Back at Uni I was studying audio pipelines and signal processing and I stumbled across a text file written by someone at a university somewhere. It outlined how the BBC achieved the "voice" of the Daleks. It's quite simple really, you talk into a microphone, which is attached to a box. Inside the box is a signal generator that "opens and closes" a gate 30 times a second. When the "gate" is open, the sound from the microphone gets through. When the gate's closed, the sound is cut off (or multiplied by the 'gate wave'. This is called a Ring Modulator.
So, I set about creating one in Unix C. I downloaded some .AU raw audio files, and tried it out. It worked! So, I recorded some speech on my Sound Blaster Pro 2 at home, took it into Uni and Dalek'ed myself, much to the amusement of everyone else in the lab.
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So, I was raking through all my old Uni stuff, and came across the old notes I wrote about it. I fired up Visual Studio and remade it in C# for Windows.
I also realised that Star Wars droids use a similar system using a higher pitch than 30Hz and a different waveform, but same basic principle. So, I added a few options. I sent it to a few friends to play with, and forgot about it.
You can do similar stuff in Audacity, but it's not obvious. This a nice simple tool that just takes in a sound wave and spits out a ring-modulated sound wave. The sound file has to be sensible (no esoteric formats), so only .WAV is supported.