you
try and record with the input gain levels turned up?

Sorry for all the questions, but it could be many things.

Regards,
Colin.

Greetings Peter,

RFI --- radio frequency interference is an awful enemy. That stuff sneaks in where it's least expected.

EDIT: This kind of interference is always a local AM radio station. The amplitude modulated signal gets rectified by a diode (just like the crystal radios of yesteryear) and amplified by your preamp.

Actually I am surprised that it gets into a modern well-designed keyboard to ADC connection! Try using short, high-quality, cables (and I don't mean Monster) but just not the cheap junk that is shipped for free with equipment. These cables should be called double-shielded with a greater than 95% coverage braided shield and a foil shield around that.

If that doesn't work, then you can try the RFI suppression beads (like the ones that form the lump in your monitor cables).

If that doesn't work, you might consult a copy of the ARRL Amatuer Radio Handbook. They have been causing, and helping to fix, RFI interference for 100 years, so they know some pretty good techniques.

Good luck!

Regards,
David

PS, the best approach is to create a Faraday shield by wrapping your entire room in aluminum foil like some guy I read about years ago. I think he's in a safe room with a different kind of wrapping now. On second thought, maybe this isn't a good idea...

Thanks dcastle.

Wow! That is some deep, deep stuff. Looks like I'm going to have to do some research before I can decode your last response. LOL That's way over my head.

I do understand some of what you're talking about and I can print off your posted response and start researching to figure out the things I don't understand. I can then try your suggestions.

I envy your knowlege! Thanks again.

Yeah, make sure you're not using speaker cable! :D I did that once and I could literally listen to the radio program... every word.

Make sure whatever cables you're using are sheilded. Either that or wrap your room in tin foil and ground it... :P

Well, from the responses it's apparant that the problem exists because I'm using speaker cables.

Do they make sheilded cables with RCA plugs?

And if not, then could I use sheilded cables that have 1/4" plugs and add an RCA adapter plug to the end that connects to the keyboard? Or would the RCA adapter connected to the sheilded cable still pic up radio interference?

Bingo ! I think we just found the problem. Am I a good guess or what ?

If the outputs of the keyboard are for speakers then you will also need attenuating patch cords (also shielded) or attenuating plug adapters. Radio Shack should have those also. Or in a pinch you can try turning the volume WAY !!! down on the keyboard if you can't find the attenuaters. When setting your record levels turn the volume all the way down on they keyboard and turn it up by tiny amounts till the levels look good in Sonar. You may get lucky and the outputs will be line level but start off very low just in case they are speaker outs. And yes, almost all RCA to RCA cables are shielded, you just happen to have some old style speaker cables. Most modern stereos don't even use them anymore they have spring loaded clips that use bare wire. On old stereos from the 70s and early 80s some did still use RCA plugs for speakers so many folks still have those unshielded cables around the house but they are not to be used for line level connections or you will pick up all kinds of noise and radio stations.

Exact problem with me too.

I am having an older Yamaha PSR-540 that picks up radio signals when its on. The signal get stronger if I touch the speakers of the keyboard.

Fortunately, it happens only when the speaker is placed in one position in the room...I moved it to another location in the room, recently, and the signals disappeared...

rhythmeus

The new sheilded [sic] cord did not eliminate the radio signal but seemed to lower the volume of the radio station from -50db to about -40db.

Oops! -50db to -40db is an increase of 10db. This is very bad. It seems to indicate that the radio station is sneaking in some other path.

Check the input routing on your ADC interface. Maybe you accidentally have an open input being summed along with your desired input.

Unless you are right next door to a huge radio antenna (in which case you should move for a variety of reasons), you shouldn't be getting any radio station bleed into any of your analog signals.

Regards,
David

OK. Here's what I've discovered so far:

1. Replacing the keyboard's non-sheilded cable with a sheilded cable had no affect on the radio signal. I was mistaken in my earlier post.

2. The radio signal stops when the cable is disconnected from the keyboard even when when the cable remains connected to the preamp. This indicates that the signal is not coming from the cable.

3. The radio signal still bleeds through whether the keyboard's power is on or off as long as the audio cable is connected. The same thing applies whether the keyboard's power supply is plugged in or not.

4. When I connect the MIDI cables to the MIDI outputs of the keyboard it greatly reduces the volume level of the radio signal when the audio outputs are also connected.

5. It appears that the keyboard is in someway working together with the preamp to pick up the radio signal. If I plug the keyboard's audio cables directly into the soundcard, thereby bypassing the preamp, the radio signal stops. However I can only achieve a maximum -20db level of the keyboard using this method. If I record the keyboard using this method and then playback the track I can not hear the radio signal even if I increase the Trim level to the maximum +18 on the track. However by increasing the Trim to its maximum I can achieve a -7db level when playing back the recorded track.

6. If I move the keyboard to different areas of the room it affects the radio signal. In some areas it makes it louder and in other areas it begins to pic up an additional radio signal so I get 2 stations playing at once.

7. If I get very angry and put my foot through both my monitors the radio signal stops. Unfortunately so does all other audio.

If I go back and re-read some of the suggestions on this post that were beyond my comprehension I may be able to figure this out.

Based on what you described the keyboard it'sef is acting as an antenna.

Try grounding the case.

Thanks MysticMizer.

I was thinking the same thing about grounding the keyboard. However I can't seem to figure out how to do this. The entire casing of the keyboard is plastic. And the screws that hold the plastic casing together screw into other plastic parts.

And here's dcastle to my rescue again. LOL

As a matter of fact the power supply for my keyboard is only a two pronged plug. As far as the socket goes, I purchased this home about 2 years ago. The home is 50 years old and did not have any grounded sockets throughout the entire house. I replaced all the 2 prong sockets with 3 prong sockets. I connected a ground wire from the socket to the back of the housing that the socket attaches to. I'm not an electrician so I don't really know if that worked for grounding the socket. The housing is nailed to the wooden studs of the wall. But I'm thinking that this does not constitute proper grounding techniques.

The picture of the RFI filter that you posted looks interesting and I think I might see if I can locate two of those. Perhaps one for the left cable and one for the right. It's worth a shot and it doesn't seem like they'd be that expensive.

Thanks again.

I replaced all the 2 prong sockets with 3 prong sockets. I connected a ground wire from the socket to the back of the housing that the socket attaches to.

Nope! That's not grounded. You've got to get that ground wire to a cold water pipe somewhere. You can get a pipe ground clamp from Home Depot like this



Regards,
David

BTW, make sure it's a cold water pipe, there have been terrible stories about people connecting grounds to gas pipes, which doesn't make any difference until there is a castrophic failure, and then there can be a really catastrophic failure!

I would suggest at the very least setting up a grounded plug in your recording room (do the water-pipe thing as suggested above) and make sure you use a #12 or larger stranded wire for the ground.

Remember that wire gets larger when the gauge gets smaller (and they don't use the "#" anymore) so an 8 gauge wire is larger than a 12 gauge wire.

Regards,
David

BTW, for radio signals, the ground is going to have to be shorter than 10 feet or so. Otherwise the ground connection can act like its own antenna and actually make your situation worse. This doesn't usually happen in a house because the ground is physically near the hot/neutral connections and forms a psuedo balanced connection as far as RFI is concerned. Adding a ground wire to a receptacle like you have is an important safety precaution, but unless it's short, it won't help your radio interference problem.

Guys you're not listening. The keyboard doesn't have a ground pin. When he plugs it into his sound card he is making a high impedance ground connection through the sound card that is turning the keyboard into an antenna. These two prong setups are what is referrred to as double insulated meaning the power side of the supply is galvanically isolated from the instrument side of the supply. As long as it's floating there's no place for the current generated by the RFI to go so there's no problem. Ground one side of the instrument through 20~30 ohms and float the other through a high impedance and you have a fine loop antenna. I think the only thing you can do is use a transformer direct box to isolate the keyboard.

All the other suggestions would be useful if you had a regular keyboard with a three pin power plug but in this case I don't think they apply. Well possibly the RFI filter which is just a big ferrite bead.

Dan

I guess I am old, but we still use the "#" for short-hand to mean "gauge" in the sound industry, and it also shows up on all of the elctrical drawings that we get from the contractors/consultants/architects, but that's not important now: get a new keyboard or sound module.
This will at least fix this problem, and the fact that (a) the keyboard itself is the only part of the system that is providing the RF issue an (b) a used keybord/module from eBay might cost less than the solutions mentioned, it would probably save you a lot of wasted effort and/or money.
The truly sad thing thing about all this is the fact that you can do everything discussed here and still have problems, when your neighbor does nothing "by the book" and has no issues whatsoever.
Good luck!