Objective: Marking labels indicating the positions of the violin bow on an acoustic signal, for example, a single musical note played by a full-length bow. The following video shows the example I am talking about, please just take a look from 1:00 to 1:03: https://www.youtube.com/watch?v=XIKPHsVyxKs
If divide the bow into three parts with equal length, roughly two markers can do it. So what I want to do is put those two markers on the corresponding acoustic signal, like this:
The objective is to figure out "oh, at this and that moments, the bow has traveled 1/3 and 2/3 of the whole length, respectively" when looking at the acoustic signal. A naive way is to simply divide the time axis of the acoustic signal by three, but it cannot be assured that the velocity of bowing is constant.
Method: According to the article http://www.ubicomp.org/ubicomp2013/adjunct/adjunct/p211.pdf which used a pair of colored SMD LEDs (as emitters on the bow) and color sensor photoresistor (as receiver on the violin) to tackle the problem. However, the circuit and the explanation of figure 3 are not clearly described, which made a lot of problems for me.
Problem: In short, based on my understanding, by installing SMD LEDs with different colors on the bow (red and blue marks in the case of the above figure), and a color sensor photoresistor on violin which detects the time-varying voltage when illuminated by SMD LEDs on the traveling bow, the objective described in the first place could be achieved. The following figure explains the idea:
So the peaks in the figure indicates the positions of both LEDs. By aligning the time-varying voltage and the acoustic signal, the objective shown in the first figure is solved.
1. Is the above statement correct, achievable or not?
2. If so, how to set the circuit on both two ends (emitters and receiver)?
I am fairly unfamiliar with hardware and electrical components, hope you can help me if possible, thank you very much!
EDIT: I've implemented the LEDs and photoresistor as detector, and it works as I desired. Here comes the other problem: the alignment of the recorded audio signal and the time-varying voltage detected by the photoresistor. What came to my mind is a acceleration-sensed LED installed on the driving point of the bow, which makes a blink at the moment the player drive the bow. The idea is to blink the LED once the change of the acceleration direction is detected by a component. Such change in acceleration direction will thus make a impulse on the displayed time-varying voltage which indicates the onset of the audio signal.
How could I achieve such acceleration detector combined with a LED, with an acceptable size to be installed on the violin bow?