Overview.
In this assignment, you will write a program to create a music visualizer using the
MinMax algorithm.
A music visualizer generates graphical effects that move and change in sync with audio playback,
adding life, color, and energy to the music.
The MinMax algorithm is a widely used method for creating such visualizations
and is used by platforms such as
SoundCloud,
Spotify, and
ffpmeg.
Digital audio.
We represent digital audio (such as streaming music) as a sequence of n
real numbers between –1 and +1.
Each value corresponds to the amplitude of the sound at a specific moment in time.
We refer to the entire sequence of values as an audio signal and
to each individual value as an audio sample.
MinMax algorithm.
The MinMax algorithm divides the audio signal into k groups
and associates a real number (between 0 and 1) with each group.
These k numbers are plotted as vertical bars. Here's how the
process works:
Treat the n audio samples as being divided into k groups of equal length.
Each group contains successive samples, starting at sample 0.
For each group i :
Let \(y_i\) denote the largest absolute value of any sample in that group.
Plot a vertical bar from \((i, \, -y_i)\) to \((i, \, y_i)\).
The height of each vertical bar corresponds to the maximum
amplitude of the audio samples in that group.
Taller bars represent louder sections of the music.
This visualization captures the dynamic intensity of the music over time.
MinMax example.
Here is a tiny example with n = 12 samples and k = 3 groups.
Each group contains 4 samples.
In this example, n is a multiple of k,
so each group contains exactly n / k samples.
If n is not a multiple of k, each group contains
\(\lfloor n \, / \, k \rfloor\) samples.
For simplicity, we will ignore any leftover samples.
Your program.
Write a program MusicVisualizer.java that takes two command-line arguments
(the name of an audio file and an integer k for the number of groups)
and produces a music visualizer using the MinMax algorithm,
as described above.
Additionally, as you process each audio sample in group i,
play it so that the visualization is synchronized with the audio playback.
Set the canvas size to a wide aspect ratio, such as 1000-by-100,
for effective visualization.
Input and output libraries.
This assignment relies upon libraries from real-time audio playback and graphics.
In our course, we use the open-source libraries
StdAudio
and
StdDraw.
FAQ.
Why draw the vertical bars symmetrically above and below the x-axis?
It's just a visual style choice. Some visualizer plot in only one direction,
from \((i, 0)\) to \((i, y_i)\) instead of from
from \((i, -y_i)\) to \((i, y_i)\).
Why is the visualization choppy when k is very large?
Drawing on the screen is CPU intensive.
If k = n, the program would attempt to redraw the visualization
44,100 times per second, exceeding most LCD monitor's refresh rate (typically 60Hz).
Why is explicit synchronization between graphics and audio not needed?
The StdAudio library is configured to play 44,100 samples per second,
ensuring automatic synchronization.
Are there other music visualization algorithms?
Yes. Another popular one is the Root Mean Square (RMS) algorithm.
Instead of computing the maximum absolute value within a group,
it computes the square root of the sum of the squares of the audio samples.
