The Sound of Sorting - "Audibilization" and Visualization of Sorting Algorithms
Sorting algorithms are an essential chapter in undergraduate computer
science education. Due to their easy to explain nature and fairly
straight-forward analysis, this set of algorithms offers a convenient
introduction to the methods and techniques of theoretical computer science and
algorithm analysis.
This source archive presents my own demo program for sortings algorithms,
called “The Sound of Sorting”, which both visualizes the algorithms
internals and their operations, and generates sound effects from the values
being compared.
The demo is implemented using the cross-platform toolkits wxWidgets and
SDL, can be executed on Windows, Linux and Mac, and runs in real time.
There are many resources on the Internet about sorting algorithms, among them
are Wikipedia, animated sorting algorithms by
David R. Martin and various Java applets by many college or university staff.
The current source package and some binaries can be downloaded from
http://panthema.net/2013/sound-of-sorting/
Some YouTube videos are also linked on above webpage.
The program and code is published under the GNU General Public License v3
(GPL), which can also be found in the file COPYING. A few of the sorting
algorithms’ implementations were written by other authors and may have
different licenses.
The Sound of Sorting demo program is very intuitive to use. It contains many
sorting algorithms, which are selectable via the list box on the right. For the
quick sort variants the pivot rule can be selected separately.
When pressing “Run”, the algorithm is started on selected input. “Step” will
stop a running algorithm, or start a new one, and halt it after performing one
operation. With “Reset” a running algorithm is stopped, and a new random input
is created. When “Sound” is activated, the program will generate sound effects
on the default audio output. The “Speed” slider changes the algorithms
execution speed by adding a delay for each array access.
Due to the 1ms resolution of timers on Windows, the speed scale is
smaller. The Linux version has a higher time resoltion < 1ms!
The algorithm’s visualization contains mostly white bars representing the value
of the array position corresponding to the x-axis. When the algorithm gets or
sets an array item, the white bar runs red for one algorithmic step. A swap
operation is represented by two bars turning red and their values being
exchanged. Some algorithms specially colorize bars which represent indexes,
pointers or other information about the internal mechanisms of the algorithm.
Both value comparisons and array accesses are counted and shown in real time.
The comparison counter includes ternary comparisons as just one operation. Due
to algorithms often using extra memory or local variables, the array access
counter highly depends on the actual algorithm implementation.
The generated sound effects depend on the values being compared. Only
comparisons yield sound output (except for in radix/bucket sort)! The length of
each comparison’s sound effect can be modified using the “Sound Sustain”
slider. The frequency of the sound is calculated from the compared values. The
sound wave itself is triangular and modulated with an ADSR envelope. This
yields the “8-bit game tune” feeling. An item value is scaled (with double
precision) to the frequency range 120 Hz - 1,212 Hz, which is large but not too
high to be annoying.
The demo program uses the wxWidgets toolkit for cross-platform dialogs and
painting. For sound output, the audio component of the cross-platform SDL
library is used.
All sources resides in src/. The main window’s GUI functions are grouped in
WMain.h/cpp. The sorting visualization, including the instrumented array
class and painting methods are in WSortView.h/cpp.
SortAlgo.h/cpp contains all sorting algorithms. These were mainly modified to
operate on a WSortView object, which exposes most of the usual array
operators such as operator[], and many special functions to create nicer
visualizations. Most notable among these, are a special swap() function and
mark() to colorize bars. There is also watch() to do live tracking of
indexes stored as local variables (use this with care)!
Comparison counting and sound effects are signaled by the operators of
ArrayItem, which is the item class of the instrumented array WSortView. As
such, all comparisons of the sorting algorithms will be intercepted by this
class.
On each comparison, the values are used to generate sound. All sound generating
methods are in SortSound.cpp. The main class here is an Oscillator, which
generates an enveloped triangular waveform of a specific frequency. Oscillators
are mixed together for the output sound. The output volume is scaled
automatically depending on the number of oscillators active.
For (somewhat) rapid development with wxWidgets, the wxGlade dialog generator
tool is use. The public version of the Sound of Sorting contains no recording
facilities. If you want to contribute a sorting algorithm, please notify me.
Written 2013-05-22 by Timo Bingmann