Compress (stretch) a given fixed-frequency squarewave along the time axis, resulting in an increase (decrease) of frequency. The design presented here is meant especially for a really smáll change: “the pitch is núdged” - in an analog way. This can find application in music synthesizers / keyboards. This circuit does nudge in the positive or negative direction (just like the Doppler effect) – by simply swapping two connections in the circuit.

please refer to the attachment - thanks!