Measuring Stored Energy (software)
Hi, what software can do stored energy measurements? I'm using a soundcard-based setup and I'm looking to generate the kind of graphs that S. Linkwitz used to evaluate linear distortion. I'm not interested in the 3D cumulative spectral decay graphs that are difficult to read. I want to do those 2D graphs.
To clarify I'm looking to measure the Energy-Time curves like these:
Can praxis without an audpod do it? I don't want to get an audpod.
Didn't realize you were looking for freeware. I'm not sure, but if you look through the Liberty Instruments site they probably have a clear explanation on what can be sone with the free version.
Did you try ETF?
All these do ETF (Energy Time Frequency) plots:
SIA SmaartLive 5
SIA Smaart Acoustic Tools
Plenty there to be going on with. Some or more suitable than other's BTW. I have them all but really like WinMLS, ETF and Sample Champion.
Here it goes, for 1Khz tone burst as an example (PP: means Post-Processing):
- start praxis
- open foam.px2 on primary plot
- PP: source = Primary Plot, Target = Create new graph, "Re-map to new frequencies" FFT format, sample rate = 48k, #of freq points = 16385 pts, which creates plot2
- PP: source = Plot2, Target = Plot2, "Filter" (Target to 0db), Gain =0 , delay removed = 0
- PP: source = Plot2, Target = Plot2, "Inverse FFT"
- PP: source = Plot2, Target = Plot2, "FFT" PostProc FFT size = 32768, No window
- PP: source = Plot2, Target = Plot2, "Hilbert Transform"
- Plot2->Save File Name = FlatFR (keep this around for later use, all the above steps were just to
create a flat FR file, which will be used as the starting point to create the shaped tone burst signals)
Now Doing a 1Khz shaped burst tone :
- Open FlatFR file on Primary plot.
- PP: source = Primary Plot, Target = Plot2, "Filter" Band-Pass, Frequency1 = 999.0233hz, Frequency2 = 1000.47hz, Filter Shape = Brick wall
- PP: source = Plot2, Target = Create new graph, "Inverse FFT"
on the newly creted graph, click the bolting image at the lower left corner, then click "Format" menu, and then on the time tab
double click on the word "Start" and then double click on the word "Stop", and verify that you have the
same amplitude of a single sine wave all the way through time. If it is not, it means at the filter
step above you have included more than one sine wave, if so go back to the above step and play with
the frequency regions so that only one frequency is included. You can find the frequency intervals by
putting a marker on Plot2 and make its value 1000Hz. Then going down and up with small interval
thumbwheel buttons on the marker find which frequencies are used in the graph. Note that with FFT format,
the frequencies are exact multiples of (sampling frequency/(FFT length))
- On Plot3, at time tab, select as start = 0 sec, and stop = 7msec, then click on windowing tab,
click on the "start at" white box, cursor changes to selection, on the graph click on somewhere around
750usec where the curve crosses x axis at 0. Then click on the "Stop at" white box, and click on
somewhere around 4.782msecs, which is the eight zero crossing after our start selection. This gives
a window of 4 cycles of 1Khz sine wave
- PP: source = Plot 3, Target = plot2, "FFT" PostProc FFT size = 32768, Window = Hamming (or Blackman-Harris, or whatever you like)
- PP: source = Plot2, Target = plot3, "Inverse FFT"
Now on plot3, you have the 4 cycle shapes tone burst of 1Khz in time domain. Save plot3 as 1KhzShapedTone for later use.
Now load your Frequency Response measurement which includes phase as well to Praxis, assuming
you have it on an Ascii file that is in a format importable by Praxis. To do so, on Primary Plot, select
file->open from menu. Change the file type to "general ascii FreqResp *.*" at the dialog box, choose
your file to import and do the import. The next step is important to make the imported file work
with the post processing features
- PP: source = Primary Plot, Target = Plot2, , "Re-map to new frequencies" FFT format, sample rate = 48k, #of freq points = 16385 pts
- PP: source = Plot2, Target = Primary Plot, "Inverse FFT"
you have your impulse response on Primary Plot, and the shaped burst on Plot 3 at this moment,
all is left is to do convolution and then ETC
- PP: source = Primary Plot, Target = Plot3, "Time Domain Math" Convolve Source Target
- PP: source = Plot3, Target = Primary Plot, "ETC"
Primary Plot has the ETC you were asking. You can do an ETC on the 1KhzShapedTone file and save the
result, and then compare the two by displaying the two on the same plot, by using the multi and cfg multi
tabs on the plot format.
Wow thanks guys! You guys are the best.
To be honest however, that type of measurement isn't the most usefull. Even cumulative spectrum decays are not that usefull and are merely another way of looking at a frequency response curve.
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