The visual feedback sounds very much like the strobe feature on my guitar tuner. I think the first like this was the Stroboconn in the 1930s.
The visual feedback sounds very much like the strobe feature on my guitar tuner. I think the first like this was the Stroboconn in the 1930s.
Peterson is the most known for their strobe tuners I believe. There are nowadays many other desktop and smartphone apps and pedals that have a strobe mode, but some are real strobes and some are only simulated. As far as I can tell, a real strobe will recreate the effect based on comparing the input signal frequency to a generated reference. A fake one will just use the estimated frequency (done by a pitch detection algorithm usually based on FFT) but instead of a needle offset or LED meter it will show a steady moving pattern, but it's not as responsive or as reliable as the real thing.
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.
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.
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.
This visual feedback is very similar. It also shows octave changes i.e if the pitch detected is 0.5x, 1x or 2x the reference freq / note set.