http://www.k-wave.org/forum/topic/what-is-the-cause-of-the-calculation-error-without-using-filtertimeseries Support for the k-Wave MATLAB toolbox en-US Wed, 13 May 2026 01:33:42 +0000 http://bbpress.org/?v=1.0.2 q http://www.k-wave.org/forum/search.php http://www.k-wave.org/forum/topic/what-is-the-cause-of-the-calculation-error-without-using-filtertimeseries#post-5080 Sun, 10 May 2015 20:32:04 +0000 bencox 5080@http://www.k-wave.org/forum/ <p>Hi Tim, </p> <p>An even simpler example will show this error: if you send the toneburst from a point source to a sensor some distance away you will see it. It is an instance where you can see the effect of the underlying numerical scheme that k-Wave uses. You are seeing the effect of the bandlimited interpolant inherent in the k-space pseudospectral scheme. See Fig. 2 in <a href="http://www.k-wave.org/papers/2011-Treeby-JASA.pdf">this paper</a> and the accompanying text for an explanation.</p> <p>There are two ways to ameliorate it: ramp up the signal (as you have done using filterTimeSeries) or define a larger source region with the source amplitudes weighted so that it is tapered towards the edges, eg. use a Gaussian as a source rather than a point. </p> <p>Hope that helps.<br /> Ben </p> http://www.k-wave.org/forum/topic/what-is-the-cause-of-the-calculation-error-without-using-filtertimeseries#post-5075 Fri, 08 May 2015 22:30:34 +0000 golubyatnikov_tv 5075@http://www.k-wave.org/forum/ <p>Hello, my name is Tim. Sorry for my English.</p> <p>I try to simulate the acoustic wave propogation with the signal frequency 4kHz. When I use filterTimeSeries function, I get good signal on the receiver. But without using this function I see high-frequency calculation error. </p> <p>Here is example image: <img src="http://imageshack.com/a/img903/8317/hZqxFI.png" /></p> <p>While the simulation was running, I saw:<br /> "...<br /> dt: 4.5045us, t_end: 5ms, time steps: 1111<br /> input grid size: 200 by 200 grid points (1 by 1m)<br /> maximum supported frequency: 33.3kHz<br /> expanding computational grid...<br /> computational grid size: 240 by 240 grid points<br /> ".</p> <p>The maximum supported frequency of grid (<strong>33.3kHz</strong>) is much larger than the signal frequency (<strong>4kHz</strong>). I can't understand what is the cause of this calculation error? I have not found the explanations in the documentation and on the forum.</p> <p>Here is simple code to reproduce this situation:<br /> <pre><code>% area settings gridSize = [200, 200]; cellSize = [0.005,0.005]; % [m] medium.sound_speed = 333; % [m/s] ts = [50, 100]; % tranceiver positions amplitude = 10; % [Pa] freq = 4000; emitTime = 0.001; % [s] modelingTime = 0.005; % [s] source.p_mask = zeros(gridSize); source.p_mask(ts(1),ts(2)) = 1; sensor.mask = source.p_mask; circleReflectorRadius = 12; circleReflectorPosition = [150,100]; kgrid = makeGrid(gridSize(1), cellSize(1), gridSize(2), cellSize(2)); [kgrid.t_array, dt] = makeTime(kgrid, medium.sound_speed, [], modelingTime); source.p = amplitude * toneBurst(1/dt, freq, ceil(freq*emitTime), &#39;Envelope&#39;, &#39;Rectangular&#39;, &#39;SignalLength&#39;, kgrid.Nt); %source.p = filterTimeSeries(kgrid, medium, source.p, &#39;ZeroPhase&#39;, true); disk = makeDisc(gridSize(1), gridSize(2), circleReflectorPosition(1), circleReflectorPosition(2), circleReflectorRadius); medium.density = ones(gridSize) + disk*100; % define the acoustic parameters to record sensor.record = {&#39;p&#39;}; %% prepare display parameters densityMask = medium.density - 1; dm = source.p_mask + sensor.mask + densityMask; dm(dm&gt;0) = 1; simulationParameters = {&#39;DisplayMask&#39;, dm, &#39;PMLInside&#39;, false, &#39;PlotPML&#39;, false}; % run the simulation sensor_data = kspaceFirstOrder2D(kgrid, medium, source, sensor, simulationParameters{:}); plot(kgrid.t_array, sensor_data.p);</code></pre> <p>Thank you. </p>