[v15w]

The visual feedback uses time period (of ref note) and number of cycles to set the scale of waveform display. It doesn't depend on detected pitch.

I think strobe tuner's used neat analog electronics based reference and filters to visualise.

[dsego]

A few years ago I made a small tuner that mimicked the strobe effect by resampling the signal with interpolation to match the wave period (similar to an untriggered oscilloscope) and applying an IIR bandpass filter to get a clean sinewave, then showing the sinewave as a color gradient instead of an oscilloscope view. I tried a few different variations but couldn't figure out how to control the speed (sensitivity) of the movement and make it independent of the input frequency/period (apart from showing more or fewer periods in the pattern) and also it required a strong biquad filter to remove harmonics that would bleed into the strobe pattern (a similar effect can be seen in the turbo tuner (*) guitar pedal that uses LEDs to show a spinning pattern and sometimes the pattern smears or flickers), but this introduced unwanted lag. Here is a screen recording of my old app: https://youtu.be/IjYv1fDEopY

(*) I'm not affiliated in any way, I was just researching this a lot.

[v15w]

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.