Measurement of the resonance curve (Acoustics)

[Jens Noriʇzsɔɥ]

A simple fix apparently is 1 –> 2 in

Code:

        <if less="true" equal="true" greater="false">
            <input as="a" clear="false">run</input>
            <input as="b" type="value">2</input>
            <input as="true" clear="false">fft2500</input>
            <input as="false" clear="false">FFTaverage</input>
            <output as="result">FFTaverage</output>
        </if>

However, the number of runs is off by two then. I am a bit unsure how to properly fix it as the analysis block is run like

1. on initialisation, before tapping play,
   
2. after tapping play, without audio data,
   
3. and higher: “regular” runs are starting
   

[Jens Noriʇzsɔɥ]

The “cycle” attribute looks like a quick fix. A proper solution would be checking the buffer length if there is sufficient data for a first run…

[solid]

Dear Jens,
I just have found this problem. A new version has to be published where this bag is corrected.

[solid]

Hi,
I have added the following before the block shown by Jens and it works:

<!-- 2023 -->
<count>
            <input as="buffer" clear="false">fft2500</input>
            <output as="count">count</output>
</count>
        <if less="true" equal="true" greater="false">
            <input as="a" clear="false">count</input>
            <input as="b" type="value">0</input>
            <input as="true" type="value">0</input>
            <input as="false" clear="false">run</input>
            <output as="result">run</output>
        </if>
So run remains zero until appearance of fft2500...

Example is a tube of 23 cm length with open ends.

Best
Mikhail

[Jens Noriʇzsɔɥ]

Hm… I still obtain “Runs 1” before I tap play, both on Android and iOS. Is this on purpose?

[solid]

I am also surprised where it comes from...

[J_Almer]

Dear @solid,

thank you for the wonderful experiment. I tried as acoustic resonator and it worked perfectly. Both, the sweep option and the FFT.
Then i thought, this could be wonderful for High-/Lowpassfilter with RC. I built one with C=100nF and R=1000Ω.
I can measure the damping (see attached) figure with an oscilloscope, but didn't suceeded with an audio option.
My idea was to use a 3.5 mm 4-conductor and use and audio chanel R and the microphone pin AUX.
But no success. Sometimes it was misinterpreted by the phone as signal to reduce the volume.

Have anyone an idea?

[solid]

Dear J-Almer,

maybe your smartphone is too modern, it is better to use old models for this experiment. Your proposition worked perfectly well. I have chosen  R = 10 kOhm and C = 0.1 µF for the characteristic frequency 1/RC = 1 kHz.