Waveform

Definition

A waveform is one way that the acoustic properties of speech can be visualized. Waveforms measure the changes in air pressure over time during speech. Differences in air pressure arise as a result of air particles being compressed and rarefied, giving rise to “sound waves.” Waveforms measure the frequency and amplitude of sound waves.

• Frequency illustrates the pitch of a sound. The frequency of sound waves refers to the amount of cycles per second. A higher frequency (waves closer together) results in a higher pitch sound where a lower frequency (waves further apart) of sound waves results in a lower pitched sound.

• Amplitude is plotted across the y-axis of a waveform and refers to the “loudness” of a sound. Amplitude measures the amount that air particles move during sound production. A louder sound results in air particles moving more, creating a higher peak on the waveform. The units that amplitude is reported in is called decibels.

A spectrogram is another method of visualizing the acoustic properties of speech, discussed here.

Examples

• Hul’q’umi’num’: this example provided by Marshall and Bird (2018, p. 116) illustrates both a waveform (top) and spectrogram (middle) and its corresponding phonemes (bottom 4 rows).
  • Looking at the waveform, it can be seen that the vowel (a) is the loudest. This is represented by the highest peaks (higher amplitude) of the waveform. The nasal n and the lh are the sounds with the lowest amplitudes, which can be seen by the lower peaks in the waveform. This means, that the vowels are louder and the nasals are quieter.