Explain me a VI please !!! please... low notes.....

[Guylene]

Hello !
fisrt of all , excuse my bad english (i'm french)

i really need help to explain (interpret) this project:
http://lionbob.free.fr/labview/

u can see the 2 screen shots i took :
http://lionbob.free.fr/labview/Labview1.jpg
http://lionbob.free.fr/labview/Labview2.jpg

please open the VI : http://lionbob.free.fr/labview/guylene%20&%20kendy.vi
start and use the song :
http://lionbob.free.fr/labview/The%20Microsoft%20Sound.wav
Then the sound is restored WITHOUT the ACUTE (or shrill?!) ones, I want to
keep low notes .(hard to explain me.....do you understand ?? i hope..)

The job : explain this project, this VI
but i'm a real new born with labview (-9hours of lessons)

please can you explain me step-by-step ??

a
nd someaone can explain how the Complex Fast Fourier Transform works please
?
i've never see that in Mathematics...

i'll be very happy ! thank you !

ps: i'm student, at university, and i begin with labview.

and.....i'm late but.....HAPPY NEW YEARR !

[Alberto]

Hi Guylene,

your vi does one main thing: from an original wave extract a selectable portion of its spectrum and plays the extracted wave showing the spectral analysis of both the original and the exctracted wave.

I'll try to explain the main steps:

- It opens a .wav file and extract its 8-bit sound array and normalizes it to 127 (from -127 to 127)
- Calculates the FFT and display the real part on a graph
- Creates a pulse pattern with selectable start point and length
- Uses thi pulse pattern to multiply the FFT array, thus extracting only the part corresponding to the pulse window (duration) created
- Displays the extracted FFT and plays it

If you want to play low freq. sounds simply set the retard (delay) control value to zero.


You can have
full details of the Complex FFT by opening the LV Show Context Help window and click on the function icon.


Let me know if you need more help.

Happy new year too,

Alberto

[Guylene]

Hello Alberto 🙂

thank you for your answer !

can you just just explain me the normalization to 127 ?
why 127 ? what's that ?

i think i've understand the others steps.
but i must explain this VI in 2 pages...hard...i'll try...

thank u

"alberto" a ecrit dans le message de news:
5065000000050000003E560000-1007855737000@exchange.ni.com...
> Hi Guylene,
>
> your vi does one main thing: from an original wave extract a
> selectable portion of its spectrum and plays the extracted wave
> showing the spectral analysis of both the original and the exctracted
> wave.
>
> I'll try to explain the main steps:
>
> - It opens a .wav file and extract its 8-bit sound array and
> normalizes it to 127 (from -127 to 127)
> - Calculates the FFT and display the r
eal part on a graph
> - Creates a pulse pattern with selectable start point and length
> - Uses thi pulse pattern to multiply the FFT array, thus extracting
> only the part corresponding to the pulse window (duration) created
> - Displays the extracted FFT and plays it
>
> If you want to play low freq. sounds simply set the retard (delay)
> control value to zero.
>
>
> You can have full details of the Complex FFT by opening the LV Show
> Context Help window and click on the function icon.
>
>
> Let me know if you need more help.
>
> Happy new year too,
>
> Alberto

[Alberto]

Hi Guylene,

sorry I didn't reply before, but I've been away from this site for other tasks.
In your vi the sound wave extracted is an array in 8bit format; this means that each value in the array may have a value included between 0 and 255 (8bit), this is the un-signed format (only positive numbers).
Obviuosly a sound wave array has both positive and negative values, to exctract them you have to subtract 127 from your unsigned 8 bit array.
In this way the numbers from 0 to 126 are negative, 127 is 0; from 128 to 255 are positive.
I attach a simple vi that shows these differences.

Good luck,

Alberto