How to get audio input signal intensity at given frequency?

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Hi,
I'm looking for some way how to get signal intensity at given frequency from audio input every second. I found waveIn functions but I have no idea how to get these parameters.

Thank you

Posted 23-Apr-14 8:49am

Meldir

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Sergey Alexandrovich Kryukov 23-Apr-14 16:20pm

What's on input? What's the problem?
—SA

Meldir 24-Apr-14 9:51am

On input will be signal from VLF receiver, I need to catch frequency from 15kHz to 40kHz. Intensity is from -80 to -20dB. I need to make some function that returns signal intensity at given frequency in real time.

Sergey Alexandrovich Kryukov 24-Apr-14 11:58am

Thank you for clarification.
—SA

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**Zoltán Zörgő** · Accepted Answer · 2014-04-23T10:06:00

Solution 1

What you need is called spectrum analysis. The mathematical background is called Fourier transformation, which can't be implemented directly on a finite machine, but has many restricted implementations, like DFT and FFT. I suppose FFT is the keyword you are looking for. See this explanation: http://www.altdevblogaday.com/2011/05/17/understanding-the-fourier-transform/[^]

You could use NAudio[^] if you would use c# for example.

For MFC check these:
Fast Fourier transform using DX11[^]
http://blogs.msdn.com/b/nativeconcurrency/archive/2011/11/15/fast-fourier-transforms-fft-on-the-gpu.aspx?Redirected=true[^]

But first of all, this one: FFT of waveIn audio signals[^]

Posted 23-Apr-14 10:06am

Zoltán Zörgő

Comments

Sergey Alexandrovich Kryukov 23-Apr-14 16:21pm

Good answer, only a bit premature; it would be better to wait for the OP's explanation on what's on input. Anyway, a 5.
—SA

Meldir 24-Apr-14 9:35am

On input will be signal from VLF receiver, I need to catch frequency from 15kHz to 40kHz. Intensity is from -80 to -20dB. I need to make some function that returns signal intensity at given frequency in real time.

Bernhard Hiller 24-Apr-14 3:58am

My 5. But I fear that OP does not understand how to receive samples from WaveIn...

Meldir 24-Apr-14 9:37am

You are right, I found that it has some buffer but I have no idea how access it's data.