# Re: How one can demonstrate that microphone is a nonlinear device?

The standard way to analyze instantaneous nonlinearities is to do a distortion product analysis.

If the nonlinearity is only slight (e.g. well below clipping), the input signal is usually either a sine wave A*cos(w_1*t) or a combination of two sine waves A*cos(w_1*t) +B*cos(w_2*t+phi), and the output is analyzed for components not at these frequencies (in particular at n*w_1, n*w_2,
m*w_1+n*w_2 or m*w_1-n*w_2, where m and n are integers).  The results can give a lot of information about the nature of the nonlinearity.

A basic reference (old) is http://www.hpmemory.org/an/pdf/an_150-11.pdf.

Harvey

At 16:43 12-06-12, ita katz wrote:

Generally for a linear system, if you apply a gain to the input you expect to get the output amplified with the same gain. In other words if for input x the output is y, then in a linear system for input g*x the output is g*y, for every choice of g. So one option is to play the same sound at various levels, record it with the mic, and analyze the recorded signal to see if the above rule holds. Of course you have to make sure, as much as possible, that every other part of the recording chain (including the source of the input signal) is a linear system by itself.

On Mon, Jun 11, 2012 at 9:13 PM, Hafiz Malik <hafiz.malik@xxxxxxxxx> wrote:
Hi Every 1,

Microphone is generally modeled using a second-order nonlinear function, that is, y(n) = ax(n) + b x(n)^{2} where x(n) is the microphone input.

How can one demonstrate this non-linearity?