What is signal? What is noise?
After students have completed the semaphore activity, ask them how successful the sending and receiving of the message was. If they tested the OpAmp with various inputs, ask them to describe the sound quality emanating from the speaker. How does it compare to their car stereos? Headphones? Why is it different? The conversation should transition to an introduction of signal and noise using the PowerPoint Intro to Signal & Noise (Google Slides | PowerPoint) . To clarify the potential confusion over these common terms, students are asked to build and then refine an operational definition from examples.
Slide 2 Classroom Signal: teacher’s voice Noise: sound from all of the other students talking
Slide 3 Commodities traders Signal: buy or sell order Noise: Audible & Visual background confusion from other traders
Slide 4 Urban Astronomer Signal: Light from star Noise: light pollution
For slide 5, students should work in groups to formally write a definition of signal and noise that is shared & discussed. From the provided examples, ‘signal’ should be loosely understood as: the information of interest one is trying to observe. At this point, students’ definitions of noise will probably revolve around something interfering or coming between the signal and the receiver to make observation difficult.
Slide 6 introduces a different type of noise with a low-res webcam and a poor analog tv signal. For both devices, the noise similarly makes the signal (the visual image) difficult to observe. What is different, however, is that both of these devices are interpreting a signal and presenting it to us for observation. Rather than a third entity coming between the signal and the observer, the noise is inherent to the device itself through the grain of the low- res webcam or the poor reception of the analog tv.
Slide 7 pushes the examples to include “noise” where no signal is being transmitted such as a static-filled tv or a radio tuned between stations. Students should discuss how to alter their definition of “noise” to include devices displaying random, meaningless data or corrupting the signal with this data.
Slide 8 asks students to identify the signal and noise for motion data collected by a sonic ranger (motion detector). The signal is the position and time data with the associated calculations for velocity and acceleration, while the “noise” is the spike on the graph. This spike represents random, meaningless data interpreted by the motion detector as a position value. If students are familiar with motion detectors, they should be able to brainstorm possible causes for the noise in the data—such as another object (a hand or book) being read by the motion detector, classroom sound interfering with the detector, etc.
Slide 9 shows a zoom-in of same data collection during the initial motionless period. Students should be asked to identify the signal and noise for this section as well. The signal again is the position and time data interpreted by the motion detector. Questions to ask the students: How does this noise compare to the spike in the last example? (happens continuously, very small fluctuations in signal) How can we account for this noise? (most likely part of the device itself, not an outside interference) How does this noise impact our measurements? (limits the precision of our data, can only be confident of position data with a certain range of uncertainty) How do calculations affect this noise? (Students should be able to notice that small fluctuations in the data are exaggerated and amplified as calculations are performed for velocity and acceleration graphs).
The final slide (10) introduces the main source of noise within electronics—random electron movements related to thermal energy.