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Delia’s Tatty Green Lampshade

by Phil Taylor

One of Delia Derbyshire’s most loved natural sounds was the bell-like chime of a metal lampshade when it was struck with a soft-faced hammer. She described it as, “My most beautiful sound at the time was a tatty green BBC lampshade. It was the wrong colour, but it had a beautiful ringing sound to it.”. The sound is rich in overtones and proved to be a significant resource for sound sculpting. A Fast Fourier Transform (FFT) frequency analysis of the lampshade is shown below. The FFT is based on 2048 data points, sampled at 44.1KHz and a Hanning weighting is used. Levels are referenced to 775mV.

By removing the initial percussive attack portion of the lampshade being struck, slowing down, fading-up and applying filtering to the recording Derbyshire was able to emphasise its sonorous mystique to create a haunting atmosphere. This can be heard towards the beginning of ‘Blue Veils and Golden Sands’ where she evokes an auditory image of a relentless sun beating down on a nomadic tribe as they wind their way across a desert wilderness in the shimmering heat.

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Derbyshire also claims to have made a frequency analysis of the lampshade and synthesised it using the Radiophonic Workshop’s 12 Jason signal generators. “I analysed the sound into all of its partials and frequencies, and took the 12 strongest, and reconstructed the sound on the workshop’s famous 12 oscillators to give a whooshing sound. So the camels rode off into the sunset with my voice in their hooves and a green lampshade on their backs.”. At this time (early 1960s) the frequency analysis instrumentation available to her at the Workshop would have been primitive – she would have probably used a swept filter and oscillscope. A laborious process, however she left Cambridge with an MA in Mathematics and Music – don’t doubt she was geeky enough to have tackled it. Below is short video clip of the strongest 12 partials of the lampshade synthesised with 12 pure sine wave oscillators using DASYLab virtual instrumentation software.

It was mathematician Joseph Fourier, whilst experimenting on heat transfer work, who first proposed that any periodic signal could be reconstructed from a series of pure sinewaves of different frequencies and this little experiment does confirm his idea. However, although the timbre of the ringing in the synthesis is pretty much identical to that of the recording of the real lampshade, the synthesis is pretty ‘flat’ sounding as there is no amplitude variation and decay envelope. As time passes the ringing is changing as vibrational energy sloshes around in the metal shade and gradually dissipating. The higher partials decay at a more rapid rate than the fundamental and the relative levels of partials are constantly varying in repsect to each other – its a complex sound that shimmers and ripples with a life of its own. The synthesis is merely a snapshot of a frozen moment in time – it’s no wonder it sounds so one dimensional in comparison to the real sound. It takes a great deal of work to sculpt the bland tones of synthesised pure sine, sawtooth and square waves into something that is musically interesting enough to be useful in a composition. Derbyshire would add effects such as tube amplifier and tape saturation distortion, tape wow (vibrato), phasing, filtering, reverb and delay to breathe life into her sounds.

The lampshade used in these recordings is a ‘Coolicon’ utility lighting shade, British Patent No 419602, Registered Design No 777912. The actual lampshade that Delia used at the Radiophonic Workshop to make the sounds for ‘Blue Veils and Golden Sands’ is currently on display at the Science Museum in London.