# CONVOLUTION??? If that is it's name...

Discussion in 'Microphones (live or studio)' started by eFe, Jan 19, 2005.

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1. ### eFeActive Member

Joined:
Jul 26, 2003
Location:
Buenos Aires, Argentina
Hi guys, at least found a really good question to ask. Please, i would like those very detailed answers and discussions about the subject.

Some time ago I started hearing and reading about this thing called "convolution". Some time later it turned to be something like the explanation to softwares like Acoustic Mirror and such, that works with audio impulses. I have some good idea of the way it works but have lots of blank spaces in the middle and i'm not sure about the real principle of the work. Neither i'm sure if this is the right forum to put the topic.

Please i would like you guys to start by explaining the main principle that it uses. Is it based on Delay? I have the idea that it is like a sum of audio that feedbacks itself. Well, i'm looking forward to the answers.

By the way, this kind of soft has given me great results for almost every aplication but I think this is to be discussed in the next topic. (Arena de otro costal).

Thank you for the patience. eFe

PS: Has anyone noticed that I can never post some short topic or reply? :roll:

2. ### David FrenchWell-Known Member

Joined:
Jun 19, 2002
Location:
Indiana
Take two waveforms, A and B. A is the waveform you wish to convolve, and B is the impulse. To convolve the two wavforms means to place a copy of A at each sample position in B, with the amplitudes of each copy of A being scaled by the amplitudes of each sample in B.

3. ### eFeActive Member

Joined:
Jul 26, 2003
Location:
Buenos Aires, Argentina
So it IS a sum of waveforms.
Now it's only has to do with amplitud?
What happens qith frequency?

4. ### David FrenchWell-Known Member

Joined:
Jun 19, 2002
Location:
Indiana
In the frequency domain, the spectrum of the output will contain only those frequencies that are shared between the two files. You are essentially filtering the spectrum of one file through the spectrum of another file, sort of like 'playing' one sound through another. Mathematically, this is a multiplication of the spectra of the two files. The so-called law of convolution states that convolution in the time domain is equal to multiplication in the frequency domain. The inverse is also true, and that operation is called ring modulation.

5. ### eFeActive Member

Joined:
Jul 26, 2003
Location:
Buenos Aires, Argentina
Thanks David, where can i find this "Law of convolution"?

6. ### David FrenchWell-Known Member

Joined:
Jun 19, 2002
Location:
Indiana
I just told it to you.

7. ### NemesysGuest

The following is a really nice free book on digital signal processing found on the Internet in pdf form.

http://

It does not mention the aforemention convolution law explictly, but you may find this interesting to read anyway for a more in depth explanation of convolution.