Impulse Response
Add an Impulse Response subnode () to a 1D plot group to create an impulse response plot. After defining the characteristics of the impulse response, click Plot () to create the impulse response plot. Add a Color Expression or Energy Decay subnode as needed. The impulse response plot reconstructs the impulse response based on a Ray Acoustics simulation.
For details on setting up a Ray Acoustics model and postprocess the impulse response, see Impulse Response and Receiver in the Acoustics Module User’s Guide.
Go to Common Results Node Settings for links to information about these sections: Title and Coloring and Style.
Data
From the Dataset list, choose an applicable dataset or None. The default option, From parent, uses the dataset from the parent plot group node. Only the Receiver 2D and Receiver 3D datasets are valid for this specialized plot.
From the Frequency interpretation list, choose an interpretation of the frequency: Octave (the default), 1/3 octave, or 1/6 octave. This selections should coincide with the frequency interpretation used in boundary conditions and sources in the underlying Ray Acoustics simulation. The frequency content and resolution of the impulse response are based on this selection.
Expressions
Set up the variables that are necessary for reconstructing the impulse response. In practice these variables are used to define and add the contribution of each ray that intersects the receiver dataset to the impulse response.
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Define the frequency variable for the rays (SI unit: Hz) in the Frequency field. The default is rac.f.
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Define the power variable for the rays (SI unit: kg·m2/s2) in the Power field. The default is rac.Q.
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Define the density (SI unit: kg/m3) in the Density field. The default is rac.rho.
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Define the speed of sound (SI unit: m/s) in the Speed of sound field. The default is rac.c
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Define the number of reflections (SI unit: 1) in the Number of reflections field. The default is rac.Nrefl.
For all text fields, click the Replace Expression () button to select a predefined quantity and replace the entire contents of the field.
x-Axis Data
From the Transformation list, choose a transformation of the data on the x-axis: None (the default) for no transformation, or Discrete Fourier transform. If you select to display a discrete Fourier transform (DFT), choose one of the following options from the Show list:
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 Real part, to show the real part of the output only.
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 Imaginary part, to show the imaginary part of the output only.
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 Amplitude, to show the amplitude of the output (the default).
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 Phase, to show the phase of the output.
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 Frequency spectrum, to display the function’s frequency spectrum by computing the number of frequencies and the frequency range based on the FFT (fast Fourier transform) of the function. The transform is valid for all functions, but what you get corresponds to a periodic continuation of the function outside the chosen bounds. To specify these values manually, select the Number of frequencies check box and enter a value in the associated field (the default is based on the number of time samples). From the Scale list, choose None (the default), Multiply by sampling point, or Divide by number of frequencies. You can choose to scale with the sampling period to show Fourier transform values instead of a pure DFT transform. Select the Scale check box to scale the values on the y-axis so that their magnitude reflects the magnitude of the original signal. The values then have the same unit as the input data for the FFT. For a pure sinusoid, the scaled value is the peak magnitude divided by the square root of 2 (). Select the Frequency range check box and then enter the bounds of the frequency range in the Minimum and Maximum fields (in Hz). The FFT algorithm uses resampling based on linear interpolation. The x-axis shows the frequency (in Hz). By default, the y-axis shows the unscaled Fourier coefficients.
If you have selected Amplitude or Frequency spectrum, you can select the In dB check box to present the values in dB. From the dB type list, choose 10log (the default) or 20log. The display in dB requires a reference value. From the dB reference list, choose Maximum (the default) to use the maximum value as the reference, or choose Manual to enter a suitable reference value in the Reference value field.
If you have selected Real part, Imaginary part, Amplitude or Phase, the following additional settings are available: To specify this value manually, select the Number of uniform samples check box and enter a value in the associated field. If desired, select the Inverse transform check box to use an inverse DFT. Select the Mask DC check box to set the DC value (zero frequency component) to zero (not available if Inverse transform is selected). The Ignore last sample check box is selected by default to not include the last sample in the transform (not available if Inverse transform is selected). The Shift zero frequency and Scale with sampling period check boxes are selected by default. Clear one or more of these check boxes if you want to exclude those steps.
Smoothing
In this section, only available if you have selected Discrete Fourier transform from the Transformation list above, you can add a moving average when analyzing an impulse response plot in ray acoustics. To do so, select the Moving average check box. You can then choose Linear (the default) or 1/n octave from the Type list to choose the type of moving average. For the latter option, also specify n as a positive integer (default value: 1).
Advanced
The following settings are available to control the filter kernel used when reconstructing the impulse response. Each ray contributes with a power, arrival time, and frequency content to the time-domain signal.
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Define a sampling frequency fs (SI unit: Hz). The default is 44100.
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Define a zero padding length Np (SI unit: 1). The default is 11025.
Select to Remove noncausal signal (not selected per default). This options removes the unphysical parts of the impulse response signal that appear before the arrival time of the first ray. This part is generated due to the nature of the window functions used for the signal reconstruction.
Select Use fully randomized phase (not selected per default) to switch the impulse response generation to the legacy method where a random phase is applied to all rays. In contrast, the default method bases the phase on the number of reflections. The default method leads to consistent values for the direct sound.
Select Show the filters to see the filter kernels used. If the x-Axis Data section is set to the Frequency spectrum options the filters can be visualized in the frequency domain.
Select the Filter kernel as either the Brick-wall with Kaiser window (the default) or User defined. For the first option enter the Ripple factor δ (SI unit: Hz). The default is 0.05. For User defined enter an expression for the kernel expression using the definitions in the Parameters table. The default sets up the Brick-wall with Kaiser window filter.
Legends
The Show legends check box is selected by default to display the plotted expressions to the right of the plot. In plots where each line represents a certain time value, eigenvalue, or parameter value, these values are also displayed.
When Automatic is selected from the Legends list (the default), select or clear the Description, Expression, and Unit check boxes to control what to include in the automatic legends (by default it includes the description only). You can also add a prefix or a suffix to the automatic legend text in the Prefix and Suffix fields. If Manual is selected from the Legends list, enter your own legend text into the table. If Evaluated is selected, you can use the eval function to create an evaluated legend text in the Legend field that include evaluated global expressions such as global parameters used in sweeps. For the numerical evaluation, you can control the precision in the Precision field (default: 3).