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Hearing Technology > Static Aspects Of Compression > Flashcards

Static Aspects Of Compression Flashcards

1
Q

Goals of compression

A

To amplify the normal range of sounds and fit them into a restricted dynamic range

To prevent exposure to very loud sounds without the distortion caused by peak clipping

To alter the short term intensity relationships between speech sounds in order to promote speech intelligibility

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2
Q

What is kneepoint?

A

When of compression; at what input compression kicks in

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3
Q

Hard kneepoint

A

Sharp kneepoint as hearing aid abruptly goes into the desired level of compression

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4
Q

Soft kneepoint

A

Curvilinear compression

Hearing aid achieves the desired level of compression gradually as input intensity increases

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5
Q

Compression ratio

A

How much of compression

Input:output

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6
Q

What is AGC

A

Compression change the gain on the hearing aid based on intensity of input

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7
Q

Two types of compression

A

AGC OUTPUT

AGC INPUT

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8
Q

Output compression configuration of hearing aid

A

MIC➡️VC➡️Amp➡️Rec

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9
Q

Volume control effects of AGCo

A

VC affects kneepoint and gain but not MPO

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10
Q

How can you tell a hearing aid is AGCo by listening to it

A

When you talk loudly volume will not change once it reaches the MPO

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11
Q

AGCo is associated with low power aids

A

False

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12
Q

Input compression configuration of aid

A

Mic➡️amp➡️VC➡️REC

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13
Q

AGCi is associated with

A

Lower power aids
TK control
WDRC

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14
Q

Uses of AGCi

A

Mild to moderate hearing losses have a greater dynamic range to work with, where varying MPO will not result in intolerable or damaging loudness

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15
Q

Effects of AGCi

A

Soft - volume goes up and down because gain is affected by the VC
Loudly - volume does not change because MPO is not affected by the VC

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16
Q

Two types of controls for altering compression kneepoint

A

Conventional compression control
Threshold kneepoint control

Controlled by clinician

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17
Q

Conventional compression control

A

Adjusts compression kneepoint Threshold by altering amount of voltage required before compression kicks in
When control is turned to max compressor requires a higher voltage to begin compressing, so kneepoint is raised along with MPO
At max kneepoint, aid is linear for a wider range of sounds
Used to set MPO on AGCo aids
Useful for clients with severe hearing losses and very restricted dynamic ranges

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18
Q

Threshold kneepoint control

A

Affects gain for soft sounds
Affects KP of compression for soft sounds, usually between 45 and 50 dB
Linear gain below kneepoint
Acts as gain booster for soft sounds
MPO not affected
As control is increased, gain for low intensity sounds is decreased
Right most line - gain is lowest and TK is set at the highest kneepoint
Left-most line - where gain is the highest and TK is set in the lowest kneepoint position

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19
Q

Compression ratio for output limiting compression

A

High kneepoint and a high compression ratio
Greater than 60 dB
5:1 or greater

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20
Q

Output limiting compression

A

Linear for most inputs, up to kneepoint
Then strong compression kicks in to limit output or MPO
Uses a high compression ratio to limit output instead of peak clipping, resulting in less harmonic distortion
Associated with powerful aids

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21
Q

WDRC

A

Wide dynamic range compression
AGCi
Low kneepoint and low compression ratios

60 dB or less
4:1 or less
Provides weak compress for a wide range of input intensities

22
Q

What kind of hearing loss WDRC

A

Mild to moderate sensorineural hearing loss

Normal loudness growth is more easily achieved using WDRC than with output limiting compression

23
Q

Frequency response graphs

A

Used to show gain provided to different intensity inputs across frequencies for WDRC
Does not work for output limiting compression as all inputs are given the same linear gain and until MPO is reached

24
Q

Two types of WDRC

A

BILL and TILL

25
Q

BILL

A

Bass increase at low levels

BILL compressed loud low frequency sounds more than quiet low frequency sounds but does not affect the highs

26
Q

TILL

A

treble increase at low levels

27
Q

Kneepoint for BILL

A

Lower for low than high frequencies
Low frequency sounds do not need to be very intense to trigger compression
The louder the low frequency the more it is compressed

28
Q

What is the purpose of BILL

A

Designed to reduce the upward spread of masking while retaining the intensity of high frequencies for consonants
Leads to better speech intelligibility in background noise

29
Q

Kneepoint for TILL

A

Low kneepoint for high frequencies
Takes less sound intensity for a high frequency input to go into compression than for low
Hearing aid will not compress soft high pitched sounds and therefore provides maximum gain for soft high pitched sounds

30
Q

What is TILL used for?

A

Clients who have a high frequency loss and hence a reduced range in high frequencies

Emphasizes soft high frequency consonants for clients with high frequency hearing loss

31
Q

Severe to profound heat loss

A

Output compression
Output limiting compression
Conventional compression control

32
Q

Clinical application of output compression

A

VC will change kneepoint and affect gain, will not increase MPO

Protects residual hearing and client comfort

33
Q

Clinical application for output limiting compression

A

High kneepoint and high compression ratio so high intensity outputs are highly compressed whereas soft and medium inputs are maximally amplified
Uses as much as possible of the client’s restricted dynamic range

34
Q

Mild to moderate hearing loss

A

Input compression
WDRC
TK control

35
Q

Clinical application for input compression

A

VC doesn’t affect kneepoint but adjusts both gain and MPO

Allows client to adjust both gain and MPO since they have a large dynamic range to work with

36
Q

Clinical application of WDRC

A

Low kneepoint, low compression ratio, linear gain provided for very soft sounds and less gain for more intense inputs. Slowly brakes input so output does exceed UCL

Provides different amounts of compression at different frequencies, depending on the configuration of the hearing loss so deals with sloping losses well

37
Q

Clinical application for TK control

A

Attempt to mimic OHC function. Changes kneepoint and hence gain for soft inputs

38
Q

What is the benefit ofTK control

A

Lower kneepoint provides max gain for soft consonant sound
May raise kneepoint to reduce gain for soft sounds if the client thresholds if 40 dB HL or less, so hearing aid component sounds are not audible to the client
Can use expansion to reduce the audibility if the hissing if the components

39
Q

Clinician control effects for AGCo

A

Conventional compression control

40
Q

Conventional compression control

A

Adjusts compression kneepoint used to set MPO (dB SPL - 15 dB greater than UCL)

41
Q

Conventional compression control affects ______________ and ______________ but not _____________

A

Kneepoint, output (MPO) but not gain

42
Q

AGCo is associated with ____________ kneepoint and ____________ compression ratio

A

High - greater than 60 dB SPL

High - 5:1 or greater

43
Q

Who is AGCo appropriate for?

A

Severe to profound HL

44
Q

AGCi volume control effects

A

Gain and MPO but not kneepoint

45
Q

How can you distinguish a AGCi by listening to it

A

When you talk loudly volume will change at the max due to changing MPO

46
Q

Clinician control effects for AGCi

A

Threshold kneepoint compression

47
Q

TK affects ____ and _____ but not _____

A

KP
gain
MPO

48
Q

What does increasing TK control result in

A

More gain for very soft sounds under 40 dB so the client is less bothered by component sounds

49
Q

What clients would use AGCi?

A

Mild to moderate hearing losses thus varying MPO will not result in intolerable loudness

50
Q

With respect to AGCi and AGCo what is used today

A

Usually use AGCi for softer inputs and AGCo for louder inputs

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