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Help needed in audio conversion

Started by Unknown May 9, 2006
Hello All,



            I am currently looking for an 2 channel to 5.1 channel
audio conversion algorithm implementation, plz can anybody help in
regarding this, as there may be a set of formulas or algorithm
available.

 

Thanks a lot in advance,

With warm regards,

-Prasad B C

Prasad wrote:

> Hello All, > > > > I am currently looking for an 2 channel to 5.1 channel > audio conversion algorithm implementation, plz can anybody help in > regarding this, as there may be a set of formulas or algorithm > available.
Sure. The simplest way: Out.L = In.L Out.R = In.R Out.C = 0 Out.RL = 0 Out.RR = 0 The most complex way: Out.L = hL2L * In.L + hR2L * In.R Out.R = hL2R * In.L + hR2R * In.R Out.C = hL2C * In.L + hR2C * In.R Out.RL = hL2RL * In.L + hR2RL * In.R Out.RR = hL2RR * In.L + hR2RR * In.R where hL2L, hR2L, ..., hR2RR are a bunch of impulse responses, and * denotes convolution. Between the two methods, you can choose the one that suits your purposes / hardware / specs the best. Hint: getting the impulse responses might be a bit of a hassle. Regards, Andor
i wan to do the second one, and can you please help me or just give me
the procedure of finding the impulse response

Hi Andor,

i wan to do the second one, and can you please help me or just give me
the procedure of finding the impulse response.

Your suggestion would be of great help

Regards,
-Prasad

mailprassi@gmail.com wrote:
> i wan to do the second one, and can you please help me or just give me > the procedure of finding the impulse response
It's quite an euphemism to say it would be a hassle. If I didn't misunderstand anything, here's how it should be like Well, I can think of it in two ways, one simple, one not. The problem with the first one is that you're supposed to be able to use each element of your 5.1 system (btw Andor wasn't it a 4.1 system you described or does the "C" one counts for both a satellite and a bass?) as a microphone, and since it's unlikely that you can do that, I can only think of one suitable way to do that. First, you have to get yourself a microphone, and correct me if i'm wrong, but I think you need to know its frequency response (you can do so using a speaker and something that would be used both as a speaker and as a microphone but it would take a lengthy explanation, well ask me if you want it). Let's assume you got the impulse response matching to the mic, and call it hM Now, you need to choose a signal to use. In order to make things much simpler, use one with a linear frequency response, like a linear frequency sweep or a MLS signal. Now, play and record with your mic this signal being played through each part of the 5.1 system, deconvolve each with hM and then cross correlate each. there you got the impulse response for each part. Now convolve impulse responses together to obtain the impulse response described by Andor. Example : hL * hR = hL2R I only hope I didn't get it wrong. Anyways, I don't think it's worth the hassle, and I don't even know why you need to know the frequency response for each speaker in order to do it, if you could explain me Andor :-) Alright since I'm really bored I'll explain you how to get hM, the impulse response for your microphone. You need your microphone, one speaker, and well... i'd go for one speaker with a transformer (to amplify the sound to decent voltages when using it as a mic). We'll call the mic M, the speaker S and the speaker with a transformer T. Play your signal (a linear chirp or MLS signal) throw S, record it with M and record it with T. Then play your signal through T and record it with M. Cross correlate each obtained signal with the original signal, and what do you got? your first signal is hS * hM, the second one is hS * hT and the third one is hT * hM Since what you're looking for is hM, you need to convolve the 1st signal with the 3rd one, and deconvolve the result with the 2nd. There you got hM*hM. In order to obtain hM from that, FFT that signal, turn it into the polar form, sqrt only the magnitude bins, turn back to rectangular form, IFFT and there you should have your impulse response for your microphone.