Seminar 2: Compression Flashcards
1
Q
What is the range of sounds that the normal auditory system can cope with?
A
The normal auditory system can cope with a range of sounds from 0 to 100 dBHL (decibels Hearing Level).
2
Q
How does the range of sounds that an impaired auditory system can cope with compare to a normal auditory system?
A
An impaired auditory system can cope with a smaller range of sounds, meaning the patient has a reduced dynamic range.
3
Q
What is the purpose of a system that limits the maximum output for hearing-impaired individuals?
A
To avoid exceeding the individual’s discomfort levels and to prevent saturation of the hearing aid.
3
Q
Why is the range of sounds important in the context of auditory systems?
A
The range of sounds is important because it determines the dynamic range that an auditory system can handle, which affects the ability to hear and process different sound levels effectively.
4
Q
Why is it important to decrease the range of sound levels in speech and the environment for hearing-impaired individuals?
A
To better match the residual dynamic range of the hearing-impaired individual, ensuring they can hear effectively without discomfort.
5
Q
What are the characteristics of vowel sounds such as /a/, /u/, and /i/?
A
Vowel sounds are low-pitched, relatively intense, and primarily responsible for making speech audible.
6
Q
What is the range of average conversational speech according to Beranek (1947)?
A
Average conversational speech spans a range of 30dB.
7
Q
How many syllables per second are typically spoken in normal speech?
A
3 to 5 syllables per second.
7
Q
What are the characteristics of consonant sounds, especially unvoiced sounds like /th/, /f/, and /s/?
A
Consonant sounds are high-pitched, relatively soft, and carry most of the information in speech.
7
Q
What are the typical durations for stressed and unstressed vowels, and voiced and unvoiced consonants?
A
Stressed vowels: 100 - 200 ms
Unstressed vowels: 75 - 150 ms
Voiced consonants: 50 - 150 ms
Unvoiced consonants: 20 - 100 ms
8
Q
What is the formula for the output of a hearing aid?
A
Output = Input + Gain (where Gain = Output - Input).
9
Q
hat does a frequency response curve represent in the context of hearing aids?
A
It represents the hearing aid output as a function of frequency with fixed input level and overall gain.
9
Q
What is a frequency-gain curve?
A
A graph showing the gain of a hearing aid as a function of frequency.
10
Q
What changes might occur to frequency response curves for speech presented at different input levels?
A
The shape of the curve may change as the input level increases.
10
Q
On what factors can the gain from a hearing aid vary?
A
- The frequency of sound.
- The intensity of the input at each frequency.
11
Q
What is shown by the input-output function of a hearing aid?
A
The variation in gain across different input intensities at a specified frequency.
12
Q
- What is the output when the input is 50 dBSPL and the gain is 30dB?
- What is the output when the input is 90 dBSPL and the gain is 20dB?
- What happens to the hearing aid output for an input of 90 dBSPL?
A
- The output is 80 dBSPL (50 + 30).
- The output is 110 dBSPL (90 + 20).
- The hearing aid provides only 20dB of gain, resulting in an output of 110 dBSPL.
12
Q
How do the input/output functions differ among three different hearing aids for inputs of 50 and 90 dBSPL?
A
The input/output (I/O) functions vary between hearing aids, resulting in different outputs for the same input levels. For instance, one hearing aid may produce an output of 80 dBSPL when the input is 50 dBSPL, indicating a gain of 30dB. Similarly, another hearing aid may yield an output of 110 dBSPL with an input of 90 dBSPL, suggesting a gain of 20dB. These variations demonstrate how different devices apply gain differently based on input levels.
13
Q
How does linear amplification behave in terms of gain adjustment at different input levels?
A
In linear amplification, the gain remains constant regardless of input intensity at specific frequencies. For instance, at 0.5kHz, the gain will be 11dB irrespective of whether the input level is 10dB SPL, 50dB SPL, or 80dB SPL. Similarly, at 4kHz, the gain remains constant at 20dB for different input levels. However, linear amplification has a limit to its output, and its linearity decreases at high input levels.
13
Q
What is the relationship between input and gain for these hearing aids?
A
The input/gain (I/G) function reveals how much gain is applied for different input levels. In the case mentioned, one hearing aid provides 30dB of gain for an input of 50 dBSPL but only 20dB of gain for an input of 90 dBSPL. This indicates that the gain decreases with increasing input level. Despite the decrease in gain, the output continues to increase, suggesting that the decrease in gain is less than the increase in input level.
13
Q
What is the relationship between input and output in linear amplification?
A
In linear amplification, the input/output (I/O) relationship follows a 1:1 ratio for every 10dB increase in input level, resulting in a corresponding 10dB increase in output level. This relationship continues until the maximum output is reached. It’s important to note that the gain of the hearing aid remains constant at 30dB until the maximum peak output (MPO) is reached.
13
Q
How does the input level and gain adjustment affect the output of Hearing Aid 3?
A
Hearing Aid 3 applies a gain of 17dB to an input of 90 dBSPL, resulting in an output of 107 dBSPL. This illustrates that even though the gain decreases with increasing input level, the output continues to increase. This occurs because the decrease in gain is less than the increase in input level. Additionally, for Hearing Aid 3, applying 30dB of gain to an input of 50 dBSPL results in an output of 80 dBSPL, while applying 20dB of gain to an input of 90 dBSPL results in an output of 110 dBSPL. Despite the difference in gain applied to the inputs, the output sound pressure level (SPL) is still greater for the 90 dBSPL input.
14
Q
What are the differences between linear and compression amplification in addressing sensorineural (SN) loss?
A
Linear amplification applies the same amount of gain to all sounds, resulting in soft sounds becoming audible, conversational speech becoming loud, and intense sounds being amplified beyond the dynamic range, making them uncomfortable. In contrast, compression amplification applies different amounts of gain to soft, moderate, and intense sounds, resulting in a more balanced listening experience. Soft sounds become audible, moderate sounds are comfortable, and intense sounds are loud but still comfortable.
15
Q
How does the input/gain (I/G) function change in linear amplification for input levels exceeding 80 dBSPL?
A
In linear amplification, the reduction in gain occurs for input levels greater than 80 dBSPL. This reduction is necessary because the maximum output cannot exceed 110 dBSPL due to limitations in the hearing aid’s capabilities. As a result, the gain decreases to prevent the output from exceeding the maximum limit, ensuring that the output remains within the desired range for comfortable listening.
16
What is peak clipping in hearing aids?
Peak clipping is a method used to control the Maximum Peak Output (MPO) of a hearing aid. Once the output reaches a certain level, the device cannot produce a louder signal, limiting the loudness to within the wearer's dynamic range.
17
What is the Maximum Peak Output (MPO) of a hearing aid?
The MPO represents the highest possible signal that a hearing aid can deliver, regardless of the input level or gain. It is determined by the characteristics of the microphone, amplifier, and receiver.
18
What is the Maximum Peak Output (MPO) of a hearing aid?
The MPO refers to the highest possible signal that a hearing aid can deliver, regardless of the input level or gain settings. It is determined by the characteristics of the microphone, amplifier, and receiver components within the hearing aid.
18
Why is peak clipping used despite its distortion of the output signal?
Peak clipping is employed as a method to control or limit the MPO of a hearing aid, ensuring that the output remains within safe levels for the wearer.
While it introduces distortion, it prevents the device from producing excessively loud signals that could potentially damage hearing or cause discomfort.
18
How does peak clipping affect the output signal of a hearing aid?
When the input level and gain settings exceed the MPO, the hearing aid enters saturation, causing the peaks of the output signal to be clipped at the maximum output level.
This process, known as peak clipping, results in a distorted output signal, often described as sounding "scratchy."
18
What is peak clipping in the context of hearing aids?
Peak clipping is a method used to control or limit the Maximum Peak Output (MPO) of a hearing aid.
Peak clipping is a basic method used to limit the output of a hearing aid by clipping the peaks of the waveform when the signal becomes too loud.
This helps to ensure that the loudness of the signal remains within the wearer's dynamic range.
18
What is a drawback of peak clipping as an output limiting method?
Despite its effectiveness in controlling loudness, peak clipping introduces distortion into the waveform, resulting in a degraded sound quality.
This distortion can make the sound appear "scratchy" or unnatural, making peak clipping less than ideal for output limiting in hearing aids.
18
How does peak clipping affect the loudness of the signal?
Peak clipping reduces the loudness of the signal by limiting the amplitude of the peaks, preventing them from exceeding a certain level. This helps to protect the wearer's ears from overly loud sounds.
19
What does distortion refer to in the context of hearing aids?
Distortion in hearing aids refers to the presence of frequency components in the output signal that were not present in the original input signal. This can result in altered or unnatural sound quality.
20
What is Total Harmonic Distortion (THD)?
Total Harmonic Distortion (THD) is a measure of the summed power of all the harmonic distortion products relative to the power of the original input signal.
It is expressed as a percentage and provides an indication of the overall level of harmonic distortion present in the output signal.
20
What is harmonic distortion?
Harmonic distortion occurs when additional frequencies, known as harmonics, are generated at integer multiples of the original input frequency. For example, if the input signal is 500 Hz, harmonics would occur at 1000 Hz, 1500 Hz, 2000 Hz, and so on.
21
How does distortion affect the performance of hearing aids?
- Distortion, whether harmonic or intermodulation, can result in unpleasant sound quality and may adversely affect speech intelligibility.
- It can distort the original sound, making it difficult for wearers to understand speech or discern other environmental sounds accurately.
21
What is intermodulation distortion?
- Intermodulation distortion occurs when two frequencies are presented simultaneously to a system, and the output contains additional frequencies that are related to the sum and difference of the original input frequencies.
- This can result in unwanted frequency components being introduced into the output signal.
22
What methods can be used for output limiting in hearing aids?
Output limiting can be achieved using either Peak Clipping (PC) or Compression, also known as Automatic Gain Control (AGC) or Automatic Volume Control (AVC).
22
what is The Problem with Linear Amplification
*Overamplification:
- Many people with sensorineural hearing loss have reduced dynamic range
- In these cases linear hearing aids can amplify to levels above the wearers ULLs causing discomfort
- In some cases this is severe enough to stop people using hearing aids
- We can resolve this problem by limiting the output of the hearing aid
22
What is the purpose of output limiting in hearing aids?
- Output limiting in hearing aids aims to reduce the dynamic range of incoming signals to match the dynamic range of the wearer's hearing.
- This ensures that both soft and loud sounds are amplified appropriately, enhancing overall audibility and comfort.
23
Why is compression considered a better option for output limiting in many cases?
- Compression is often preferred over peak clipping for output limiting in hearing aids for several reasons, which will be discussed later.
- These reasons likely include its ability to preserve the natural dynamics of speech and environmental sounds, its adaptability to different input levels, and its potential to reduce distortion compared to peak clipping.
24
How does compression affect the gain in a hearing aid?
Compression adjusts the gain at each frequency based on the input intensity (loudness) to the hearing aid.
The gain varies for different input levels, with quieter sounds receiving higher gain and louder sounds receiving lower gain.
25
What are the dynamic and static characteristics of compressors?
- Dynamic characteristics include parameters like attack and release times, which determine how quickly the compression operates.
- Static characteristics include compression threshold, compression ratio, and compression kneepoint, which determine when compression is active and the extent of its effect on the gain.
25
What is the purpose of compression in hearing aids?
- Compression compresses (squashes) the range of input sound intensities into a smaller range of output intensities.
- This helps reduce the dynamic range of the output, making it more comfortable for the wearer by ensuring that both soft and loud sounds are amplified appropriately.
26
What is compression threshold, and how does it relate to compression kneepoint?
- Compression threshold (CT) is the sound pressure level (SPL) at which compression begins to act on the signal.
- The compression kneepoint (TK) is the SPL at which the compression ratio changes.
- These terms are often interchangeable, and the point at which the slope changes indicates the compression threshold or kneepoint.
27
What is the compression ratio (CR) in hearing aids?
The compression ratio (CR) determines how much the input signal will be compressed. It is the ratio of the change in input to the resulting change in output.
28
How is compression ratio calculated?
Compression ratio is calculated as the change in input (∆Input) divided by the change in output (∆Output)
e.g. if increasing the input from 20 to 40 dB SPL (∆Input = 20 dB) results in an output increase from 60 to 80 dB SPL (∆Output = 20 dB), the CR is 20/20 = 1:1 (linear). If the input increases from 60 to 80 dB SPL and the output increases from 90 to 100 dB SPL, the CR is 20/10 = 2:1.
29
What are high and low compression ratios used for?
- High compression ratios (CR of 5.0 or greater) are used to limit the output so that it does not exceed the individual's loudness discomfort levels.
- Low compression ratios (CR between 1.0 and 5.0) are used to improve the audibility of softer components of speech and restore loudness perception.
30
How do high compression ratios affect sound quality?
High compression ratios can adversely affect the clarity and pleasantness of the amplified sound.
31
What is the waveform envelope in the context of compression?
The waveform envelope is an imaginary line drawn around the extremities of the wave, often depicted in diagrams showing compression to illustrate how the amplitude of the wave is affected.
32
What is attack time (AT) in hearing aids?
Attack time (AT) is the time delay between the onset of an input signal loud enough to activate compression (when it exceeds the threshold kneepoint, or TK) and the resulting reduction in gain.
33
How does ANSI (2014) define attack time?
ANSI (2014) defines attack time as the time between an abrupt increase in input level from 55 to 90 dB SPL and the point where the output level stabilizes within 3 dB of the steady value for an input of 90 dB SPL.
33
How long is the typical attack time for hearing aids?
Attack times typically range from 5 to 50 milliseconds.
34
What are dynamic characteristics of compressors in hearing aids?
- Dynamic characteristics of compressors include attack time (AT) and release time.
- These characteristics determine how quickly the compression operates.
34
What happens when the input increases above the threshold kneepoint (TK)?
- When the input increases above the TK, the gain of the hearing aid does not change immediately, resulting in an overshoot in the output.
- As the gain approaches its target, the output of the hearing aid also stabilizes, reaching within 3 dB of its final value.
35
What are the benefits of a fast attack time (AT) in a compression system?
- The faster the AT, the shorter the duration of the overshoot and the shorter the period of time the individual has to listen to sounds louder than desired.
- Fast attack times, such as those as quick as 5 milliseconds, are desirable when compression is used to limit the maximum output.
35
What might be a drawback of having both fast attack and release times (RT) in a compression system?
Having both fast AT and RT may be undesirable because the gain will vary in response to each cycle of the incoming signal, which can result in a distorted waveform.
35
What is the purpose of the attack time in compression?
- The purpose of the attack time is to manage the gain reduction in response to sudden increases in input level, preventing overshoot in the output and stabilizing the hearing aid’s response to changes in sound intensity.
36
What are static characteristics of compressors in hearing aids?
- Static characteristics determine when compression is active and the extent of its effect on the gain.
- These include compression threshold, compression ratio, and the compression kneepoint.
37
What is considered a fast release time (RT)?
An RT of 20 milliseconds is considered fast.
38
How do attack and release times affect the user's experience with a hearing aid?
- Fast AT ensures that loud sounds are quickly controlled, preventing discomfort from sudden loud noises.
- However, if both AT and RT are too fast, it can lead to a distorted sound experience as the hearing aid constantly adjusts the gain for each sound cycle.
- Balancing AT and RT is crucial for maintaining sound quality and user comfort.
39
Why is the release time generally longer than the attack time?
The release time is generally longer to ensure that the gain does not change too rapidly in response to each sound cycle, which helps to avoid distortion and maintain sound quality.
40
What are the disadvantages of attack times (ATs) and release times (RTs) between 100 milliseconds and 2 seconds?
Although gain may be reduced in the presence of speech, it will increase during pauses between words, resulting in a pumping sensation where the background noise level increases during pauses and decreases when speech is present.
41
Why is the pumping sensation less problematic with AT and RT faster than 100 milliseconds?
Faster AT and RT cause gain changes to occur too quickly to be perceived, minimizing the pumping sensation.
42
What effect does a fast attack time coupled with a very slow release time have?
A fast AT and slow RT (greater than or equal to 2 seconds) can adversely affect the audibility of speech that follows immediately after a gain reduction due to a transient sound like a pen click.
43
How do attack and release times of 2 seconds or slower function in a compression system?
These times respond to changes in the overall sound level of the environment rather than to individual sound events.
44
What is adaptive release time in a compression system?
- Adaptive or variable release times adjust the RT based on the duration of the input signal.
- For brief, transient sounds, the RT is fast to minimize the impact on subsequent speech audibility.
- For sustained inputs, the RT is slower, acting similarly to a manual volume adjustment.
45
How does linear gain affect the temporal envelope for speech in quiet conditions?
Linear gain results in the greatest increase in the temporal envelope for speech in quiet conditions but may be less effective in noisy environments or for louder input levels.
45
How do compression ratio (CR) and attack/release times interact?
- CRs are determined from steady signals. With time-varying inputs like speech, the effective CR is significantly affected by AT and RT.
- Fast AT and RT amplify softer speech components more than louder ones, resulting in an effective CR similar to steady signals.
- Slow AT and RT result in a lower effective CR for speech.
45
What is the main consequence of significant inner hair cell damage in individuals with severe to profound hearing loss?
- The main consequence is broadened auditory filters, which leads to a loss of frequency selectivity.
- This reduces the ability to separate two signals in the frequency domain, making it more difficult to hear in background noise.
46
How do fast versus slow attack and release times affect average conversational speech?
- Fast ATs and RTs are more detrimental to perceived sound quality at high CRs than at low CRs.
- The range between the upper and lower limits of speech is smaller with fast AT and RT, indicating more signal compression, compared to slow AT and RT.
47
How does reduced frequency selectivity affect hearing in noisy environments?
- More noise passes through the auditory filter, masking the target signal.
- Reduced frequency selectivity leads to greater reliance on temporal cues, making individuals more susceptible to distortion of those cues with amplification.
48
How does the dynamic range of a 65 dB speech-in-quiet signal compare between linear gain, slow compression, and fast compression settings?
The dynamic range of the signal increases by up to 9 dB for the linear gain setting and up to 5 dB for the slow compression setting when compared to fast compression.
48
What percentage of severe to profound (S2P) hearing loss clients cannot acclimatize to fast compression, according to Turton & Smith (2013)?
20% of S2P clients cannot acclimatize to fast compression.
49
What are the effects of activation and deactivation times on the sound heard by the hearing aid wearer?
- Short times: Helpful for maintaining loudness relationships between different parts of speech, such as loud vowels and quiet consonants.
- Long times: Helpful for maintaining comfort when listening in background noise.
49
Does the threshold knee point (TK) or compression ratio (CR) change when adjusting the volume control in AGC-I?
No, neither the TK nor the CR changes when the volume control is adjusted.
49
What is syllabic or phonemic compression designed to do?
- Syllabic or phonemic compression is designed to reduce contrasts in the intensity of syllables by increasing gain for low-intensity sounds (e.g., the "h" in "has") and decreasing gain for high-intensity sounds (e.g., the "a" in "has").
- It is frequency-dependent, fast-acting, and input-controlled with a kneepoint at moderate levels.
49
What happens when the input exceeds the threshold knee point (TK) in AGC-I?
When the input exceeds the TK, the compressor is activated, and gain is reduced at the pre-amplifier.
49
What are AGC-i and AGC-o circuits?
- AGC-i (input-controlled): Compression is based on the input signal level.
- AGC-o (output-controlled): Compression is based on the output signal level.
49
Where is the level detector located in input-controlled compression (AGC-I)?
The level detector is located before the volume control, and the compression acts on the input to the hearing aid.
49
How does rotating the volume control affect the compression parameters in AGC-I?
- Rotating the volume control from full-on to -20dB decreases the gain above and below the threshold knee point, but it does not impact the TK or the compression ratio (CR).
- The input above the TK (e.g., 40 dB) still activates compression, and the amount of compression stays the same.
49
Where is the level detector located in output-controlled compression (AGC-O)?
The level detector is located after the volume control, and the compression acts on the output of the hearing aid.
49
What does automatic gain control (AGC) refer to in the context of compression circuits?
- AGC refers to compression circuits where the amount of gain applied is automatically determined by the signal level.
- A level detector is essential for this process, and its position relative to the volume control influences the circuit's operation.
49
What triggers the compressor in AGC-O?
The compressor is activated once the output exceeds the threshold knee point (TK).
50
How does rotating the volume control affect the compression parameters in AGC-O?
Rotating the volume control from full-on to -20dB decreases the gain. More importantly, it results in an increase in the TK.
50
What happens to the input level required to activate the compression circuit when the volume control is adjusted in AGC-O?
The input level has to increase before the compression circuit is activated when the volume control is turned down.
51
What are frequency bands in hearing aids?
- Frequency bands are independently controlled areas for gain adjustment only.
- Increasing or decreasing the gain in a frequency band equally affects the response to soft, moderate, and intense sounds at frequencies within that band without affecting the compression parameters.
52
What are compression channels in hearing aids?
- Compression channels allow separate adjustments for soft and intense input levels.
- Changes within a compression channel may affect the compression ratio (CR) and/or the threshold knee point (TK), in addition to gain.
- The effect on moderate-level inputs depends on the compression system.
52
Can changes be made across multiple frequency bands and/or compression channels in hearing aids?
- Yes, depending on the hearing aid manufacturer, it may be possible to make changes across multiple frequency bands and/or compression channels.
- Multiple channels are separated by crossover frequencies, which may also be adjustable.
53
What is expansion in hearing aids?
- Expansion decreases the gain as the input level decreases, counteracting the additional gain provided by Wide Dynamic Range Compression (WDRC) for soft inputs.
- This helps reduce the amplification of soft ambient sounds, such as a computer or refrigerator, while maintaining increased speech intelligibility for soft speech and normalized loudness perception.
53
What is the advantage of multichannel compression in hearing aids?
- Multichannel compression ensures that acoustic events in a discrete frequency region do not affect the response of the hearing aid at all frequencies.
54
What is the typical hearing loss pattern in sensorineural hearing loss (SNHL)?
SNHL is characterized by a loss of sensitivity for soft sounds, with little or no loss of sensitivity for intense sounds.
54
How does the number of channels affect frequency-specific audibility?
- Increasing the number of channels enhances the ability to restore frequency-specific audibility, especially for steeply sloping audiograms.
- The ideal range is between 9 and 18 channels. For flat or mildly sloping hearing loss, a 3-channel hearing aid can restore frequency-specific audibility.
55
what are the applications of compression?
1. Limit the output of the hearing aid without distortion,
2. Minimize loudness discomfort,
3. Prevent further damage to the auditory system,
4. Optimize the use of the residual dynamic range,
5. Restore normal loudness perception,
6. Maintain listening comfort,
7. Maximize speech recognition ability, and
8. Reduce the adverse effects of noise.
55
What is output compression limiting in hearing aids?
- Output compression limiting (OCL) uses compression to prevent the hearing aid's output from exceeding the LDL, avoiding distortion.
- It typically employs an output-controlled automatic gain control (AGC-O) circuit so that volume control adjustments do not affect the MPO.
55
What are the risks of intense sounds to hearing aid users?
- Intense sounds can force a hearing aid into saturation, causing distortion, amplify sounds beyond the individual's loudness discomfort levels (LDLs), leading to discomfort, and potentially cause amplification-induced hearing loss.
55
How can discomfort and damage from intense sounds be avoided in hearing aids?
- Discomfort and damage can be avoided by reducing the maximum power output (MPO) of the hearing aid.
- However, only compression effectively avoids distortion.
56
Why is AGC-O preferred over AGC-I for avoiding distortion, discomfort, and damage?
AGC-O is preferred because it ensures the MPO is set just below the LDL, regardless of volume control adjustments.
56
How does compression handle intense sounds differently between single- and multi-channel hearing aids?
- Single- and multi-channel compression can handle intense sounds similarly for inputs of 50 dBSPL.
- However, at 90 dBSPL, a multi-channel hearing aid might produce a higher output than a single-channel hearing aid, potentially exceeding the individual’s LDL.
- Output compression limiting helps manage this by adjusting the gain to prevent saturation and distortion.
57
What type of automatic gain control is used to achieve audibility and loudness for SNHL, and why?
AGC-I (input-controlled automatic gain control) is used to achieve audibility and loudness.
It allows adjustments to the volume control to increase or decrease the output based on individual needs, especially when average data (LDL) is used.
57
What settings are typically used for output compression limiting?
High Threshold Knee (TK): 80 dBSPL or greater.
High Compression Ratio (CR): Greater than 8:1 to prevent exceeding the LDL.
Fast Attack Time: 10 ms or less to minimize overshoot and limit the duration of exceeding the LDL.
Release Time: 100 ms or shorter, or adaptive release time, to ensure audibility of speech following a sudden intense sound.
58
What settings are used to make soft sounds audible in WDRC?
- Low TK: Set at or below 50 dBSPL to make soft sounds audible.
- Full Dynamic Range Compression (FDRC): TKs at 20 dBSPL aim to compress the entire range of environmental sounds into the residual dynamic range of the individual.
- Low CRs: 4:1 or less over a wider range of inputs.
59
How does Wide Dynamic Range Compression (WDRC) differ from compression limiting?
WDRC is like gentle braking when approaching a stop sign, providing a smoother adjustment of gain. Compression limiting is more abrupt, like screeching to a halt.
59
What are the recommended attack and release times for WDRC to maintain sound quality?
- Attack Times (AT): Slower than 100 ms.
- Release Times (RT): Slower than 2 seconds.
60
How does linear amplification with output compression limiting (OCL) differ from WDRC in terms of loudness perception?
- Linear Amplification with OCL: Provides a fixed amount of gain regardless of the input level, making all sounds louder by the same amount, maintaining the loudness growth function as in sensorineural hearing loss.
- WDRC: Creates a loudness growth curve similar to normal hearing, making soft sounds audible, moderate sounds comfortable, and intense sounds loud.
60
How does multichannel compression benefit those with severe slopes in their hearing loss?
Multichannel compression allows for more precise adjustments across different frequency ranges, accommodating the significant changes in loudness perception across the frequency spectrum.
61
Why might experienced linear hearing aid users object to WDRC?
Experienced linear users might object to WDRC because they are accustomed to intense sounds being too loud and soft sounds being inaudible, whereas WDRC changes this perception.
62
How does WDRC handle intense sounds compared to linear amplification with OCL?
WDRC causes the output to approach the LDL (Loudness Discomfort Level) more slowly, increasing comfort for intense sounds by avoiding abrupt loudness.
62
What is mid-level or comfort-controlled compression and its benefits?
- Mid-Level Compression: Provides desired loudness for moderate to intense inputs using AGC-I.
- TK Setting: Typically set to 60 or 70 dBSPL.
- Low CRs: Less than 4:1, acting over a wide range.
- Attack and Release Times: Slower attack times of around 100 ms and release times slower than 2 seconds are advised.
62
How does mid-level compression alleviate the primary disadvantage of WDRC?
Mid-level compression below the TK provides gain similar to linear amplification, which helps to reduce the likelihood of feedback resulting from more gain.
Above the TK, it reduces gain for intense sounds, maintaining listening comfort like WDRC.
63
How does Wide Dynamic Range Compression (WDRC) make conversational speech comfortable compared to linear amplification with OCL?
Both WDRC and linear amplification with OCL can make conversational speech comfortable, but WDRC achieves this while providing additional benefits such as better handling of intense and soft sounds.
63
Why is WDRC preferred for achieving multiple hearing goals compared to linear amplification with OCL?
WDRC is preferred because it provides a more dynamic and tailored response to various sound levels and frequencies, allowing it to address multiple aspects of hearing needs simultaneously, which is less feasible with linear amplification and OCL.
64
How does WDRC maximize speech intelligibility while maintaining listening comfort?
WDRC adjusts the gain for different levels of input sounds, making soft sounds audible and intense sounds comfortable, which helps to maintain speech intelligibility without compromising on comfort.
64
Can WDRC achieve multiple goals in a single fitting? Provide examples.
*Yes, WDRC can achieve multiple goals in a single fitting. For example, multichannel WDRC can:
- Optimize the use of the residual dynamic range.
- Normalize the perception of loudness.
- Maintain listening comfort.
- Maximize the intelligibility of speech.
- Reduce the adverse effects of noise.
65
What is the benefit of WDRC for soft sounds?
WDRC makes soft sounds audible, improving audibility in quieter environments, which is not as effectively managed by linear amplification with OCL.
