Auditory Masking

Summary

This video explains auditory masking, focusing on how human hearing thresholds are affected by different types of sounds. It covers spectral masking (the influence of background noise and tones on hearing thresholds) and temporal masking (how time delays impact auditory perception). Key concepts include the threshold of hearing, the effect of broadband noise and tonal masking on frequencies, and the way the brain processes sounds over time. The video provides real-world examples and explores how the loudness of masking sounds alters perception, as well as the complex ways in which we hear sounds close together in time.

Takeaways

• 😀 The human hearing threshold refers to the quietest sound that can be detected by the average human ear across various frequencies.
• 🎧 Human hearing ability spans roughly between 20 Hz and 20 kHz, though it can vary slightly between individuals.
• 🔊 Background noise, such as broadband white noise, can raise the hearing threshold, making it harder to hear certain frequencies.
• 📉 The threshold of hearing can change with different sound environments, notably with the presence of background noise.
• 🔔 Spectral masking occurs when the presence of another sound modifies the hearing threshold for a specific frequency, making it harder to hear certain tones.
• 📏 Temporal masking refers to the impact of time on the human auditory system's ability to detect sounds, where sounds near a masker are harder to hear.
• 🎶 Tones masked by broadband noise, such as white noise, raise the hearing threshold and make certain tones less detectable.
• 🎵 Tones masked by other tones show how masking affects specific frequencies depending on their proximity in frequency range to the masking tone.
• 📊 Zwicker's work on tonal masking reveals that a loud masking tone can distort the hearing threshold, making nearby tones harder to detect.
• ⏰ Temporal masking also has pre-masking and post-masking effects, where sounds close to the masker (before or after) may not be perceived.
• 🎧 The time delay in auditory perception means that short sounds before or after a masker can go unnoticed, due to the response time of the cochlea and eardrum.

Q & A

What is the human hearing threshold in quiet?

The human hearing threshold in quiet refers to the lowest sound pressure level that can be heard by an individual in the absence of any background noise. This threshold varies across the frequency spectrum, but it generally falls between 20 Hz and 20 kHz for most people.

What effect does background noise, like white noise, have on the hearing threshold?

Background noise, such as white noise, raises the hearing threshold, meaning it makes it more difficult for us to hear softer sounds. This effect is most pronounced in the middle frequencies, while the extreme ends of the frequency spectrum are less affected.

How does spectral masking work?

Spectral masking occurs when the presence of other sound frequencies, like broadband noise or other tones, alters the human hearing threshold. For example, if a broadband noise is present, it raises the hearing threshold, making it harder to perceive tones or sounds at lower levels.

How does tonal masking differ from broadband noise masking?

Tonal masking occurs when a tone at a specific frequency affects the ability to hear other tones, particularly those at frequencies higher than the masker tone. In contrast, broadband noise affects a broader range of frequencies and raises the hearing threshold across all frequencies more uniformly.

What is the significance of the bark scale in auditory masking?

The bark scale is used to describe the critical bands of hearing. It helps determine how different frequencies are perceived by the human ear, with a focus on how the brain groups sounds. The bark scale plays a key role in assessing whether one sound will mask another based on their frequency difference and amplitude.

How can we use Zwicker's chart to predict masking effects?

Zwicker's chart is used to determine whether a test tone will be masked by a masking tone based on their frequency difference (in bark) and the masking tone's amplitude. By plotting the levels of both tones, we can assess whether the test tone falls below the masking threshold and is thus masked.

What is the difference between pre-masking and post-masking?

Pre-masking refers to sounds that occur before the masking sound, which may not be perceived by the listener. Post-masking refers to sounds that occur after the masking sound has ended, which can also be masked. Both effects are due to the time it takes for the human auditory system to adjust to sound changes.

How does temporal masking affect our perception of sounds?

Temporal masking affects our perception by preventing us from hearing sounds that occur close in time to a masking sound. This can occur both before the masker (pre-masking) and after the masker (post-masking), and it takes time for our hearing system to recover to the normal threshold.

Why is the frequency difference between the masker and test tone important in tonal masking?

The frequency difference between the masker and test tone is crucial in tonal masking because the closer the frequencies are, the more likely the masker will affect the test tone. When the frequencies are further apart, the masking effect is less significant, and the test tone is more likely to be heard.

What role does amplitude play in auditory masking?

Amplitude plays a significant role in both spectral and tonal masking. The louder the masker tone or noise, the greater its ability to raise the hearing threshold and mask other sounds. A higher amplitude masker will cover a wider range of frequencies or even mask sounds that are at higher frequencies.