Numerix Host Library .wav file read / write functions updated

New functions have been added to the Numerix Host Library to include new .wav file read/write functions from C/C++ programs.

Here is a summary of the .WAV file header format :

    4 bytes     "RIFF"      ID for a RIFF file
    4 bytes     xxxx        Length of waveform (Bytes)
    8 bytes     "WAVEfmt "  ID for a .WAV file
    4 bytes     xxxx        Size of format section (Bytes)
    2 bytes     xx          Format - "1" indicates PCM data
    2 bytes     xx          Number of channels
    4 bytes     xxxx        Sample rate (Hz)
    4 bytes     xxxx        Data rate (Bytes per second)
    2 bytes     xx          Bytes per sample (rounded up)
    2 bytes     xx          Bits per sample
    /additional informaiton that may be used in more complex wave files/
    4 bytes     "data"      ID for data section
    4 bytes     xxxx        Length of data section (Bytes)

The .wav file functions allow reading and writing of .wav files from standard C/C++ programs and includes full source code.

The library can be downloaded from : http://numerix-dsp.com/files/.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.
Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2018 Delta Numerix

Gnuplot/C On A Mac

I recently updated my Mac to Big Sur and found the previous Gnuplot (http://gnuplot.info/) installation procedure using Homebrew is no longer the best method so I've updated this blog post.

First install Gnuplot on Big Sur:

If you have MacPorts (https://www.macports.org/) installed then update it:

    sudo port -v selfupdate

If you do not have MacPorts installed then you can install it by opening the following URL:

    https://github.com/macports/macports-base/releases/download/v2.7.1/MacPorts-2.7.1-11-BigSur.pkg

Install gnuplot using MacPorts:

    sudo port install gnuplot +wxwidgets

(I like the wxwidgets API)

Perfect, lets test gnuplot :

$ gnuplot
gnuplot> plot sin(x)

We should now see a nice little sinusoid graph.

Now let's build Gnuplot/C :
$ cd gnuplot_c/src/
$ make -f makefile.macos

Now let's test Gnuplot/C :
$ cd gnuplot_c/examples/
$ ./br.sh LinesAndPoints

We should now see the graphs plotted.

Note, if you see the following message:

sh: /dev/nul: Permission denied

Then you need to do the following:
$ sudo mknod /dev/nul c 1 3
$ sudo chmod 666 /dev/nul

Now let's test Gnuplot/C again:
$ ./br.sh LinesAndPoints

Excellent. All running nicely :-)

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.
Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix

Some Thoughts On Benchmarking Applications On A Pentium PC (Windows/Mac/Linux)

The ability to benchmark DSP algorithms to check that they execute in real time is a key part of the DSP development process. I've written several blog posts on the subject including :

http://blog.numerix-dsp.com/2013/01/how-to-benchmark-some-c-code-or.html
http://blog.numerix-dsp.com/2015/01/timing-code-running-on-xmos-xcore.html

While benchmarking code to run on a traditional DSP or embedded microcontroller is a relatively simple task, due to the deterministic nature of DSP architectures, doing the same on a Pentium PC is quite tricky. I've recently tried two of the most common techniques for benchmarking DSP algorithms on a Pentium PC. The two techniques are :

    Reading the Pentium Time Stamp Counter Register : http://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc
    Instruction counting using GDB : http://stackoverflow.com/questions/21628002/counting-machine-instructions-using-gdb

The Time Stamp Counter option has a lot of disadvantages when used in a multi-tasking OS due to the whole task switching happening in parallel with the application.
The inital overhead calculation may take longer, due to a task switch, so the final benchmark may take less than 0 cycles when subtracting the overhead of calling the timer functions.

The GDB solution counts instructions but does not allow for pipelining, caching, and run-time parallel instruction execution.

So far the only option I have come up with is to use a statistical analysis of the results to get an approximation to how efficient an algorithm is.

Here are some results from some different filter functions that I have benchmarked (more details in an upcoming post about the different filtering functions).

The TSC technique shows that runtime parallelization of code gives better than 1 instruction per cycle execution but each mode was executed a twenty times and the average result was taken so take note of the problems listed above.

MODE    GDB         TSC
1              2514          975
2              1171          754
3              1188          547

In summary, GDB instruction counting gives a good approximation to how efficient an algorithm is but the Time Stamp Counter solution gives a better estimate to the actual number of CPU clock cycles are required.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.

Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix

Gnuplot/C Update II

A new version of Gnuplot/C has been uploaded to SourceForge that includes polar plotting capabiliites : https://sourceforge.net/projects/gnuplotc/.

This adds logarithmic x-axis support to the existing plot types.

Here is an image showing the capabilities :

The DTMF tones were generated using the SigLib DSP library.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.

Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix

Gnuplot/C Update

A new version of Gnuplot/C has been uploaded to SourceForge that includes polar plotting capabiliites : https://sourceforge.net/projects/gnuplotc/.

This adds to the existing plot types :
    Line Plot
    XY Plot
    Pole-Zero Plot
    Spectrogram Plot
    Image Plot

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.

Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix

Polar plot in Gnuplot

I was recently playing with microphone array polar diversity responses and did a search for suitable Gnuplot polar plot solutions. There are a number that turned up but none of them really matched my requirement so here it is :

set polar
set angle degree
set size ratio 1
set tmargin 3
set bmargin 3
set title "Microphone Polar Diversity Response : Mic Spacing 0.1 (meters)"
set key out vert nobox

set style line 1 lc rgb 'gray80' lt -1
set grid polar ls 1

unset border
unset xtics
unset ytics

f_maxGain=0.                                    # Maximum gain - MUST BE FLOATING POINT
minGain=-80                                     # Minimum gain - MUST BE INTEGER
tickstep = 10                                   # Ticks every 10 dB
numticks = 8                                    # numticks = r / tickstep :: Don't use divide because numticks is used in for loop and doesn't work
f_numticks = 8.                                 # Floating point numticks


set rrange [minGain:0]
set rtics tickstep format '' scale 0

set label '0°' center at first 0, first -minGain*1.05
set label '90°' right at first -minGain*1.05, 0
set label '180°' center at first 0, first minGain*1.05
set label '270°' left at first minGain*1.05, 0

set for [i=.1:numticks] label at first minGain*0.001, first minGain*((i/f_numticks) + 0.007) sprintf("%d dB", minGain+(i*10))
unset raxis

plot "250.dat" u (-$1+90.):($2-f_maxGain) t "250 Hz" w lines lc rgb "magenta", \
      "500.dat" u (-$1+90.):($2-f_maxGain) t "500 Hz" w lines lc rgb "red", \
      "1000.dat" u (-$1+90.):($2-f_maxGain) t "1000 Hz" w lines lc rgb "blue", \
      "2000.dat" u (-$1+90.):($2-f_maxGain) t "2000 Hz" w lines lc rgb "cyan", \
      "4000.dat" u (-$1+90.):($2-f_maxGain) t "4000 Hz" w lines lc rgb "orange"

print "Hit <CR> to continue ..."
pause -1

The data was generated in a C program and written to the .dat files, then I just used gnuplot on the command line to execute the script and plot the results.

The data files look like this (i.e. two columns : angle and gain) :

# Antenna Beam Pattern
# Angle Gain
-9.00e+01 -1.17e+00
-8.90e+01 -1.17e+00
-8.80e+01 -1.17e+00

.

.

Here is the plot for 100 mm mic spacing :

The gnuplot script allows the min and max gain values to be changed.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.

Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix

DSP Tech Brief : FIR Filter Design Notes

When designing an FIR filter it is handy to know how many coefficients are required for your desired implementation.

The Kaiser approximation is the algorithm that tells you how many coefficients your filter will need but not what those coefficients are. It is accurate when using an approximation design algorithm such as the Parks-McClellan (Remez exchange) algorithm.

For designing filters with the windowing functions there are no direct equivalents to Kaiser's approximation, it is more that you have to look at the characteristics of your signal requirements and compare them to the capabilities of the windowing functions. Note : filters designed using windowing functions will typically be longer than those designed using Parks-McClellan.

SigLib includes a range of windows based filter design functions. At the present time it does not include a version of the Parks-McClellan algorithm because there are so many already available. I had a customer recently use this : http://www.iowahills.com/Example%20Code/NewParksMcClellan.txt.

I haven't used this myself but I have heard good reports.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.

Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

Copyright © 2017 Delta Numerix