T.J.Moir Personal pages

Auckland North Shore Hum

(C)2006 by T.J.Moir. All rights reserved.

For some time now there appears to be certain people who have sensitive hearing that can hear a low frequency humming noise late at night or in the early hours of the morning. The problem appears to be all over the North Shore of Auckland. We don't know the origin of the generic hum which appears to be world-wide.
Download and listen to the Auckland North Shore Hum in stereo.Quite a few people have said that this is what they hear (minus the cracks and pops caused by noise). I recommend that you do not listen too loud.You need lots of bass. Recommend you use headphones if possible.Note - cheap speakers built into an LCD screen or equivalent will probably not play this sound. You do need reasonable quality speakers or headphones.The actual hum sounds just like this except the level is very low making it very hard to pick up except those with good hearing. Late at night it appears to waken some people. If you get troubled here are a few suggestions...Try playing a CD of rainfall (they are available!) or similar which should mask the sound.You can try sleeping with a fan on if you don't mind the sound of the fan.Alternatively there is a link below to an entirely new method to help you sleep with the hum problem.

This is a 16 bit stereo .wav file which has not been compressed in any way. Power spectral density is the average power in the signal (for one channel here) plotted versus frequency.It is sometime known as periodogram since it is in fact a digital estimate and not a true analogue power spectrum. The power spectrum was obtained by succesive averaging over blocks of FFT (Fast-Fourier Transform) estimates.
Thank you to the following people - Dr F.Alam,Phil Strong and Ms Nair Mana Tsuji.Special thanks to all the NZ residents and overseas sufferers of the Hum who have contacted us.

Note:For the power spectral density graph as shown here and in the London Times - dB as used in Elect Engineering is a relative thing. Don't confuse the scale with standard sound pressure readings or you will think the hum is deafening! The spectrum is important in that we can see that a harmonic is so many dB down on a fundamental - it is relative and not absolute to any reference.

The map below is not complete - there are parts where there is hum not shown - Devonport,Grey Lynn,Westmere,Herne Bay.Also further north in Whangaparoa -Stanmore Bay.

Hum file recorded on Wed 15th November at 9PM Glenfield
Longer Hum file recorded on Wed 15th November at 9PM Glenfield
Power Spectral Density of Hum
Another Power Spectrum from a nearby house
Read this about dBs - important
Map showing map of some of North Shore Hum spots.

A new technique to radically reduce the effect of hum on your sleep.

These are the linear microphones I used.
This is the digital recorder I used.
The external Sound Card.

The new mixer I am going to use - low noise.

The following is an approx 3 minute recording of the hum sampled at 441Hz.(to save space on the server) Note, it is binary big-endian format.I used LabVIEW to write this file and do all the analysis.Download here (mono only).Recorded on 23.11.06 in Glenfield some 1km from the first recording.

The following matlab code will read the binary file meur.bin
  • %Read meur.bin into array x and play out speakers
  • fileid=fopen('meur.bin');
  • x=fread(fileid,'int16');
  • sound(x,441)

  • An approx 3 min MP3 stereo of the Hum in Glenfield.

    On March 23rd 2007 Brendan Clark of Howick(Auckland) recorded the following which may well also be the hum. Nobody else could hear it in his house until he recorded it. It is recorded at 16 bits 48kHz mono. Download Howick Recording.

    Latest: In mid March 2007 Nair Mana Tsuji (who has been to a great many of the houses) tested a Faraday Tent. A Faraday tent is a bit like a Faraday cage except it is portable. Look at this link (NOTE - FIREFOX does NOT work - it misses most of the page - you have to use IE) for details. Faraday Tent (single layer). This tent at 1MHz has an attenuation of 20dB going up to 60dB at 500MHz-1GHz (the mobile phone region is near 1GHz). It goes on working to about 2.5GHz. The news is that Nair could still hear the hum clearly in this tent indicating that microwaves for mobile phones and the majority of other comms systems are not to blame.eg wi-fi,bluetooth,LANs,3G etc. This would not block ordinary AM radio of course since the carrier is less than 1MHz.(or VLF for submarines). TETRA uses bewteen 380 and 395 MHz and between 410 and 425 MHz and so we can rule out TETRA once and for all. Nair reported that there was no attenuation in the hum though of course her mobile phone did not operate within the tent indicating the tent does work.

    What the hum probably isn't - some notes - far from difinitive though: