Exporting impulse responses

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In signal processing, the impulse response, or impulse response function (IRF), of a dynamic system is its output when presented with a brief input signal, called an impulse. More generally, an impulse response refers to the reaction of any dynamic system in response to some external change. In both cases, the impulse response describes the reaction of the system as a function of time (or possibly as a function of some other independent variable that parameterizes the dynamic behavior of the system).

For example, the dynamic system might be a planetary system in orbit around a star; the external influence in this case might be another massive object arriving from elsewhere in the galaxy; the impulse response is the change in the motion of the planetary system caused by interaction with the new object.

In all these cases, the 'dynamic system' and its 'impulse response' may refer to actual physical objects, or to a mathematical system of equations describing these objects.

Recording impulse responses

OpenPSTD Impulse Response visualised in the Blender interface

In order for impulse responses to be recorded, listener objects has to be added to the scene in before starting a new simulation. The locations of the receivers are not bound to exact points on the grid but can be placed anywhere within the domain boundaries. By means of spectral interpolation the pressure distribution at the grid points is used to calculate the pressure as it varies over time at the location of a listener object.

With a listener object selected its impulse response can be visualised in the timeline area of the Blender interface when the simulation is running or afterwards.

Saving impulse responses

Save file dialog to specify the output format

In the header of the timeline area a button can be used to write the generated impulse response to a file.

Impulse response formats

  • A PCM 16bit normalised .wav file
  • A platform dependent floating point raw file
Importing the raw impulse response in Audacity
The different ranges for raw and normalised data in the Audacity interface