Mysterious night-time pulsing sound

Over the last few months, I’ve occasionally heard a strange sound coming in through my open window at night. It’s a distant electronic pulsing sound which comes and goes on the wind. It seems to be coming from the north of Edinburgh around Leith. It’s quiet, but distinct. I decided to record it. The resulting recording is a bit shoddy, but it does the job.

Leith Night Pulse

I’ve no real idea what could be making this sound. Any suggestions would be welcome. It sounds to me like an alarm or an alert, like it has been designed to sound as it does. I tend to hear it around 1-3 am. Given the direction it’s coming from, it could be something happening on Leith docks or something going on at the nearby sewage works. It might even be something happening on the large cargo ships and oil tankers which often sit out in the Firth of Forth. I live maybe a mile from the coast; the way it drifts on the wind suggests that the sound source is quite far off.

Some technical details about the recording

This was a bit of a hard one because the pulsing sound was very quiet and I wanted to document it to make it clearly audible. So the approach I took was to focus on and magnify the pulsing sound at the expense of an accurate recording of the general ambience.

As it was so late at night, the ambient sound level was pretty low anyway. To get a decent level, I had to turn up the gain on my Sound Devices 702 to maximum. To reduce the effect of noise from my flat and the building, I stuck the mic (my Rode NT4 in a Rycote full modular windshield) out of the kitchen window on a fully-extended mic stand. A boom pole would have been better but I didn’t have one. I turned off the freezer in the kitchen as with the gain so high the mic was picking up a lot of the hum from that. The hum was probably louder than the pulsing sound itself. I tried to stay completely still – with the gain so high, even the tiniest sounds could be picked up. Even though I was careful, there are lots of extraneous noises in there. Little floorboard creaks, doors closing elsewhere in the building.

Annoyingly, after a few minutes the battery on my 702 died and I had neither my spare battery nor the power supply to hand. I switched to a Tascam DR100 recorder, but the preamps on that aren’t as good.

Afterwards, working with the SD702 recording, it was very quiet so I normalised it. This made the pulse louder but of course also brought up the level of all the stuff I didn’t want as well, like bass rumble and hiss. So I then did some pretty strong EQ work to remove noise at the low and high ends of the frequency spectrum. I also slightly boosted the main frequency of the pulse to bring it out of the mix a bit more. The process was very rough and ready and not at all audiophile really, but it got the result I wanted: the pulse is now clearly audible, whereas insitu it was very quiet, only just detectable over the background noise.

If this sound keeps happening, I might try a few more recordings on still nights, hopefully with a bit more care and preparation..

46 Replies to “Mysterious night-time pulsing sound”

  1. I’m actually up at 3:08, listening to the incessant humm. I’m on the Cape Peninsula in Cape Town, RSA. Initially thought it was the ocean waves but it’s more electronic. Lived here all my life so the sound is not an old sound from long ago. Reasonably recent, maybe a decade or less. I’m a habitual insomniac so I would know.

  2. Heard this noise last night at 05:15 a strange pulsating almost musical sound coming through open bedroom window – hard to describe – sounded manufactured other ‘worldly’ – was a bit disconcerting seemed to be carried on the wind and lasted for about 10 minutes – I’m from Wiltshire area of uk.

  3. every couple of nights, myself and my sibling (who shares a room with me) both hear this low almost vibrating sounding pulse, similar to a heart beat. As of right now it is 11:35pm 14th June 2021. This sound has lasted around 7-8 minutes now and is irritating us both quite a bit. This doesn’t happen every night, but it happens enough for us to recognize it almost every time it happens. Anyone know the cause?

  4. i heard this last night at around 1-2am while checking on my dog barking, it was coming from over the back fence. I’d describe it as a horse galloping on 2 legs or a loud heartbeat. i went back inside and went to bed so i font know when it stopped.

  5. Columbus oh 3;40 am pulsing sound for hours. Its outside. Have decible meter on my phone that pics it up. Weird!

  6. I’m really late to this one. I’m out here in California Jurupa Valley. First time I’ve ever heard this pulsing sound. All the animals in the area lit up. Coyotes, neighbors dogs. Birds. Everything. It sounded like it was in the air. Like a heartbeat but it stops, then it goes on again. Started around 1250am ish – 105 am ish.

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