Complex Sound, Common Types of Tones, and Noise

Pure tone

The simplest sound, one with a single frequency. Most common stimuli used for testing hearing.

Complex sounds

Made up of pure tones mixed together.

“In phase”

Sine waves that had the same phase. The energy in the two waves can be combined to produced a summed wave.

“Out of phase”

Sine waves that have different phases. The energy in the two waves cancels to produce a summed wave (and in some cases, no wave at all).

Complex wave

When tones of different frequencies are combined.

Spectrum

A graph that shows the energy present in a sound as a function of the frequencies making up that sound.

Vertical line on a spectrum

Represents the intensity of the tone at that frequency.

Distortion

Changes in a sound due to inaccurate production, transmission, or reproduction.

Distortion is due to

nonlinear and asymmetric vibration.

Harmonics

Whole number multiples of the fundamental frequency of a complex sound.

Fundamental frequency

the lowest frequency of a complex sound

Square wave

Waveform that immediately transitions from full compression to full rarefaction

Triangular wave

waveform with compression and rarefaction peaks

Sawtooth wave

waveform with an immediate transition from either full compression to full rarefaction, or vice versa, followed by a steady transition to the opposite phase.

Amplitude modulated tones

waveforms where the intensity is increased and decreased.

Frequency modulated tones

waveforms where the frequency changes; the tone does not stay at a constant frequency

White noise

Gaussian noise. Noise with equal amounts of energy at each frequency

Pink noise

Noise with less high frequency energy.

Clicks

Transient signals of very short duration.

Acoustic filtering

Removing specific frequency information and done through the use of computer software.

High-pass filter

"Low-cut filter.” Used to remove low-frequency information. All frequencies above the cutoff frequency will be filtered through.

Low-pass filter

“High-cut filter.” Used to remove high-frequency information. All frequencies below the cutoff frequency will be filtered through.

Band-pass filter

Used to remove some low-frequency and some high-frequency information. Only frequencies above the high-pass cutoff and below the low-pass cutoff frequencies will be filtered through