# Lesson 15 — Frequency Domain and Ideal Filters

<p class="block-synopsis">Time versus frequency, bandwidth, and the four ideal filter types.</p>

**Objectives covered**

- **2.1** — I can graph a given sinusoidal signal, including DC components, in both the time and frequency domains and determine its bandwidth.
- **2.2** — I can identify types of ideal filters, determine their cutoff frequencies, and analyze their output given an input sinusoidal signal or signal spectrum.

:::{admonition} Due at this lesson
:class: warning

Quiz 3 (Obj 1.6–1.7) — due 21 Sep 2359
:::

<div class="block-toc">
  <a class="bt-card bt-reading" href="../Block2Reading/Obj01/ECE215_B2_Obj01_Reading.html">
    <span class="bt-kind">Reading · Objective 2.1</span>
    <h4>The Frequency Domain</h4>
    <p>The course reading for Objective 2.1.</p>
  </a>
  <a class="bt-card bt-reading" href="../Block2Reading/Obj02/ECE215_B2_Obj02_Reading.html">
    <span class="bt-kind">Reading · Objective 2.2</span>
    <h4>Ideal Filters</h4>
    <p>The course reading for Objective 2.2.</p>
  </a>
  <a class="bt-card bt-flashcards" href="L15_Flashcards.html">
    <span class="bt-kind">Flashcards</span>
    <h4>Review deck</h4>
    <p>Key terms, equations, and ideas from this lesson, in a self-test deck.</p>
  </a>
  <a class="bt-card bt-slides" href="../_static/slides/ECE_215_Lesson15.pdf">
    <span class="bt-kind">Slides</span>
    <h4>Lesson 15 deck</h4>
    <p>The slides used in class, as a PDF.</p>
  </a>
  <a class="bt-card bt-practice" href="../downloads.html">
    <span class="bt-kind">Practice Problems</span>
    <h4>Work these before the quiz</h4>
    <p>Ungraded problems with answers, on the downloads page.</p>
  </a>
  <a class="bt-card bt-demo" href="https://usafa-ece.org/apps/filter-demo/" target="_blank" rel="noopener">
    <span class="bt-kind">Demo ↗</span>
    <h4>Filter Demo</h4>
    <p>Hear low-, high-, and band-pass filters applied to live audio.</p>
  </a>
</div>