# Time Domain¶

With the files in the folder SFS_time_domain you can simulate snapshots in time of an impulse originating from your WFS or NFC-HOA system.

In the following we will create a snapshot in time after 200 samples for a broadband virtual point source placed at (0 2 0) m for 2.5D NFC-HOA.

conf = SFS_config;
conf.dimension = '2.5D';
conf.plot.useplot = true;
% sound_field_imp_nfchoa(X,Y,Z,xs,src,t,conf)
[p,x,y,z,x0] = sound_field_imp_nfchoa([-2 2],[-2 2],0,[0 2 0],'ps',200,conf);
%print_png('img/sound_field_imp_nfchoa_25d.png');


Fig. 17 Sound pressure of a broadband impulse point source synthesized by 2.5D NFC-HOA. The point source is placed at (0,2,0) m and the time snapshot is shown 200 samples after the first secondary source was active.

The output can also be plotted in dB by setting conf.plot.usedb = true;. In this case the default color map is changed and a color bar is plotted in the figure. For none dB plots no color bar is shown in the plots. In these cases the color coding goes always from -1 to 1, with clipping of larger values.

conf.plot.usedb = true;
plot_sound_field(p,[-2 2],[-2 2],0,x0,conf);
%print_png('img/sound_field_imp_nfchoa_25d_dB.png');


Fig. 18 Sound pressure in decibel of the same broadband impulse point source as in the figure above.

You could change the color map yourself doing the following before the plot command.

conf.plot.colormap = 'jet'; % Matlab rainbow color map


If you want to simulate more than one virtual source, it is a good idea to set the starting time of your simulation to start with the activity of your virtual source and not with the secondary sources, which is the default behavior. You can change this by setting conf.t0 = 'source'.

conf.plot.useplot = false;
conf.t0 = 'source';
t_40cm = round(0.4/conf.c*conf.fs); % in samples
[p_ps,~,~,~,x0_ps] = ...
sound_field_imp_wfs([-2 2],[-2 2],0,[1.9 0 0],'ps',20+t_40cm,conf);
[p_pw,~,~,~,x0_pw] = ...
sound_field_imp_wfs([-2 2],[-2 2],0,[1 -2 0],'pw',20-t_40cm,conf);
[p_fs,~,~,~,x0_fs] = ...
sound_field_imp_wfs([-2 2],[-2 2],0,[0 -1 0 0 1 0],'fs',20,conf);
plot_sound_field(p_ps+p_pw+p_fs,[-2 2],[-2 2],0,[x0_ps; x0_pw; x0_fs],conf)
hold;
scatter(0,0,'kx');   % origin of plane wave
scatter(1.9,0,'ko'); % point source
scatter(0,-1,'ko');  % focused source
hold off;
%print_png('sound_field_imp_multiple_sources_dB.png');


Fig. 19 Sound pressure in decibel of a boradband impulse plane wave, point source, and focused source synthesized all by 2.5D WFS. The plane wave is traveling into the direction (1,-2,0) and shown 31 samples before it starting point at (0,0,0). The point source is placed at (1.9,0,0) m and shown 71 samples after its start. The focused source is placed at (0,-1,0) m and shown 20 samples after its start.