Attempting to Record LFN.. Help!

Hello

First let me apologise for the long post, I have attempted to include as much pertinent information as I am able, and as a result it has continued to grow. Secondly, I must admit to my ignorance of sound; let me say that I find the whole subject as perplexing as chemistry, so please be patient.

The problem I have is that I am plagued at night by a Low Frequency Noise (LFN) which constitutes an incessant pulsing but at a low volume. (This has been going on now for some three years and I am truly exhausted through the lack of sleep). I have ask the local council to help, but they have no real idea how to assist, and I have spoken with several sound consultants (but their fees are extraordinary and quite simply out of my league); nevertheless, they have confirmed from my description it is indeed a LFN; several visitors to my house have also confirmed that what I am hearing is not a fiction or an aberration of my hearing (the LFN is only audible within the property).

The sound is able to travel through walls and remain at a constant volume from one side of the property (a small cottage) to the other.

I have made many a search on the internet and found a video of a guy who has a very similar problem https://www.youtube.com/watch?v=hBi-rtWd-yA, so in an attempt to copy his example I bought the following:

Behringer ECM8000 Omnidirectional Measurement Condenser Microphone (15hz to 20 khz)

Stagg SMC6 6 metre standard microphone cable

Chord (UK version) Phantom Power Unit 173.077UK

LogiLink USB to XLR Microphone Adapter Cable

Which I have plugged into an iMac (Mid 2010- OS 10.8.2) and use Audacity (2.0.2) to try and record the noise. (System Preferences/ Sound/ Input/ Input Volume maximum), I might add that the iMac is in a different room from the microphone in an attempt to isolate the microphone from any noise that the computer might make.

To be honest playing any of the recordings of the LFN at normal volume just produces a quiet hiss; nevertheless, after making my recordings then using the example on the video, I have played around with the equalizer (I don’t know what I am doing, just sliding sliders up and down) and found that if I slide all the sliders down then slowly go from one end to the other moving each slider in turn to listen for any sound I have found that between 61Hz to 100Hz I can hear a noise, at first this was exceptional as I thought I had cracked it and could take my findings to the council and ask them to investigate as they have refused to investigate given they are unable to hear the sound.

However, on the few days there has been no LFN and the house has been still (that is to say: no central heating, no TVs or Radios; I live in a rural area so there is very little regular traffic noise, no power lines, or tunnels underground, nor aeroplanes/ flight paths and given the length of time that this LFN lasts (anything up to 8 hours)) I can rule out transport) I have made recordings using the same method as described above, then following the example from the video, unfortunately I still get the same noise once I apply the equalizer, which cannot be right, if I cannot hear it why would I be getting the same result when I have made recordings during those times I do hear it? So I must be doing something wrong with Audacity.

I will attach two recordings one where I can hear the LFN and one where (as far as I am concerned) there is silence and I wonder if any of you might be able to help, surely the microphone should be able to capture a sound if the sound is above 15hz (from what I read our ears can only hear down to about 20hz, but if the LFN is at 60hz, 100hz or 150hz or anywhere in between so surely by increasing the system volume to maximum then adjusting the equalization sliders I should be able to isolate it?), regardless of if that is so, why am I getting the same result with two different recordings?

Both files are 8 second clips Exported from Audacity in WAV (Microsoft) signed 16 bit PCM (I have no clue what that means, but I hope it will suffice).

So after all that, if you know a way I can capture the LFN with the equipment I have, or indeed if I have captured the LFN and you know a way to help isolate it beyond that which I am currently doing then, well let me put it this way, that will be extremely decent of you.

I pulled both sound clips down. I amplified both of them about the same amount in order to supply something of good volume to get on with. Effect > Amplify > OK.

Then I applied Effect > Low Pass Filter, 36dB, 60Hz and then again starting over at 36dB, 40Hz.

I can’t tell any significant difference between the two sound clips. On my killer sound system, it sounds like a lorry or a tube train going by and if I make it loud enough, I can see the wine glass start to walk across the table. Entertaining, but both sound clips do it.

Unfortunately, Audacity doesn’t adjust its tools in real time like the guy in the YouTube video. We’re not Cool Edit. You can’t slide the equalizer controls up and down and immediately hear the effect.


Do you have your Chord phantom power device switched to 48Volts? That is required. The other Chord voltage option will not run the microphone. Turn off everything before you switch it if you need to. It can damage the microphone if everything is running when you do.

You did say something that has not been my experience. Low frequencies tend to pile up in parts of the room and abandon others like a rough water day off Land’s End (except not moving). What you should be hearing is the rumble and noise coming and going as you move about the house. The effect is quite pronounced. As you slowly turn your head, the rumble character will increase and decrease and in some conditions becomes almost stereo as one ear responds a little more than the other.

Your description is not of a sound wave as much as possibly being sensitive to an electrical wave. You can have those be relatively constant through a house or building since they don’t bounce from walls or the floor. They go straight through.

Is that the case? If the effect does come and go a bit as you wander about, you should find one of the “loud” areas to put the microphone. You might also consider starting the recording and wandering a bit with the microphone. If the mic is going to pick up anything, that should do it.

I live under some serious high tension lines and there are some areas of the house that I can’t use for recording because of that. I wonder if one day I’m going to have funny looking children.

Is there any way you could attach a picture of the house? My impression of Olde English Countryside is hopelessly affected by British television. It has a thatched roof, right, and a bulldog in front?

Koz

Many thanks for the reply Koz,

Well you have identified a problem straight away and that is that I had the Chord set at 12v.

(In my defence I did a sound check (the microphone was in situ and I counted out loud to ten) when I first set it up, and this Audacity recorded. (I had also activated the Start Monitoring option by the microphone icon and could see the bars dance in the Meter Toolbar, so I made the assumption that I had set it up correctly.)

With regard “You can’t slide the equalizer controls up and down and immediately hear the effect”, I made use of the preview button after moving each slider, but as I’ve said I know not what I am doing, so cheers for clarifying that.

Your description of an electrical wave is very interesting as it is virtually coincides with that which I describe in my third paragraph, and something I have some thought of; but as there are no pylons near the house other than the main feed into the property from the pole by the side of the road, (this is running at a domestic voltage and nothing like the power those pylons can carry [I know the sound of the pylons as there is a park a few miles down the road from me and while standing underneath a pylon one can literally feel the power and hear the buzz.]), it is difficult to imagine what could cause such an electrical wave, but could something small cause an electrical wave?

Nevertheless, I have always maintained the noise is created by something that is turned on manually then left to run given the time I can hear it (nearly always at night beginning at around 00:00 then on until 08:00 give or take an hour or so each side of those times), but I have cut all the power to the house and listened out for it and on some occasions one can hear it while on other occasions I cannot, so I do not believe the source of the noise emanates from within my property.

What I think I shall do, in order to follow you guidance is to take a wander around (as far as the cable will reach), the room with the microphone; if this proves to be unsatisfactory I might buy a 20m XLR cable in order to be thorough, so I can get around the first floor.

In the meantime I have attached some screenshots of Audacity’s preferences; I would not have thought I changed a lot within any of the options available, but if I need to do something in order to facilitate the capture of this noise then please let me know.

The microphone may not die at 12v, but it wouldn’t work right, either. 12v is a standard Phantom Power specification, but it’s falling out of favor because it was always a make-do solution adopted only by a subset of makers. 48v has been the standard since the thirties and I suspect your microphone can maintain its specifications with a “sloppy” 48 volts drooping down as far as 18, but no further.

I had a similar problem with ordinary electrical interference. I listened to a radio show every Saturday and a fraction of them were trash because of what was clearly electrical buzz and hiss. No small feat this because I have a roof antenna and I can see the transmit antennas at the station.

I secured my equipment and took the whole house off the power grid which did nothing for the noise. I walked around the neighborhood with a radio and headphones trying to locate the general area. The obvious target was my high tension lines. They were a little noisy, but my noise got worse away from them and settled in the area slightly east of the house. Straight residential. My suspicion was somebody’s refrigerator was on death’s door because of the cycling times. I kept a log for a while. I called the city and they said neighborhoods as old as mine many times had bad ground/earthing leads and the whole house would electrically lift and start to radiate like an antenna.

The house next door went to an extensive renovation for sale and I haven’t heard the buzz since.

I wondered if you had done a voice test before you went to search for the problem.

I’m also interested in your comment that the problem stops dead at your exterior door. Does it? You can pass into the front yard and back several times with your eyes closed and tell exactly when you cross the threshold by the noise level?

No pix of the house?

Koz

There is a distinct rumble, similar to a distant tram or lorry, on the “No Audible LFN Clip.wav” !
(it starts about half way through the clip, drops off, then comes back in the last couple of seconds.)
I presume that this is a different sound - not the one that is causing the problem.


It is possible that the frequency may be too low for the microphone to pick up, and that you are sensing it as a “vibration” which is then interpreted in the brain as “sound” even though it may actually be below the range that can normally be heard.
Something that you could try on a mild evening when the noise is present - try opening all of the doors and windows in the property - interior doors and exterior doors. Is the sound still there?

Hello again Koz and Hello Steve,

I was looking through my emails when I first requested the council investigate this problem, and I stated then that I thought, due to the nature of the sound that it was something that could be turned on and off, hence some sort of appliance.

Therefore, Koz this could be it “The house next door went to an extensive renovation for sale and I haven’t heard the buzz since” unfortunately my neighbour has run his property into the ground and I have always suspected he doesn’t maintain the interior in any conscientious fashion, this is of course a real concern and one that I had brought to the attention of the Environmental Health officer (EHo), but it is the word of my neighbour over mine which has seen two EHo investigations stall, but the problem, rather the intrusion remains. (I’ve got a couple of pictures for you).

You might be right Koz regarding the possibility of the noise being present outside, but during the day even the low level of ambient sound drowns out the LFN, as I say, it is only at night when the house is dead still I can hear it and of course when you‘re are trying to sleep it is very difficult not to focus on sounds. I know this appears to be rather weak of me, but I can assure you that the LFN penetrates one’s mind, I have used every type of ear plug there is- foam, wax, plastic, etc. but speaking with the guy who sells them on-line, he says a LFN will penetrate most things including the various types of material earplugs are made from (this was very honest of him, as I asked before buying my first set). So yes the LFN could be present during the day, but I am in need of capturing it first; once I have done so, I could take external (to the house) recordings in order to eliminate that possibility.

I would also say that even at night when the LFN is active, it is inaudible when one goes outside, but the possibility remains.

Hello Steve- the LFN, I would describe as a continuous pulsing: possibly two or three beats a second (but given I am no audiophile, there could be ten or twenty beats per second- I know just how incredibly unhelpful that is, but what can I say).

The area I live in does have a main road (an A road not motorway, although one can view it as a B road) very nearby (40 yards away from my front door), but it is only apparent during rush hour, you get the odd lorry/ motorcycle, or car with a big exhaust pass by during the day, but I live at the top of a hill, so once the vehicle has passed the sound diminishes very quickly as it travels down into the valley (you can still hear it especially if the biker has screwed it on (so to speak) or the car has a particular powerful engine and is moving quickly through the gears, but these sounds only last a 10-20 seconds then they are gone. There are no trains nor trams and the flights paths which used to be very regular are not so regular (I used to have Concord fly over twice day before she was decommissioned, and that was something if the pilot was in a hurry), but even then the noise would only last 30-40 seconds), but with the evolution of engine design and the alternating of flight paths, the aeroplanes are hardly noticeable (I believe that no commercial flights are allowed to land at UK airports after 23:00), so at night traffic noise is not a possibility, as I say, before the LFN began three years ago, it was silent at night.

You mention vibration and this is something that Dr. Leventhall did mention (I managed to get 30 minutes on the phone with this gentleman, but he is retired now so, I was unable to persuade him to come and monitor the LFN). The opening of windows does help, it is as if the pressure of the LFN is released, but this is not practical option every night with our English weather. Nevertheless, how could I monitor vibration? So without a way to monitor vibration in addition to the possibility that the microphone cannot pick the LFN up; even with it’s range of 15hz to 20 kHz, then what do I do?

I was looking at Audacity and see it has a Spectrogram is that the same as a Spectrum analyser? I am afraid I am being rather brain-dead, but with the constant headaches and lack of sleep I know what it is to be a zombie, albeit without the appalling diet. But if I cannot actually capture the LFN with the equipment I have, in order to amplify it and play it to the EHo, then the question is trying to get some sort of data that I can present to the EHo in order for them to look once more at the problem.

Anyway I will upload a recording (48v on the Chord) made last night, the LFN was active (01:04hrs).

There are a few minor low frequency peaks, but nothing that is not also present in the “No Audible LFN Clip.wav”.
This leads me to think that the “sound” may be a vibration below 20 Hz, so not strictly speaking “sound”, but a vibration that you perceive as “sound” as it rattles your brain. This is a phenomena that has been alleged regarding low frequency vibrations generated by wind turbines, though I don’t think that it is universally accepted or scientifically proven.

Are there any wind turbines near you?

Having previously lived in the country, that does not surprise me at all. On a still night the ambient sound can be incredibly low.

This is an interesting possibility. It may not seem very likely, but (other than wind turbines) you seem to have exhausted the likely explanations. There is a possibility that the the vibration may be caused by your house. You know how you can create a tone by blowing across the top of a bottle - the larger the bottle is, the lower the note. Now imagine a bottle as big as a house - the “note” is going to be extremely low. Why does it happen sometimes and not others? That could be due to wind direction. Note that it does not need to be a strong wind - it is more likely to occur with a gentle but constant wind. Why did it not occur until 3 years ago? Are there any new nearby buildings, or buildings removed, or trees fallen down. or anything else close by that could change the air flow? Have you had new windows, doors or central heating? Does opening one particular window or door have a particularly significant effect on the sound?

If the LFN is below 15 Hz, then you will probably need a specialist infrasound microphone. Unfortunately these tend to be very expensive, though your local environmental health organization should have access to the necessary equipment. Alternatively, see if you can get help from any nearby wind farm opposition groups as they are likely to have information and contacts regarding infrasound.

pictures

No thatch. I’m crushed.

No dog, either.

How many fireplaces do you have?

Can you block the openings or close the dampers during the noise events? This from the observation that opening the windows and doors changes the effect.

That’s why I said it reminded me so much of my electrical noise problem. It wasn’t at all fuzzy or ambiguous. It was there from 1612h to 1835h and then it stopped dead for about three hours only to start up again.

Are you there or aware during the start or stop of the effect?

Is that a Land Rover back there?

Koz

There’s nothing wrong with the microphone. It is specification flat to 15Hz which means it’s still cranking much lower than that. Given what it is, it was intentionally designed to have no natural lower limits and it’s omnidirectional, further contributing to its stability and quality. It’s certainly possible that the other two devices won’t do it, particularly the Audio to USB adapter/device/cable.

Audacity, as we all know from painful experience will process “audio” down to DC battery voltage. So it has no natural lower limit at all, sometimes even when you want it to.

I don’t expect this to actually work, but if you put a pan such as a wide cookie sheet with water on the floor, can you see ripples?

Do you have a basement/cellar? Is it audible down there? Attic?

If we keep you athletic enough, you won’t have to go to the gym later.

Koz

Hello Koz, Hello Steve,

No wind turbines in the area I am afraid.

If the Audio to USB adapter/ device/ cable is the problem how else do I get the XLR cable outlet from the Chord to the iMac?

I did look at the “woodwind” effect of wind passing over the chimneys, but this I discounted as on days past when the LFN was active, there was no wind (of course, there are days when there is wind and LFN, but you can see what I have done).

In two of the rooms where one can hear the LFN there are chimney flues, but in the rear room downstairs there is no flue, but the LFN is still prominent there, so I have to discount this “woodwind effect” (not forgetting that this intrusion began some 3 years ago, but I have lived here for 25+ years, so I am used to the sound of the house and the surrounding area).

“Vibration caused by your house”, this is probably it, I believe my next door neighbour has something which he turns on and leaves, he is aware that it causes a disturbance, but is unwilling to do anything about it, but because I am unable to prove it’s existence, here I am.

If you look at the picture of his property, at the front window there is a white blob (a third of the way up on the right), this is part of his security system, I have always maintained that it is his server or computer that records the CCTV that is making the noise.

I bought a vibration app for my iPhone, http://www.dld-llc.com/Diffraction_Limited_Design_LLC/Software.html, but so far I can see nothing in it’s readout that I could show the EHo.

So if there is a way to monitor electrical items (computers, refrigerators, etc.) or the electrical waves that an electrical item emits, all from the other side of a wall, then I am all ears.

Kindly forgive the indulgence but I have to say, it is the constant headaches that are most worrying, the lack of sleep I can almost deal with, but when you take four Paracetamols (500Mg) and they do nothing, then various other concoctions of pain killers and they do nothing, you can imagine my growing concern.

As soon as I leave the house it comes as a relief, but selling is not an option.

Cheers fellas.

What’s on the other side of the neighbor?

They’re both stand-alone houses, right? They’re not, as in the US, Semi-Detached – one common wall?

I was about to say that I find it hard to believe an effect that appears in your house wouldn’t also be audible while standing between the two houses. Even if your house happens to resonate at that pulse rate, it has to be “excited” by something, and it’s not easy to move a brick house. See: Three little pigs.

It’s also rough to believe that a server computer could make enough noise to transition between two walls and a property space – if there is one. If you have one common wall, then yes, certainly. We had one computer install that was clearly audible on the other side of the wall and we had to take steps to isolate it, particularly since the other room had to record audio.

You may be stuck with specialists. I don’t know of a USB microphone amplifier with specifications down that low. The desperation method would be to contact Behringer. They might have application notes. Their web site pushes the idea of how well it records music, but nobody who has been in audio for longer than a week would use it for that. Maybe a cathedral microphone. Any time you want to record Bach in The Cathedral of Peter and Paul, you trot out this microphone. That would work, but it’s unlikely. It’s a specialist microphone and somebody must have had design notes or other information.

They may have an on-line forum.

Google.

Koz

Hello

Yep, they are semi-detached; the hedge running on the right hand side of the photo of my property denotes the boundary.

“If you have one common wall, then yes, certainly. We had one computer install that was clearly audible on the other side of the wall and we had to take steps to isolate it, particularly since the other room had to record audio.”

Cheers.

A slightly off-the wall solution: Get some tropical fish. The constant sound of the air pump will probably mask the LFN, but you will “like” the sound of the air pump because its restful humming reminds you that your beautiful fish are alive and well. (does your adjoining neighbour keep tropical fish?)

Yep, they are semi-detached

Oh, then it’s easy. Tape the microphone to the common wall. Pick a spot roughly in the middle between the sides, top and bottom of the room. The effect should be magnified several-fold with that trick. As usual, two recordings, one with and one without.

I’m going with a refrigerator or freezer compressor. My sister has an older fridge that you can clearly hear rumbling in the basement under the kitchen when it’s cooling. If you know which wall the kitchen is on, use that one.


I wonder about that aquarium thing. Have you ever seen an aquarium that didn’t have a noisy pump? They exist, you just have to clean them more often. They feature fish that are not constantly racing two and fro to get away from the pump noise. They’re a lot less entertaining. Much less action. Much more like nature.

So in order to avoid torturing the fish, you could just buy the pump and put it in a pail of water.

Koz

Just waiting on a longer cable to get the microphone up to the wall itself, then hopefully, if you are right Koz, this will capture the sound. I’ll post up the results as and when I can get them.

Cheers.

It may capture more than that. You are experiencing the sound waves after the wall has had a chance to move the air in your house. Putting the microphone on the wall should record not only that sound, but also the overtones that normally wouldn’t transmit to the air.

I still bet you find compressor or cooler noises.

Koz

Well, this is it: a recording with the microphone firmly up against the dividing wall (I’ve been waiting to get the loudest night of LFN for weeks now and tonight was the night, the sound has been carrying through the house unabated); I have to say that I can detect no difference when using the Amplify then the Low Pass Filter with this recording compared to those recordings I have made when the microphone was sitting in the middle of the room, but maybe something was captured.

Steve: I did try an iPhone app that played soothing sounds to try and cover this f&*ck!n6 LFN, but when it came down to it, it was just noise on top of noise, but I appreciate the suggestion.

Anyway, I have certainly run out of ideas (looking at the Spectrogram (if I’m reading it correctly) there is plenty of LFN between the 300 and 0 mark but this could be the case with every recording when trying to capture ambient noise, I simply do not have the experience to do something constructive with this data if it does mean something.

I did a simple amplify and analyze and there is a very significant bump at 19Hz – just below where most people’s hearing stops. It’s the majority contribution in that sound clip. Nothing else comes close. You do have a lesser 49Hz bump which I attribute to the 50Hz power in your country.

If I listen on my killer sound system cranked to high volume I can hear a pulsing throbbing sound, but it’s still not anything we can send to the housing authorities, for one thing, it’s not very loud and for another, you need a killer sound system to hear it.

[time passes]

I pulled some magic. I filtered out everything above 30Hz and then jumped the pitch of the sound up 300%. Then Amplified again. That’s the attached clip. Most houses do not rumble at 19Hz.

Koz

Now we need the control clip on a night without the rumble. Same settings so we do a direct comparison. Koz

Maybe someone was murdered and they hid the heart under your floorboards. Koz