Measurement of the resonance curve (Acoustics)

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I have slightly modified the program after version 3 obtained by Julien in order to have "infinite" measurements (now version 4). So, I measured not only an isolated resonance of the Helmholtz resonator (100 ml Erlenmeyer flask) studied at the beginning, but also a PVC tube closed at one end which gives a series 1:3:5 harmonics corresponding to the standing waves. I obtained the expected peaks (see the screen capture) but their heights were growing ruffly proportional to the frequency. I wonder if this is not an artifact of the signal treatment in the phyphox program. In the attached figure I have divided the signal by frequency (upper panel is the acoustic response of the Helmholtz resonator and lower panel is the corrected response of the tube)... Evidently the 1/f correction can be introduced to the acquisition program, but it has to be first understood (the phyphox program was developed from the given examples).