I want to show a graph for a song .I'm wondering which characteristic value is batter to distinguish, amplitude or frequency?

the code i am referring to:

/**
* This sketch demonstrates how to play a file with Minim using an AudioPlayer. <br />
* It's also a good example of how to draw the waveform of the audio.
*/

import ddf.minim.*;

Minim minim;
AudioPlayer player;

void setup()
{
size(512, 200, P3D);

// we pass this to Minim so that it can load files from the data directory
minim = new Minim(this);

// loadFile will look in all the same places as loadImage does.
// this means you can find files that are in the data folder and the
// sketch folder. you can also pass an absolute path, or a URL.
player = minim.loadFile("marcus_kellis_theme.mp3");

// play the file
player.play();
}

void draw()
{
background(0);
stroke(255);

// draw the waveforms
// the values returned by left.get() and right.get() will be between -1 and 1,
// so we need to scale them up to see the waveform
// note that if the file is MONO, left.get() and right.get() will return the same value
for(int i = 0; i < player.bufferSize() - 1; i++)
{
float x1 = map( i, 0, player.bufferSize(), 0, width );
float x2 = map( i+1, 0, player.bufferSize(), 0, width );
line( x1, 50 + player.left.get(i)*50, x2, 50 + player.left.get(i+1)*50 );
line( x1, 150 + player.right.get(i)*50, x2, 150 + player.right.get(i+1)*50 );
}
}

Can function_get(i) get the 1024( bufferSize() ) values in real time?
And other example is used toArray( ),can you explain that function in detail？and the difference between them?

Thank you very much.