It can be difficult to keep out strong radio broadcast signals, especially when the mains earth to your apartment block will have to travel nearly all the way up to the top of the building.

Top marks for doing the foil-lined drawer experiment! It demonstrates that the problem is primarily electromagnetic in nature rather than mains-borne (conducted).

Can you tell us which model of Focusrite you have, and whether it is USB-powered or has an external mains power supply? The Presonus Bluetube pre-amp is separately mains powered, but does its power supply have a 3-pin mains plug so that it gets an earth connection? When you connect the Bluetube to the Focusrite, Do you use a balanced cable (two signal cores with outer screen)? Which Bluetube output socket and Focusrite input socket do you use for this connection?

PS none of your attached pictures is accessible (at least for me). The icons are all crossed out in red.

Hey Boswell. First of all thanks for answering so romptly.
Those are the images.

Drawer experiment
Cable shielding experiment

My Focusrite is a Thunderbolt powered Saffire Pro 26

And my signal chain is Guitar UNBALANCED p10 ----- BlueTubev2 ---- UNBALNCED p10----Focusrite

My Bluetube is using a Powerchord to a. external power supply that only has two pins.

I use Channel 4 for Focusrite input, which I believe is combined XLR + P10 input.
And I use channel 1 unbalanced output in Focusrite.

Please lemme know if you need any more info, I would be glad to provide it to. you :D

RFI interference is interesting. The fact you can hear the music and identify the station is a clue, but a very strange one. FM - the most common modern mode is very difficult to detect - but if you have the broadcast station on your roof running lots of power, it can easily get into your audio system. For many years, a guy called Jim Brown has been a US authority on these things - here's a link too a heavyweight document that does have some solutions you can try. http://audiosystemsgroup.com/RFI-Ham.pdf

Essential the interference gets in, and your system is detecting it - as in converting it back to audio. The usual solution involves finding out where it is getting in, and then putting a barrier to block the interference, before it gets to the part of your system that is detecting it! Your drawer experiment shows you can stop it, so the next step probably would be a bug ferrite ring on the cables leading into the system.

Your last post and your photos give a clue to the problem: unbalanced cables. Your experiment of wrapping the connecting cable in foil turns it into a form of twin-conductor-in-a-shield cable, giving an improved result. Before you go any further, please try a proper balanced cable that uses TRS plugs rather than TS. (T=tip, R=ring, S=screen/shield)

Running the Bluetube in the form it was supplied (2-prong mains PSU) is not going to help matters. About the only thing you can do about that is to run a separate ground wire from the Bluetube chassis to mains earth. The combination of Thunderbolt cable and a TRS connecting lead should do this for you, assuming the Thunderbolt plug carries a good earth from the computer, and that the computer is properly earthed.

Boswell, post: 466437, member: 29034 wrote: Your last post and your photos give a clue to the problem: unbalanced cables. Your experiment of wrapping the connecting cable in foil turns it into a form of twin-conductor-in-a-shield cable, giving an improved result. Before you go any further, please try a proper balanced cable that uses TRS plugs rather than TS. (T=tip, R=ring, S=screen/shield)

Running the Bluetube in the form it was supplied (2-prong mains PSU) is not going to help matters. About the only thing you can do about that is to run a separate ground wire from the Bluetube chassis to mains earth. The combination of Thunderbolt cable and a TRS connecting lead should do this for you, assuming the Thunderbolt plug carries a good earth from the computer, and that the computer is properly earthed.

Thanks again. I'm going to buy cables today. So, just to be sure. I can try connecting a wire from Bluetube chassis to Focusrite chasis?

Try it first with just the TRS cable. This is an example where RF screening can be really important.

You didn't say what type of computer you had, and whether it was earthed.

Linking grounds like this usually either makes it better or worse - and won't hurt, but do remember that the purpose of grounding is NOT to stop hums, it's to save your life. In most cases, making it safe, makes it quieter - but there have been cases of where casual extra grounding can be problematic. However - devices fed from wall-wart style power supplies often don't actually have a real ground anyway.

Interference reduction/removal usually benefits from good grounding - but most audio kit gets grounded by the audio cabling. Just remember multiple ground paths in audio are generally bad - but in a small studio, there's often only one real ground anyway.

My warning is really for people who like to ground their systems to radiators, water pipes etc. Just remember that the water main ground in a tall building can be very different potential wise to the grounding of electrical outlets. If there is a 4 Volt difference - and you do extra grounding, you are sticking 4 Volts at 50/60Hz INTO your nice quiet audio system. When a fault occurs anywhere in the building that could also be an awful lot of Amps trying to get from the electricity outlet ground to the water main ground THROUGH your audio system. This is why people often advise against it, but loads of people do it. General best practice is to be careful and if you are unsure on electricity, ask somebody local you trust. I hate being the doom and gloom merchant, but I still have a scar on my hand from this going wrong when I was in my 30's!

Boswell, post: 466459, member: 29034 wrote: Try it first with just the TRS cable. This is an example where RF screening can be really important.

You didn't say what type of computer you had, and whether it was earthed.

I am using a macbook. But the power out let is just two pin. My building wall outlet is grounded though.

Gus Machado, post: 466461, member: 49963 wrote: I am using a macbook. But the power out let is just two pin. My building wall outlet is grounded though.

The Focusrite Saffire Pro26 also runs off an external 12V PSU, so there's a good chance that nothing in your audio chain is connected to mains earth. In addition to using TRS cables, I would try an earth link from (say) the Focusrite chassis to a ground pin of your wall outlet.

Some of these experiments may not have much effect on your radio breakthrough, others (or combinations) could bring it down to an acceptable level. Remember that the interference is not originally at audio frequency; whatever's interfering is a radio frequency, and this is being rectified by active devices (valves, diodes, transistors etc) in your audio setup down to audio. That makes it unlikely to be an FM band transmitter, as FM usually interferes as whistling noises, but there could be other transmissions going on from all those aerials on your rooftop. Have you ever identified the interfering audio that you get with what is playing at the time on a local radio station?

Boswell, post: 466462, member: 29034 wrote: The Focusrite Saffire Pro26 also runs off an external 12V PSU, so there's a good chance that nothing in your audio chain is connected to mains earth. In addition to using TRS cables, I would try an earth link from (say) the Focusrite chassis to a ground pin of your wall outlet.

Some of these experiments may not have much effect on your radio breakthrough, others (or combinations) could bring it down to an acceptable level. Remember that the interference is not originally at audio frequency; whatever's interfering is a radio frequency, and this is being rectified by active devices (valves, diodes, transistors etc) in your audio setup down to audio. That makes it unlikely to be an FM band transmitter, as FM usually interferes as whistling noises, but there could be other transmissions going on from all those aerials on your rooftop. Have you ever identified the interfering audio that you get with what is playing at the time on a local radio station?

Yes, but the Focusrite ins being powered only by the thunderbird connected to the mac.
It is playing radio, because sometimes I listen to music and and voiceovers. It is a Radio that stays 7 minutes from my house, FM 107,9 is that your question?

Hang on - is the radio station transmitter on your building? What we are talking about here is direct radio frequency induction into the system you have, and this means close - very c lose actually, even with moderate local radio powers. 7 minutes away? As in 7 minutes walking, driving or running TO THE TRANSMITTER, not the local studio? I was under the impression you were one floor below loads of radio equipment? Remember that RF energy dies away with the inverse square law. Double the distance and the power drops to a quarter, double it again and it's a 16th of the original strength - a few floors make a difference. Hopefully the tips here will cure it for you. What is a bit unusual is that FM broadcast radio rarely allows music and voices to be heard - it's usually noise and buzzes. AM radio would often allow voice to be heard with music, but much, much rarer to get music detected from high signal strengths. There could be something more interesting going on?

paulears, post: 466464, member: 47782 wrote: Hang on - is the radio station transmitter on your building? What we are talking about here is direct radio frequency induction into the system you have, and this means close - very c lose actually, even with moderate local radio powers. 7 minutes away? As in 7 minutes walking, driving or running TO THE TRANSMITTER, not the local studio? I was under the impression you were one floor below loads of radio equipment? Remember that RF energy dies away with the inverse square law. Double the distance and the power drops to a quarter, double it again and it's a 16th of the original strength - a few floors make a difference. Hopefully the tips here will cure it for you. What is a bit unusual is that FM broadcast radio rarely allows music and voices to be heard - it's usually noise and buzzes. AM radio would often allow voice to be heard with music, but much, much rarer to get music detected from high signal strengths. There could be something more interesting going on?

Só muh deep info I promise I will take time to assimilate. Thanks me.
I guess I expressed myself poorly. So here it goes again:

I live in the 9th floor. On the top of my building there is a lot of antennas that I don't know why are they for.

2,9 km of my house. (I live in the highest part of Sao Paulo ), there is a Radio station.

I'm going to try changing all my cables to balanced ones first and see what happens.

The location of the transmitter is the vital part - the radio station is simply on the end of a piece of wire or fibre. Local radio often use roof space on modesty tall buildings. Do you know the frequency the station operates on, as you recognise it?

paulears, post: 466467, member: 47782 wrote: The location of the transmitter is the vital part - the radio station is simply on the end of a piece of wire or fibre. Local radio often use roof space on modesty tall buildings. Do you know the frequency the station operates on, as you recognise it?

There's is a huge antenna o the radio building. I CHECKED on google street view. It is 107,9 FM

If it is local radio, then the service area will be moderate - maybe only ten miles or so around your location. Area stations tend to be located on hilltops to get more coverage. Local radio is unlikely to have more than 250W or so of power, but this is enough at 10m or so, to get in where it shouldn't. Please let us know when your new cabling is in.

paulears, post: 466469, member: 47782 wrote: If it is local radio, then the service area will be moderate - maybe only ten miles or so around your location. Area stations tend to be located on hilltops to get more coverage. Local radio is unlikely to have more than 250W or so of power, but this is enough at 10m or so, to get in where it shouldn't. Please let us know when your new cabling is in.

I'll be back home in a while with the new cables I just built. A d keep you guys posted.

I dunno what do you mean by local radio. I mean Being Sao Paulo a 22 million inhabitants city, and being this a city radio...

Radio stations can cover wide areas or local radios - I checked and your country has both kinds. If you are in the centre of the city, then 10 storeys is not a hugely tall building unless you are own a hill, with the surrounding areas lower. If you have a city wide transmitter above your head, then distance is quite critical as it's going to be considerably higher in power. Fingers crossed on the cables.

Ok guys, here is the veredict: it improved, I have a better ratio volume/interference. But it is still there, and it is unbearable yet.
I think I should tried the ferrite stuff now, right?!

Tried the ferrite bead. Maybe it is less noisy now, but I still getting some sort of the signal.

Remember the little ones are probably not effective - have you tried the big one, and multiple turns.

Guys, thanks again.
So yeah, did some further tests

1 - balanced cables helped like 10% (not much than this)
2- Ferrite beads helped almost nothing, sonI can't tell the difference - maybe it's psychological.
What did helped a lot, like 95% better WAS USING A DIRECT BOX.

So here is what I did:

Used a 15 cm unvañanced gable, connected to the hiZ input of a directbox - yes a short cable, so it doesn't have much contact surface to work as an antenna and a balanced xlr cable going from the DI to the BLuetube preamp, the. Another short xlr cable, 15cm, from the preampmto the Interface. Remembering that both the interface and the preamp are inside the home made Faraday's cage I've built inside a drawer.

After this my noise is about -50db, and is not distinguishable anymore, it only sounds as static. Something easily treatable with Izotope RX + noise gate.

So here's my next question: what about my condenser mics, because I can't use the same strategy on them.

The trouble is, you haven't solved the problem, just hidden it. When you use the condensers, what happens?

paulears, post: 466499, member: 47782 wrote:
The trouble is, you haven't solved the problem, just hidden it. When you use the condensers, what happens?

I know right? But as long as it allows me to record line instruments without EMI, it is already a step further. The definitive solution (building a cage doesn't seem a simple one).

Based on what I tried so far is there any solution (like the DI box I used for line signal) for condensers mics?

RFI reduction is always a temporary solution. We constantly buy new gear, or a friend comes round with his new guitar and plugging it in creates hell. Condenser mics actually are normally less trouble than dynamics. In your system, the snag is you have not identified where in the chain the RF is being detected. We've not even ascertained if the interference IS from the antenna on the roof. FM radio is much, much harder to decode as audio. AM is easy - almost any semiconductor can do an excellent job of demodulating AM. Getting understandable audio from FM is more difficult - the usual process is slope detection, but it's not easy to do deliberately, let alone accidentally as appear to be happening. Can you find out what you have on the roof - the building owners will know, because contractors will visit for maintenance and the owners should be aware. If you can get up there, they also normally label everything. For long term recording, you'll need to determine which bit of kit is your problematic one. It could be a fault? Most modern equipment has EMC components and maybe these are faulty, or non-existent? In my office I have a marine transponder on 24/7. I have antennas right outside the window. I get no interference at all, and the field strength maybe be higher than your situation - my 25W close to my audio kit could well be stringer than your possible 1KW, two floors above.

I'm a little surprised that your building - which is only of modest height for a city - would have an area transmitter on it. ~The height required to do more than just a few miles seems to be a mismatch for anything attempting longer distances. Round here we have a local radio station - with 25W output and it manages maybe 6 miles reliably to vehicle radios. The area radio stations are running more power and on a 50m tower, on the top of a hill about 25 miles from here and it's marginal in places.

You need to work out where in your chain of equipment the susceptible component is, and then take steps to sort it. If you don't have the means to do it, search out the local radio ham club in your area, and ask them for help. They will have the equipment and the expertise to help, if you ask nicely.