A waveform which appears (on an oscilliscope or in a waveform editor) as a series of rectangles alternatively above and below the horizontal centerline. To qualify as a square wave, the rectangles above and below the center line must be of equal width. The harmonic analysis of the square wave reveals that, like the triangle wave, it lacks any even harmonics; however the odd harmonics (particularly the 3rd, 5th, and 7th) are much more prominent than in the triangle wave. The sound of a raw square wave has a nasally quality, somewhat like singing with one's nose pinched shut.

Note that the square wave is really just a special case of the pulse wave.

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