Module 8 Flashcards

1
Q

What is gain?

A

-The difference between the input intensity (reaching the hearing aid microphone), and the output intensity (from the hearing aid receiver)
-Gain = Output - Input

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2
Q

What is frequency response?

A

The gain at various frequencies

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3
Q

What is saturation response?

A

Maximum output that the hearing aid can produce. In a saturation response, a higher input does NOT translate to a higher output

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4
Q

What is input-output function?

A

Visual representation of output as a function of input (the gain provided by the hearing aid will depend on the input level)

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5
Q

What is linear amplification?

A

The amount of gain applied is the same, regardless of the input (1:1 relationship)

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6
Q

What is non-linear amplification?

A

The amount of gain applied depends on the input (i.e., soft, moderate, or loud intensity sounds)

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7
Q

What are the main purposes of compression?

A

-Compression helps to preserve the waveform and maintains speech recognition ability
-Maintains a perception of “soft”, “moderate”, and “loud” sounds by fitting the sound into the residual dynamic range
-Maintains a comfortable listening level for patients
-Reduces the adverse effects of loud inputs

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8
Q

What is compression ratio?

A

-The ratio of incremental change from input to output level
-How much does the input change to effect 1 dB change in the output?
-CR = ∆input/∆output

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9
Q

T/F: compression can also be called non-linear gain

A

TRUE

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10
Q

What is compression limiting?

A

Occurs when the output does not exceed a set limit

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11
Q

Before compression was possible, what was used to limit the output on a hearing aid?

A

Peak Clipping: results in distortion, and a poor speech perception and degrades intelligibility

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12
Q

What is the Compression Threshold (CT) or Knee Point?

A

The level set where compression will be activated. In an input/output graph, this is the “bend” deviating from the 45 degree (linear gain) angle

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13
Q

What is wide dynamic range compression?

A

WDRC is a compression activated across a wide range of inputs (i.e. a low knee-point or compression threshold)

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14
Q

T/F: compression is instantaneous

A

FALSE: there is attack and release time

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15
Q

Attack Time vs Release Time

A

-Attack Time: the time it takes to TURN DOWN the gain in response to an increase in the signal level. The attack times can vary (usually 1-20 ms)
-Release Time: the time it takes to TURN UP the gain in response to a decrease in the signal level. The release times can vary (20-30 ms up to approximately 5 seconds)
·Too fast: slight distortion and “pumping” may be audible
·Too slow: may be audibility gaps for patients

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16
Q

What is headroom?

A

The dB range between the upper level of amplified speech and the hearing aid’s Maximum Power Output (MPO)

17
Q

What are the two types of Automatic Gain Control (AGC)?

A

-AGCi: input controlled compression systems detect the level input before the volume control of the hearing aid. The gain is reduced at the pre-amplifier of the hearing aid
-AGCo: output controlled compression systems detect the level input after the volume control of the hearing aid. The gain is reduced at the output amplifier of the hearing aid

18
Q

What is expansion?

A

A technique used in hearing aids to make low level sounds softer (e.g., environmental sounds)

19
Q

T/F: expansion (like compression) can have a kneepoint, attack and release times, and a ratio

A

TRUE