Module 8

Question 1

What is gain?

Answer 1

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

Question 2

What is frequency response?

Answer 2

The gain at various frequencies

Question 3

What is saturation response?

Answer 3

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

Question 4

What is input-output function?

Answer 4

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

Question 5

What is linear amplification?

Answer 5

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

Question 6

What is non-linear amplification?

Answer 6

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

Question 7

What are the main purposes of compression?

Answer 7

-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

Question 8

What is compression ratio?

Answer 8

-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

Question 9

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

Answer 9

TRUE

Question 10

What is compression limiting?

Answer 10

Occurs when the output does not exceed a set limit

Question 11

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

Answer 11

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

Question 12

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

Answer 12

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

Question 13

What is wide dynamic range compression?

Answer 13

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

Question 14

T/F: compression is instantaneous

Answer 14

FALSE: there is attack and release time

Question 15

Attack Time vs Release Time

Answer 15

-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

Question 16

What is headroom?

Answer 16

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

Question 17

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

Answer 17

-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

Question 18

What is expansion?

Answer 18

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

Question 19

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

Answer 19

TRUE