more theory

Question 1

Why is compression useful?

Answer 1

• Optimises DR (ensures all sounds fit in person’s DR)
• Maintains listening comfort (ensures loud sounds are not uncomfortable)
• Maximises speech intelligibility (ensuring different aspects of speech is audible)
• Reduces adverse affects of noise on speech intelligibility (expansion, compression in the LFs - where BGN generally is)

Question 2

What is the game formula?

Answer 2

Gain (DB) = output (dB SPL) - imput (dB SPL)

Question 3

Why are input/output graphs useful?

Answer 3

Tells us exactly what the hearing aid is doing, whether a linear amplification or compression
Can also determine how much gain is being applied (gain graphs)

Question 4

Compression ratio equation

Answer 4

CR = change (∆) in input divided by change (∆) in output

Higher the CR - more compression there is - and line becomes more horizontal (input/output graph)

Question 5

What are the benefits of having a high compression ratio/CT?

Answer 5

Increase the clients here and comfort because I’m not hitting the limit quickly. Can slow down and he’s allowed to sounds for longer.

Question 6

What are the benefits of having a high compression ratio/CT?

Answer 6

Increase the clients here and comfort because I’m not hitting the limit quickly.

• Safety of Pt hearing
• Can slow down and he’s allowed to sounds for longer.
• Does not impact thresholds below the CT, thus gain remains the same - typically linear
• Less need for volume control adjustment (loud sounds not becoming too loud when exposed to loud sounds)

Question 7

What are the benefits of having a low compression ratio/CT?

Answer 7

Increased audibility and therefore speech intelligibility. Because allowing more room to amplify more of the softer sounds before it reaches the hearing aid limit.
- Does not overamplify - thus increased comfort

Question 8

What are the limitations of having a low compression threshold?

Answer 8

Increased risk of feedback, increased risk of internal hearing a noise, increased risk of amplification of background noises such as fridge coming or clock ticking

Question 9

Why are use expansion?

Answer 9

Essentially used to reduce soft annoying sound such as the fridge coming. Typically used for low-level imports to reduce the gain as the input increases