Interesting. It took time for us to get the waveform stability working. We also have a smoothed wave overlay on top of raw signal. This is more a filtered version of input signal. Tried adding more filtering to get the sine wave output. But, it was too much CPU intensive. We also tried adding few overlays to this stable waveform. They did not work well and hence removed them. I agree, there is no good way to make the speed independent of input frequency. The plucked note pitch variation in flat bridge instruments like South Indian Veena is too wide when compared to pointed bridge instruments. We are planning to add additional cue that shows if a note is in tune based on pitch variation midpoint. This might help tuning the string or setting the frets relatively accurate.