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Auditory Management and Devices > Characteristics of Compression > Flashcards

Characteristics of Compression Flashcards

1
Q

what are the dynamic and static characteristics of Compressors?

A
  • Dynamic characteristics: determine how quickly the compression operates.
  • Static characteristics: determine when compression is active and the extent of its effect on the gain.
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2
Q

what do diagrams showing compression depict?

A

The waveform Envelope

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2
Q

whats the difference between: attack or activation time & release or recovery time?

A

They’re both dynamic characteristics of compression:

  • Attack or Activation Time: The duration it takes for the hearing aid to engage compression after a change in input or output level.
  • Release or Recovery Time: The finite period required for the hearing aid to disengage compression after a change in input or output level.
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3
Q

What is the typical range for attack times and release times in compression?

A
  • Attack times typically range from 5 to 50 milliseconds.
  • Release times typically range from 20 to 500 milliseconds or greater.
  • some compressors feature adaptive release times, which adjust based on the duration of the increase in input.
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3
Q

What defines fast- acting and slow acting compression?

A
  • Fast-acting compression is characterized by short attack and release times.
  • Slow-acting compression involves long attack and release times.
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3
Q

How can compression be categorized based on its dynamic characteristics?

A

Compression can be classified as fast-acting or slow-acting.

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3
Q

what effect do attack and release times of a compressor have on speech?

A

The attack and release times of a compressor significantly alter its effects on speech syllables.

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4
Q

what is the importance of attack and release times in regards to speech?

A
  • Speech syllables are the most important sounds we need to hear.
  • Great care must be taken when setting the attack and release times.
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5
Q

what are the static characteristics of compression?

A
  • compression ratio
  • compression threshold
  • compression kneepoint
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6
Q

what is compression ratio in audio processing?

A
  • describes the reduction in gain caused by the compressor.

THE DEFINITION:
: the change in input level needed to produce a 1dB change in output level.

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7
Q

what is compression threshold in audio processing?

A

the SPL at which compression starts to act on the signal.

THE DEFINITION:
- The Compression Threshold is the pre-set level above which compression is activated.

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8
Q

what is compression kneepoint?

A

Compression Kneepoint: the SPL at which the compression ratio changes.

THE DEFINITION:
- The pre-set level above which the compression ratio changes.

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9
Q

How does a high Compression Ratio (CR) affect audio output?

A

A high Compression Ratio (CR) results in a small change in output relative to the change in input. This compression leads to a wide range of inputs being compressed into a significantly smaller range of outputs.

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10
Q

What is the Compression Ratio (CR) of linear amplification?

A

Linear amplification typically has a Compression Ratio (CR) of 1:1, meaning there is no compression applied, and the output level mirrors the input level.

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11
Q

What is the difference between effective and actual Compression Ratio (CR)?

A

The effective Compression Ratio (CR) may differ from the actual ratio based on attack and release times.

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12
Q

What Compression Ratios (CRs) are commonly used in hearing aids?

A

Hearing aids often utilize Compression Ratios (CRs) up to 10:1.

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13
Q

How do attack and release times affect the Compression Ratio (CR)?

A

Attack and release times influence the effective Compression Ratio (CR) of a compressor.

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14
Q

How do shorter attack and release times impact the effective Compression Ratio (CR)?

A

Shorter attack and release times result in the effective Compression Ratio (CR) being closer to the actual ratio.

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15
Q

How are levels below the Compression Threshold typically treated?

A

Levels below the Compression Threshold are usually amplified linearly without compression applied.

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15
Q

whats the difference between input and output compression?

A
  • Input controlled compression means the detector is located on the input side of (before) the volume control.
  • Output controlled compression means the detector is located on the output side of (after) the volume control.
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15
Q

how is hearing aid performance affected by input controlled compression?

A

Input control affects the gain (amplification) and MPO (Maximum Power Output) of a hearing aid, but it does not affect the kneepoint, which is the input level at which compression begins.

15
Q

how is hearing aid performance affected by output controlled compression?

A

Volume control affects the gain (amplification) and the kneepoint (threshold where compression begins), but it does not affect the MPO (Maximum Power Output).

15
Q

What factors influence the use of input and output controlled compression in modern hearing aids?

A
  • The wearer’s hearing loss
  • The listening environment
  • The hearing aid settings prescribed by the fitting software
  • The processing algorithms programmed into the hearing aid
16
Q

What is the purpose of compression in audio processing?

A

Compression in audio processing serves to control the dynamic range of audio signals. It reduces the volume of loud sounds while boosting softer sounds, resulting in a more consistent overall volume level.

16
Q

What is WDRC (Wide Dynamic Range Compression) and how does it work?

A

WDRC is a type of compression commonly used in hearing aids and audio processing systems. It dynamically adjusts the gain of different frequency bands based on the input signal, maximizing perceived loudness while maintaining comfort and audibility for the user.

17
Q

What is the purpose of output limiting in audio processing?

A

Output limiting is used to prevent audio signals from exceeding a certain threshold, thereby avoiding clipping and distortion. It ensures that the audio remains within safe levels for listening and protects equipment from damage.

18
Q

What is the purpose of comfort compression in audio processing?

A

Comfort compression aims to make moderate and loud sounds more comfortable for listeners, especially in situations where sudden loud sounds can be jarring or uncomfortable. It achieves this by applying gentle compression to smooth out volume fluctuations.

19
Q

What are the key characteristics of WDRC?

A
  • WDRC has a low kneepoint, meaning it acts on moderate and loud sounds.
  • It typically uses a low compression ratio (less than 2:1) and multiple channels, is input controlled, and results in less distortion and more faithful reproduction of the input sound.
20
Q

What are the key characteristics of Output Limiting in audio processing?

A

Output Limiting is:

  • quick acting,
  • has a high compression ratio above the kneepoint (e.g., 10:1),
  • acts at high levels of sound.
  • It is output-controlled,
  • its parameters might differ at different frequencies.
20
Q

What is syllabic compression and how does it benefit speech processing?

A

Syllabic compression is a technique used in speech processing to reduce the loudness contrasts between different elements of speech, such as syllables or phonemes. It improves speech intelligibility, especially for individuals with hearing impairments or in noisy environments.

21
Q

How does Output Limiting compare to Peak Clipping?

A

Output Limiting has a similar input-output function to Peak Clipping but produces much less distortion, making it a better option for maintaining audio quality.

22
Q

Who benefits from output limiting?

A

Output Limiting is important for individuals with severe to profound hearing losses but is also useful for all types of hearing losses, enhancing the overall listening experience by maintaining safe sound levels.

22
Q

What is the purpose of Wide Dynamic Range Compression (WDRC) in audio processing?

A

WDRC aims to restore loudness reproduction in individuals with moderate hearing losses by ensuring that both moderate and loud sounds are audible and comfortable.

22
Q

Why are multiple channels helpful in WDRC?

A

Multiple channels in WDRC allow for more precise adjustment across different frequencies, enhancing the overall sound quality and ensuring a better listening experience.

23
Q

What should be considered when setting activation times in WDRC?

A

Activation times need to be set carefully to ensure that the compression is effective without causing discomfort or noticeable changes in sound quality, providing a natural listening experience.

23
Q

What are the key characteristics of Comfort Compression?

A

Comfort Compression has a moderate kneepoint, a low compression ratio (often around 4:1), and slow activation times. It is input controlled.

23
Q

How does Comfort Compression compare to WDRC and Output Limiting Compression in terms of its effect on loudness?

A
  • The overall effect on loudness with Comfort Compression is somewhere between Wide Dynamic Range Compression (WDRC) and Output Limiting Compression.
  • It provides a balance by reducing the loudness of sounds to a comfortable level without being as aggressive as Output Limiting or as subtle as WDRC.
23
Q

How does Syllabic or Phonemic Compression affect low and high intensity sounds?

A

It increases gain for low intensity sounds (e.g., the “h” in “has”) and decreases gain for high intensity sounds (e.g., the “a” in “has”).

24
Q

Is Syllabic or Phonemic Compression frequency dependent?

A

Yes, it is frequency dependent.

25
Q

How do modern hearing aids handle interactions between neighboring frequency bands while maintaining effective amplification?

A

One key feature is their ability to divide the signal into different frequency bands.

25
Q

What are the characteristics of Syllabic or Phonemic Compression regarding speed and control?

A

It is fast acting and releasing, and it is input controlled.

26
Q

what is the impact of the duration of deactivation in hearing aids?

A
  • Impact: Significantly affects the sound heard by the hearing aid wearer.
  • Short Deactivation Times: Maintain loudness relationships between parts of speech (e.g., loud vowels vs. quiet consonants).
  • Long Deactivation Times: Maintain comfort when listening in background noise.
27
Q

Where is the kneepoint set in Syllabic or Phonemic Compression?

A

The kneepoint is set at moderate levels.

27
Q

What are some important characteristics of compression?

A
  • Input/output controlled
  • Compression kneepoint or threshold
  • Compression ratio
  • Activation and deactivation times
28
Q

what are the uses of compression?

A
  • Output limiting – fast acting output controlled compression
  • Reducing intensity differences within the speech signal - syllabic or phonemic compression
  • Decrease long term level differences in the speech signal - slow acting input controlled compression
  • Increase sound comfort - input controlled compression
  • Normalise speech loudness - compression ratio decreases as input level increases
  • Noise Reduction - compression is used as part of digital signal processing
29
Q

What purpose does dividing the signal into frequency bands serve?

A

Dividing the signal allows for customization of compression characteristics for each frequency band.

30
Q

What is WDRC and how is it applied in modern hearing aids?

A

WDRC stands for Wide Dynamic Range Compression. It’s applied in modern hearing aids to adjust amplification based on the variation in dynamic range across the audiogram.

31
Q

How do modern hearing aids handle the interaction between neighboring frequency bands?

A

While there can be some interaction between neighboring bands, modern hearing aids are designed to minimize this interaction while still providing effective amplification across different frequencies.

32
Q

What is expansion in the context of hearing aids?

A

Expansion is the opposite of compression, where the gain increases as the input level increases, amplifying louder sounds more than softer ones.

32
Q

Who might find expansion useful in hearing aids?

A

Expansion can be beneficial for individuals with good low-frequency hearing but a moderate loss at mid and high frequencies, as well as those sensitive to internal noise from the hearing aid or find low-level background noise distracting.

32
Q

What drawback is associated with expansion in hearing aids?

A

However, expansion can affect hearing for speech in low-level noise, potentially impacting speech perception in such environments.

Auditory Management and Devices (14 decks)

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