What type of graph depicts amplitude over frequency?

The correct answer is the spectrum, which is a type of graph that represents the amplitude of various frequency components of a sound signal. In a spectrum graph, the x-axis typically displays frequency (usually measured in Hertz), while the y-axis shows amplitude (often represented in decibels). This allows for a clear visualization of how much energy or power is present at each frequency, making it an essential tool in analyzing the frequency content of sounds.

This type of graph is particularly useful in speech science because it helps researchers and clinicians understand the phonetic characteristics of speech sounds, identify formants (which are resonant frequencies important for vowel sounds), and analyze the acoustic properties of different sounds in a more detailed manner compared to other types of graphs.

In contrast, a waveform graph represents how amplitude changes over time, showing the sound wave's shape rather than its frequency components. A sonogram provides a time-frequency analysis of sound, displaying frequency changes over time but not focusing solely on amplitude across a specific frequency range. A formant graph specifically displays the formants of speech sounds, which are peaks in the spectrum related to resonances in the vocal tract, rather than showing a broad amplitude vs. frequency analysis.