Mindset Learn: Loudness and Pitch
This 9-minute video uses an oscilloscope to demonstrate how the loudness of a sound is related to its wave amplitude and how pitch is related to frequency. The author explicitly clarifies a concept that is commonly misunderstood: although the wave pattern produced by the oscilloscope looks like a transverse wave, sound is NOT transverse-it is longitudinal. The instrument detects compressions (high pressure areas) and rarefactions (low pressure areas) in the longitudinal wave and translates them into an electrical signal to produce a graph of Distance Vs. Time. The video then explains how the human ear functions to hear different specific frequencies of sound, which we perceive as varying pitches. Very well crafted video -- would be a good candidate for a flipped lesson.
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Bethea Medical Media: How The Larynx Produces Sound
This 3-minute animation shows the anatomical structure of the larynx, the muscles that control movement of the human vocal cord system, and explores how those muscles move to produce high or low pitches. No narration -- animation and text only.
Physics Girl: Perfect Pitch and Physics
What is perfect pitch (or absolute pitch)? This 8-minute video from Physics Girl Diana Cowern explores the concept through three musicians who demonstrate their own mastery of perfect pitch and how timbre affects this phenomenon. Note "Timbre" is one of the vocabulary words in the main lesson of this Digi Kit. It refers to the tone quality of a sound, which differs from one instrument to another.
STEM Learning Centre: Signal Generator
This 4-minute video sponsored by the UK's National STEM Learning Centre demonstrates how to set up a signal generator using a loudspeaker and an oscilloscope.  If you don't have this equipment, the video also offers great background information on the oscilloscope and how to interpret its read-out in terms of frequency, amplitude, and wave forms.