Does anyone know of a method that has been used to convert EEG signals into sound in the human hearing spectrum? I think it would be fascinating to be able to literally "hear" the oscillations of the brain, and it also might be possible — with some training and practice — to use this for a form of neurofeedback, or even for getting an interesting qualitative perception of one's brain state.
To do this I guess one would need to increase the frequency by around 10x, which would make audible EEG signals between 2 and 200 Hz, according to the standard description of the human hearing range as 20 Hz – 20 kHz.
A crude method might be to take a short sample (say, 1 second), duplicate it 10 times and then downsample to compress the signal horizontally. This would probably produce some nasty artifacts, but perhaps there would be a way to smooth the transitions to avoid producing discontinuous signal.
Has this been done before? Is there some accepted way to increase the frequency of a signal with minimum distortion? Any suggestions or references appreciated!