IR "How to" And Technical Information

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Jay Mitchell

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Before asking questions in this forum about IRs (e.g., how to find/create/upload/change user location, etc.), please read the following:

http://axefxwiki.guitarlogic.org/index. ... r_Cabinets
http://guitarlogic.org/index.php?action=tpmod;dl=0

The above links contain the answers to most of your questions.

Edit: due to apparently widespread misunderstanding of the significance of the impulse response, I'm posting the following overview.

In characterizing the behavior of a certain class ("Linear Time Invariant," or LTI) of system - electronic, mechanical, and/or hydraulic - known as two-port (i.e., input and output) systems, a family of mathematical models has been developed over roughly the past two centuries. In one scheme, the systems were represented by families of differential equations that are functions of the time "t." In that system, there is an excitation function known as the Dirac Delta function . This function, also known as an impulse, has the property that, if the response of an LTI system to it is known, the response of the system to any function of time may be derived via an integration process known as convolution.

There are other ways of characterizing the system response characteristic. One of the more familiar ones is to transform the mathematics into the frequency domain via either a Fourier or Laplace transform. The advantage of doing this is that, in the frequency domain, the operations of integration and differentiation in the time domain are transformed respectively into division and multiplication in the frequency domain. The complete frequency-domain system descriptor is known as its transfer function. The characteristic that is commonly called "frequency response" (more technically, amplitude response) is one part of the transfer function. The other part is called the phase response. Both parts must be present for the system to be completely described in the frequency domain.

Here's the important part: The system transfer function is the Laplace transform of the impulse response, and vice versa. If you know one, you automatically know the other. They are just two different ways of describing the exact same information.

The practical offshoot of this is that, to get the impulse response of a speaker, you can use an excitation signal other than an actual impulse, and then mathematically derive the impulse response from the response to the chosen signal. If you know the frequency-domain transfer function, you can get the impulse response by applying an inverse Laplace transform (or inverse Fourier transform) to the data.

This is all by way of saying that a speaker IR is one way of encoding the speaker's characteristic response function, and that the impulse response can be accurately determined without ever sending an actual impulse through the speaker. Hopefully this overview will clear up some of the misunderstanding.
 
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