0.6 Jbs2020-square wave sound  (Page 2/7)

An audio graph of a square wave

I explained the concept of an audio graph in the earlier module titled Jbs2000-What is Sound? but I will explain it again here for your convenience. (Click AudioGraphSquareWave to hear an audio representation of the graph of a square wave.)

This audio graph file contains an 8-second melody consisting of 32 uniformly spaced pulses at different frequencies. The frequencies (pitches) of the pulses are centered on middle-C (261.63 Hz) . The frequency deviation from middle-C versus time is based on a square wave function with a frequency of0.5 Hz.

Points on graph

Each pulse represents one point on a graph of the square wave. Pulses with frequencies at or above middle-C are delivered to the left speaker. Pulses withfrequencies below middle-C are delivered to the right speaker.

The audio output can be thought of as an audio representation of a graph of a square wave. Pulses with frequencies above middle-C represent points on thepositive lobe of the square wave. Increasing pitch represents increasing amplitude on the graph of the square wave.

Pulses with frequencies below middle-C can be thought of as representing points on the negative lobe of the square wave. In this case, decreasing pitchrepresents points on the square wave that are further from the horizontal axis in the negative direction.

Pulses with a frequency of middle-C can be thought of as representing points on the horizontal axis with a value of zero but there are no points on thehorizontal axis for a square wave.

Four complete cycles of the 0.5 Hz square wave are represented by the 32 pulses in the 8-second melody.

Hopefully, by listening to this audio file, you can get an idea of the shape of a square wave.

Discussion and sample code

This program requires the following five classes:

• AudioFormatParameters01 (see Listing 7 )
• AudioPlayOrFile01 (see Listing 8 )
• AudioSignalGenerator02 (see Listing 9 )
• MusicComposer05 (see Listing 10 )
• SquareWave (see Listing 11 )

Three classes are unchanged

I won't bore you by repeating the discussion from earlier modules. The first three classes in the above list are completely unchanged from the module titled Jbs2010-Your First Sound Program . Therefore, I won't discuss them furtherin this module.

The class named MusicComposer05

The class named MusicComposer05 differs from the previous version only in the following respects:

• Changes in the explanatory comments.
• Replacement of the term WhiteNoise with the term SquareWave .
• Replacement of the term whiteNoise with the term squareWave .

Therefore, I also won't discuss this class further in this module.

The class named SquareWave

A complete listing of the class named SquareWave is provided in Listing 11 . I will break this class down and explain it in fragments.

Beginning of the class named SquareWave

The sound that you heard when you listened to the audio file named SquareWave was produced by the getMelody method of the SquareWave class. The SquareWave class begins in Listing 1 and the getMelody method begins in Listing 2 .

The code in Listing 1 differs from the corresponding WhiteNoise code from the earlier module only with respect to the name of the class.Therefore, I won't discuss it further.