Resonant Bridge

Resonant Bridge, contact mic


Resonant Bridge, contact mic with no mass coupling to back of element

Resonant Bridge, contact mic with mass coupling to back of element

To a man with a contact mic mounted on a magnet, every sound source looks like a large lump of steel, same way as the guy with a hammer sees nothing but nails…

My luck was in when I came across this concrete footbridge across a dual carriageway. So I set up, carefully placing myself over the central reservation so drivers don’t get paranoid I’m about to zap ’em with a speed camera or throw stones or drop magnets on them. You get some funny looks attaching magnets and a piece of wire to a bridge by the other people, and the regional Police HQ is only 1/2 mile away. This unpreposessing bridge has a decent tone to it, presumably ringing to the vibration of the traffic passing by. Which was awesomely noisy – you don’t realise just how loud the tyre noise is on a road until you try and cycle a stretch like this and find your ears ringing afterwards. The contact mic worked its usual magic in getting rid of all this racket.

Resonant Bridge, traffic noise, OKMII binaurals w battery box

The two recordings with the contact mic were made, one with the mic held to the bridge with a strong magnet, the other with the same mic held to the bridge in the same way, but with an approx 0.5kg weight acting as a reaction mass on the other side of the piezo, to see if this picked up low frequencies better. You can hear the difference – or not, for yourself!

the traffic seen from the footbridge
the traffic seen from the footbridge

Piezo contact mics seem to cause a lot of pain for people losing low frequencies, but I do not feel I am short of low frequencies here, using a basic FET buffer. The peaks of the bridge resonance are 120Hz, 240Hz, 380Hz, 760Hz. There is, however, energy at 22 and 43 Hz at -36dB on the resonant peak, at a similar level to the broad peak around 3kHz which is probably the percussive sounds amplified by the piezo self resonance. The piezo was a Maplin YU87U 27mm 1.8kHz item terminated in 3.9Mohms, but the circuit could be improved to work better with a HiMD recorder mic input of 5k.

Amsterdam Rising

view from the window
view from the window

1 min bells coming in at varying times

Recorded from the roof of the Hotel Intercontinental, a few hundred yards from Amsterdam’s Centraal Station

I asked for a cheap dive close to the centre as I wanted to record a repeat of a concert from the late 1970’s which was repeated on DAB I requested a room high up, and installed a DAB tuner with a wire aerial slung out the window. Loads of signal strength, as to expected in the middle of the capital city. The concert was recorded digitally with HiMD and from the analogue output using my old MDLP as backup. The HiMD failed. Moral of the story is don’t edit your HiMDs on the deck if you want to be sure… Anyway, the backup was good.

After the concert, I stoked up with a few beers, and in the morning heard the city come alive to the sound of the bells. The first one started a good five minutes before everyone else, though the 1 minute format lops most of the overzealousness off. It’s a rotten recording, hissy as hell, even though the sound was loud enough to be easily heard through the window.

Why is there a hook sticking out of the roof, you may ask? It puzzled me too, but all was explained when I took a canal boat tour later on that day.

recorded from Sony ECM907 at 44.1kHz HiSP. High-pass filtered from 220Hz at 12dB/octave to reduce traffic noise.

recorded 19 Aug 2005

Ice Cream Van

Now here’s a sound I haven’t heard for a while – an ice cream van

The chirping of the local sparrows start off the clip, then as the van comes round the corner the kids get excited and the honky tonk sound starts

I’m not sure if this is a genuine mechanical ice cream van seriously off tune or a recording of one. It has an odd combination of honky tonk untuned notes combined with what sounds like really rough distortion at the end, but the recording is not over 0dBFS and not so close as to compress the OKMII mics

Ain’t the web a wonderful thing. Apparently these have always been electronically amplified. They used to use a Swiss musical box amplified by vacuum tubes (valves) as long ago as the 1950s. Nowadays the amplification is electronic, and, ideally, output using Grampian Horn narrowband speakers aimed at the road surface. The Swiss clockwork has long been replaced by an electronic chip to synthesise the tunes. Beats me what is wrong with a CD of the music box – you could have up to 99 different chimes that way. However, that isn’t the way it’s done. Thanks to Tom at MusicThing for the heads up

from 25 June 2006

Sparrows Chirping In The Rain

One of about twelve sparrows I saw, sounds like there were many more in the flock.
One of about twelve sparrows I saw, sounds like there were many more in the flock.


1 min continuous chirping

There’s something about rain that brings out the chirp in sparrows. I counted 12 of them, but the sound of this lot in the ivy and elder bushes sounds like a lot more. Why do sparrows all get up a chirp when it rains?

recorded from Maplin electret inserts on tree at 44.1kHz PCM  to a PC via mic preamp. High-pass filtered from 440Hz at 12dB/octave to reduce traffic noise

Women singing in Ferihegy 1



Women singing at Ferihegy

No, I don’t know why they broke into song here. However, the old Ferihegy 1 airport terminal has an air of faded grace that the more modern Ferihegy 2 just doesn’t. That is a soulless modern airport building. This is a marble-panelled cavernous space that clearly inspired this lot to sing.