In the next few modules we will explore in reasonable detail the description of signals in the frequency domain.  Using frequency rather than time to look at a signal gives us a number of insights about the way we hear and about the nature of musical tones.  Although we do not cover these topics in strict order here are some of the key questions that you should be have an answer for by the end the your study of this section. 

• What constitutes the difference between a musical tone and a recognizable sound like a dog's bark or a chicken's cluck?
• What is the difference between a pure and a complex tone?
• What is Fourier's theorem and why do I care?
• What do the terms spectrum and timbre mean and how are they  related?
• What is the fundamental of a complex tone?
• What are harmonics and how are they numbered?
• Can I associate a frequency with a musical note even if that frequency is not present in the note? (Surprisingly, yes!)
• Is there a mechanical spectrum analyzer in my ear? (Eeek, get it out!)
• What is noise?

As with the previous module on decibels you should go through the pages sequentially and do the self test exercises to make sure that you are following the logic.  The good news is that this section is much less mathematical and considerably more aural and visual.  There are sound files associated with a number of the figures so I hope you are at a computer configured to play sound files. Read, listen, and enjoy! 

1. Time and Frequency
2. Sounds, Pure Tones, and Complex Tones 
3. Fourier's Theorem
4. The Fourier Transform: Decomposing Time-Domain Signals