Category Archives: field recording

Listening from 2317km away!

This is utterly incredible!

The other evening (Saturday, Jan 15th) I was out in the garden messing around with the bath I have installed for sound FX recording, and I heard some distant booms. They sounded like large-scale fireworks or munitions, distant enough to have that “pahrump” attack to them, but carrying enough sub-bass that you could feel the scale. My first thought, why would anyone have a fireworks display during daylight? This was about 7pm and sunset isn’t until 9pm at the moment. When they have a large fireworks display in Wellington harbour, we can barely hear it here….

Soon after I went inside and a friend on Twitter messaged me:
Did I hear it?
Yes, but what was it?
The eruption in Tonga, 2500km away!

At first I thought he was joking.
But checking official NZ MetService Twitter account:





There were comments on that tweet from people all over NZ who heard it.
I would not call what I heard “a rumble” – it was definitely discrete booms!

But even more amazing: people heard it in Alaska 6000 miles away!!







Check the shockwave timelapse captured by the Himawari Satellite

“Japanese Geostationary Satellite ‘Himawari-8’ captured an eruption of a volcano near Tonga. Not only the eruption but also the shock wave can be seen. On the other hand, the terminator between daylight and night caught up with the shock wave. This means the terminator runs faster than the speed of sound, that is, the surface speed of the Earth’s rotation exceeds the speed of sound, and we are rotating at supersonic speeds!”



And there is great info here with regards to scale of eruption.

This is a recording of the eruption captured in Fiji, 800km away!

Sonic boom from Hunga Tonga Hunga Ha'apai Volcano

I posted some comments on a local FB group to see if anyone else heard it, and a dozen or more commented they did. But one was skeptical: “Are you sure? On the 6pm news it had already erupted and they had an initial video of the early tsunami waves”

Me: The speed of sound in dry air at 20 deg C = 343 m/s.
Plimmerton is 2,317km (or 2317000metres) from Tonga…
By my maths that = 6,755 seconds or 112 minutes of travel time.
(Speed of sound would vary with humidity and temperature)

I can understand their doubt, and as one of the reports mentioned,
Scientists will be studying this event for many years to come.
Meanwhile Tonga has a massive recovery ahead.

Temperature Inversion

My field recording work is often exterior, so I am often dependent on the weather…
Wind & rain ruin recordings (unless that’s what I’m recording) but checking the hourly weather forecast I keep noticing how the wind always dies down at night… Why is that?

Answer: temperature inversion
Longer answer is here

“The wind speed tends to decrease after sunset because at night the surface of the Earth cools much more rapidly than does the air above the surface. As a result of this difference in cooling ability, it doesn’t take long for the ground to become colder than the air above it. The air in close contact with the ground — say in the lowest 300 feet of the atmosphere — then becomes colder than the air above it.

This circumstance leads to the development of what is known as a temperature inversion. Inversions dramatically reduce the amount of mixing that occurs between different vertical layers of the atmosphere. As a consequence, once the inversion sets up (after sunset), it is much harder for fast-moving air above the ground to mix down to the surface, where it could appear as a gust of wind. During the day it is very easy for the air to mix and cause surface gusts.”

First Field Recordings

By 1998 I was in the slow motion process of dropping out of University – I’d started a degree in Electrical Engineering, and the further I got into it the less I liked it! One of the few interesting elements was the anechoic chamber which I spent time in when I could…

Around the same time a couple of friends were at Ilam Fine Arts School. The drummer in my band was studying film, and via him I managed to start using their field recording equipment: a beautiful Nagra 4.2 and a Sennheiser MKH416 shotgun mic in a Rycote.

Prior to going to Film School in 1990, I spent a gap year living in an abandoned church in central Christchurch, playing in bands and starting to experiment making my own music and sound. And borrowing that Nagra and 416 whenever I could!

Sometimes the greatest motivator can be a lack of access, so whenever I had that Nagra I spent quality time with it – learning to record, and also learning to manipulate sound with it. Making tape loops, playing sounds backwards and splicing tape.

At one stage I had a part time job, working a nightshift at a gas station in the suburbs. I think their motive was that my meagre pay was cheaper than insurance, while mine was being paid to do very little. Except I didn’t – I did all sorts of things while I was at work, and remember a couple of people coming into the station about 2am, only to find the counter covered in bits of 1/4″ tape!

Another part time job I had was at a company who built sound systems – I mainly helped with assembly but I made friends with a hippy guy who worked in their machine shop. He built all the speaker enclosures so had a full workshop of saws, routers, drills etc… and I soon realised this was an opportunity not to be missed!

I managed to talk him into coming in to work during the weekend, and borrowed that trusty Nagra and 416 again and recorded a great little library of machine tools. One of my favourite sounds from that session was an air powered staple gun, I was recording at 15ips as much so i could slow sounds down as for the quality. And that staple gun sounded great at half speed.

I think those recordings would be the earliest recordings that are still in my library. At some point in the 90s I transferred them to DAT, at real speed and at half speed. And then a few years later digitised the DAT and added it to my growing CDROM sound library… and then as hard drives became affordable, copied the CDROMs to hard drive, and now to a NAS.

So here is a few of my earliest recordings, time travelling from 1988 to your ears now!

Kia Ora

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