# Impulse response for MID/SIDE

Hello,
sorry for that, it seems to be quite simple logic puzzle. But I wonder and can’t find the answer.
I am not good in technical terminology, so I will describe.
When you have impulse signal, like 1, 0, 0, 0… and all zeros. When you treat that signal by some EQ, and then calculate FFT, you can see what exactly EQ does with your audio signal. I suppose everyone here know what I am talking about.
So I can do the same for left and right channel. But how to do that for mid/side ? As far as I know MID is just sum of L and R. So it seems to be obvious. But SIDE is difference between both channels (L minus R). So in that case it will be zero.
Am I missing here something?

If it is zero, then you have a mono signal, i.e. no difference between left and right. But there is no problem to feed it into your algorithm, since a silent signal should be a valid case.

If it is a stereo signal, where left and right are different, you can process the side signal just as normal as any other signal.

Hope that helps

OK, for example Fabfilter Pro-Q2 (and many other plugins) have option to tweak only SIDE, but then I see no changes on my graph. How to fix it?

E.g. the code I wrote analyses the mono sum, to save CPU, also because the plugin can process any number of channels…

OYou have to send a signal which contains only side information in order to analyze what a plugin does to a side signal. When you send the same signal for left and right it is mid only. Just send an Impulse to the left channel and let the second one all Zero.

Edit: sorry I made a mistake: send a positive Impulse for the left Channel and a negative Impulse for the right! Thats side only!

OK but how to make simple impulse to be side? Or more precisely: How to make SIDE to be just impulse? That’s the question

Hey Daniel, that’s what I thing the best describe my graph

Hey danielrudrich
Thanks great, I thought about that, but then I have no MID signal

By the way: how can I link your names here, that when I mention first daniel, and danielrudrich there would be your icons or something like that?

Then do my first suggestion: an impulse only to the left. Then you have a mid AND a side signal (make sure you read those articles). That signal is in the LR domain, you feed it to a plug-in which expects LR-domain signals, converts it internally to MS, processes it and converts it back to LR domain, so it can be used as a regular stereo signal.
So you get your IRs in LR domain. If you want to see what the plugin did in MS domain you have to convert it yourself (make sure you read those articles about how to do that ).

With an @ you can tag people.

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