# Lecture 3 Blog, ECE301 Spring 2011, Prof. Boutin

Friday January 14, 2011 (Week 1) - See Course Schedule.

In the third lecture, we finished discussing the last basic transformations of the independent variable (time scaling) and showed how the three basic transformations can be used to write a tune starting from a single pure sine wave such as an A440. We then defined the concept of "periodic signal", both for CT and for DT. (Recall that the main difference with DT is that the shift must be an integer.) We pointed out that a method for building a periodic signal starting from any function. The method consists in adding an infinite number of shifted copies of the function. It is a VERY IMPORTANT construction which will be used several times in ECE301 and beyond.

## Action items before the next lecture:

• Solve the following practice problems on transformations of the independent variable. (Be careful with this one!!)
• Read Section 1.3 in the book (sorry I forgot to write this earlier.--Mboutin 13:13, 19 January 2011 (UTC))