Home » Uncategorized » Some initial spectrograms of Zoom H4n recordings

Some initial spectrograms of Zoom H4n recordings

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In preparation for attempts to record the Hum using classic audio techniques using highly sensitive electret microphones, I made some night recordings using a Zoom H4n recorder, out of the box, while I learn to use the unit. I noticed something unusual. The two screenshots I’ve attached are from the well known and widely used Audacity software. The first recording was taken from the basement of the house, with the mains power on but no fans or motors running in the house. The bright (loud) spikes are me setting the recorder in place or moving it. The Hum, perceived by me at roughly 56.5 Hz, was very loud as I made the recording.


Screen Shot 2016-09-02 at 3.13.48 PM.png

The second recording was made from inside my car in the driveway (obviously with the ignition off and windows up). Notice the steady modulation in the lowest end of the audible range.

Screen Shot 2016-09-02 at 3.14.45 PM.png

Perhaps the most important result from this is that when I listen to the recordings, I cannot hear the Hum in them. Obviously I can’t conclude anything yet, but as I learn more and begin to master the technology, I will report on what I find.

If you are an audio expert – particularly one who can comment professionally on recording low frequency environmental sounds – feel free to post here or contact me at glen.macpherson@gmail.com


  1. Glen – that’s very interesting. I suspect it may be related to your car as a Helmholtz resonator. Recall that we discussed Helmholtz resonators (soda bottles) before (formula here):

    Your car probably has some air access even with closed windows. The car probably has a volume something like 3000 liters. Now GUESS (all you can do!) some length (lower case L) and radius R!!! I took the length as 4 cm and the radius as 1 cm. Got about 2.4 Hz. Very rough.

    Now, in the spectogram, viewed as the time events (not the frequency) we see a pulsing (you say modulation) of perhaps 1.4 Hz (14 in 10 seconds).

    This is the same general resonance responsible for that annoying throbbing you sometimes get at highway speeds with a back window slightly cracked. Same general sub-audio low frequencies.

    How would the resonator get excited? Light breeze? No good answer.

    Second test on highway?

    Do I believe this? Not really.


    • charlie says:

      If the car is acting as a Helmholtz radiator would opening or closing the windows alter its resonant frequency? If the low frequency modulation varied with window aperture then that might suggest the Helmholtz effect.


      • Charlie – I expect it would, although principally I would expect it to damp the resonance. That is, to resonate well, the excitation has to be within limits, else it dies. (You have to practice a bit with a proper bottle). I’m suggesting it is the same resonance that you sometimes get with a back window cracked perhaps 1 inch while driving 60 mph. If you have ever done this, you know what it is like “full throttle”. ( A very annoying and alarming throbbing at a few Hz, First time I did it, I stopped to see if I had a flat.) I’m suggesting the same resonance at a much lower level. The frequencies are right ballpark.

      • charlie says:

        I do know the throbbing that can occur in a car with the window open a bit. As I recall, opening or closing the car window while this was happening either stopped or started the throbbing. I have to admit that I don’t recall the actual frequency of the throbbing changing with window aperture.

        Even if the frequency cant be changed easily, perhaps just leaving the window open or the door ajar might interfere with cars resonance (ie. damp it) sufficiently to show up on the audacity readout.

        This probably a silly suggestion, but when a cars ignition is switched off some devices in the car still use a little power, eg. a clock or maybe some anti theft device etc.. Could it be possible that some electrical device in the car is responsible? The pulses on the readout are a little too fast to be a clock ticking at 1 Hz, but maybe something else is putting out a quiet but regular sound. But I don’t know how such a sound would show up on Audacity , maybe it would be quite different to what Glen’s diagram shows.


      • Charlie says:

        OK one more speculation. Maybe the regular pulse is a result of heart beat. if Glen was holding the mic, or perhaps just close to it, and it was as he mentioned a sensitive microphone, maybe it could pick up on his pulse. The frequency is in the ball park.


      • This is what I was thinking. It’ll be easy to test next time.

    • charlie says:

      Edit : That should have been Helmholtz resonator not radiator.

  2. TINMA says:

    Interesting. I hope some audio specialists lend a hand.

    I on the other hand am anticipating the arrival of fall. As I said in other threads, temperature seem to affect whether I hear the hum or not.
    I moved to this house in October last year. A quiet end of town. I was looking at this house at about this time last year and did not notice any hum. After moving in around the first week of October, shortly after I started hearing this enigma. The temps around here have stared dipping into the middle and lower 50’s. I believe it has to get to 45 degrees or less for me to hear it. I have a theory as to why, but will keep that to myself for now. i will let everyone know if I was right or wrong, just to help further this investigation into the “HUM”.

    If my investigation eliminates my HUM as being not the same as your hum, it is important to all of you. If not….well on we go.

    Good luck Glen on your experiment.

    By the way, I did friend you on facebook.

  3. George G. says:

    Two vital tests:
    a) Repeat the recording with one mic muted then compare channels
    b) If your recorder allows, disable the AGC

  4. Mary Gaylor says:

    Has this already been investigated as a possible reason why we ‘hear’ the hum…?



    • SGVH says:

      Good find, Mary. Very interesting. First article has 11 references to science/research reports or articles.

      How come nobody has ever told us we have this “Magnetite Shyte” in our brains+bodies? Do med doctors even know about this Magnetite stuff?

      Same article mentioned how bad MRI’s are due to its radiation interaction w/the Magnetite. Great. I think I’ve had 3 MRI’s in my lifetime, between approx. 1995-2005, but none recently.

      So, do Hum &/or Vibration people have MORE Magnetite than other people?

      Or, are our skulls/bones thinner? (it mentioned a calcium connection).

      Or, is it that we are merely being EXPOSED MORESO to either/&/or ELF-EMF-MWR/RF than other people? (the article mentions all 3).

      Going to read the 2nd one now.

    • Charlie says:

      That’s interesting. I only just read your comment, so I haven’t read the articles yet. But only the other day I read something in the news about high levels of magnetite in people’s brains. IIRC some researchers were investigating the possibility that there could be some correlation between high levels of magnetite and certain neurological disorders.

      I didn’t think about it in terms of the Hum. OK I’ll go read the articles now!


  5. Gerry says:

    Magnetite and Cryptochrome!

    I posted this to an earlier thread back in June (Targeted individuals etc).


    Nice to see magnetite and magnetic fields have cropped up once more!

    (Thanks Mary!)

    A smoking gun perhaps? 

    Could magnetic resonance caused by EM interference of magnetite(or cryptochrome or both!!)within human anatomy and at the point of human auditory perception, be decoded by the brain and transcribed into a tone that sounds just like….

    ….The HUMMMMMMMMM???

    Seems plausible to me!

    I’m just not sure how to go about getting the proof!!!!

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