Broad-band sounds vs. Pure tone

Question 0

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Sound localization

Answer 0

Sound localization involves processing both intensity differences (differences in loudness at the two ears) and latency differences (differences in the time of arrival of sounds between two ears). Time delay provides a strong directional cue.

Question 1

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Pure tone definition

Answer 1

A tone with a single frequency of vibration

Question 2

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Low frequencies

Answer 2

At low frequencies, no matter where sounds are presented horizontally around the head, there are virtually no intensity differences between the ears - differences in times of arrival are the principal cues for sound position.
Tones at low frequencies (broadband) have wavelengths longer than the distance between the ears and are relatively easy to localize.

Question 3

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Higher frequencies

Answer 3

At higher frequencies, the sound shadow cast by the head produces significant binaural intensity differences.
Pure tones at higher frequencies present ambiguity in the determination of correct time delay, which may be a greater than the signal period, and are much harder to localize
Fortunately, pure tones are fairly uncommon in nature, and high-frequency noises are usually complex and random enough to allow unambiguous interaural delay estimation.

Question 4

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Broad-band sound

Answer 4

A broad-band sound contains harmonics, or multiple fundamentals (basic frequency), where each frequency has a unique sound.
Each fundamental sound has a different amplitude, or intensity, which makes it easy to find the source of that particular sound quality, or timbre.
For example, if the same note is played by various instruments, it’s easier to localize the sound from each instrument due to the amplitude (intensity) unique to each specific instrument, compared by the same note played by multiple musicians with the same instrument.

Question 5

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Interaural intensity difference (IID)

Answer 5

Caused mostly by the shading effect of the head

Question 6

Explain why it is easier to localize the source of a broad-band sound (one with many harmonics), than it is to localize the source of a pure tone (one with NO harmonics).
Inter-aural time difference (ITD)

Answer 6

Differences between times that signals reach each ear