Like all semi-trendy electronic music nerds, I became obsessed with the BBC Radiophonic Workshop, Delia Derbyshire, the Putney, the Delaware, and all that good stuff back around the turn of the century. At one point, my coworker Tim Stilson fired up Cool Edit 2000 (state of the art waveform editor at the time) and looked at the Dr. Who theme in the spectrogram view. The spectrogram confirmed what we had suspected: the echos at the end of the theme were shifting upwards in pitch.

I soon found out that these shifting echos were the product of a frequency shifter with a tape echo in its feedback loop. Apparently this combination was a popular effect in Delia Derbyshire’s toolkit, and was used most notably to create the electronic scream that was played before the end credits:

The following description is from Mark Ayres’ most excellent history of the Doctor Who theme:

The sound consists of two elements, a rising bubbling sound and a descending scream effect. First of all, let’s deal with the rising bubbling sound. The process used to create this was very simple. The first couple of notes of the closing titles (as the theme melody enters) were copied onto a new piece of audio tape. This was leadered, then flipped over so that it played backwards. The output of the tape deck was then fed into a frequency shifter set for a downwards shift at a short delay, and fed back into itself. When the tape was played into the shifter, it came out the other end milliseconds later with its pitch shifted down slightly. This output was fed back to the input and so on, creating a downwards cascade of ever more distorted sound. This was copied onto a new tape, and when this piece of tape was in turn flipped over, Delia was left with a rising flood of sound starting very distorted and slowly resolving into the opening couple of notes – this was then spliced onto the beginning of the theme.

The downwards scream was created in similar fashion. The source sound is a downwards-sliding hard-edged tone produced using an audio oscillator. Again, this was fed into the pitch shifter with very short delay, a downwards shift, and heavy feedback. Aliasing distortion within the shifter added to the overall effect. The result was mixed with the rising echoes to give the sound we are all familiar with.

I have been working on recreating these sounds with my VST frequency shifter / echo plugin, with some degrees of success. The overdrive in my analog echo simulator sounds a bit soft, but the harsh edged “scream” is also dependent on having a more edgy tone being fed into it. The process would be easier if I exposed tone controls for the internal filters, so I think that will be my next step. I find myself enjoying the sounds that the plugin makes on its own, without emulating any particular existing sounds. However, the Dr. Who sounds are so archetypal, it would be good to have a tool that can make similar sounds, so I will keep working towards that.

UPDATE, April 2016: Since writing the above in 2009, I have released an “official” plugin that incorporates analog echo and a frequency shifter in a feedback loop, ValhallaFreqEcho. It’s free, so go ahead and download it!