Photosounder: editing a sonogram

    I publish this topic at the request of HammeremmaH mired in the red . I hope that with your help he will be able to publish his next article on his own.

    Have you ever thought about how great it would be to work with sound in a graphical editor?
    - Here is the violin. Where is my healing-brush, now we will smear it so that no one even notices.
    - But the vocals, see the “drunk” stripes? Come on here your eraser - make a phonogram.
    Something like this can describe the process of editing a sonogram in Photoshop.

    Photosounder- software that allows you to analyze the sound fragment, build on its basis a "canvas" of the dependences of frequency-time-volume. Moreover, this “canvas” can be exported as an image, edited, and imported back into the program, where changes in the image will be converted into sound. Sounds fantastic?



    Theory. How it works?



    To analyze and build a sonogram, the FFT algorithm (FFT - Fast Fourier Transform) is used. As a result of the FFT algorithm, the sound is decomposed into all its frequencies. Information for each frequency in each time interval is analyzed and as a result, an image is constructed where time is plotted on the X axis, frequencies are plotted on the Y axis, and the volume at the intersection of coordinates is expressed by the brightness of the pixel. This is how it looks in practice:

    image

    The program allows you to export a sonogram as a BMP image, as well as import a sonogram image back. With the help of our favorite graphic editor, we can make any changes to the sonogram, as a result of which the frequency content of the future sound will also change.

    Here is a small demo:


    And here is how this demo was done:


    What does this give us?



    With a certain level of dexterity and zeal, you can make excellent phonograms without losing the quality of the original. You can also use the effects of a graphic editor to get a completely new sound. But even more interestingly, using this technology you can slow down any sound any number of times without loss of quality and without the presence of granulation effect (which is used in almost all time-stretching algorithms). Some examples are offsite .

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