Musical Synthesis 101
1.3 The Oscilloscope
Authors Note: Not all of this information is necessary in order to gain an understanding of musical synthesis. I just really like oscilloscopes so I wanted to make a page on them.
What is an Oscilloscope? An oscilloscope is a tool that is used to monitor an incoming signal by visualizing the amplitude. Typically, this is done by plotting amplitude in respect to time. A heartbeat monitor is a type of oscilloscope that you have likely seen before. While oscilloscopes are used in many different fields, it also plays an important role in music production and sound design. Many synthesizers have an oscilloscope built into their display for this reason. One of the oscilloscopes benefits is its ability to visualize the shape of the audio signal in relation to its frequency. Essentially by matching the frequency of a waveform with the window size of an oscilloscope, you can cause the wave to appear frozen in time. This allows for closer examination of the waveform in order to determine its characteristics.
Analog oscilloscopes (like the one pictured above) use cathode ray tubes (CRTs) similar to those that are use in analog televisions. A cathode ray tube is a vacuum tube containing an electron emitter which is responsible for creating an electron beam that is bent using deflecting coils. The resulting display is caused by the beam interacting with the phosphorescent screen. The first CRT oscilloscope was invented by Karl Ferdinand Braun in 1897.
Some oscilloscopes have an X-Y mode which allows for two inputs to be displayed together by mapping the X and Y axis to the first and second inputs. This type of oscilloscope is known as a vector monitor or a vectorscope. More is written about the ways that audio is visualized on my page about audio visualization.
Other oscilloscopes are dual trace meaning they can display two inputs independently of one another. This can be useful because it allows the user to easily differentiate the two signals and compare and contrast them. Specifically in audio, the left and right channels are used for dual trace oscilloscopes.
Another interesting thing that happens with multiple sine waves is something called phase interaction. When two sine waves interreact with each other they can either enhance or diminish one another based on the phase of the signal. When the sine waves are in phase, meaning they overlap, they enhance each other. When they are out of phase, they diminish each other.