Module 8 Flashcards
What is gain?
-The difference between the input intensity (reaching the hearing aid microphone), and the output intensity (from the hearing aid receiver)
-Gain = Output - Input
What is frequency response?
The gain at various frequencies
What is saturation response?
Maximum output that the hearing aid can produce. In a saturation response, a higher input does NOT translate to a higher output
What is input-output function?
Visual representation of output as a function of input (the gain provided by the hearing aid will depend on the input level)
What is linear amplification?
The amount of gain applied is the same, regardless of the input (1:1 relationship)
What is non-linear amplification?
The amount of gain applied depends on the input (i.e., soft, moderate, or loud intensity sounds)
What are the main purposes of compression?
-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
What is compression ratio?
-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
T/F: compression can also be called non-linear gain
TRUE
What is compression limiting?
Occurs when the output does not exceed a set limit
Before compression was possible, what was used to limit the output on a hearing aid?
Peak Clipping: results in distortion, and a poor speech perception and degrades intelligibility
What is the Compression Threshold (CT) or Knee Point?
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
What is wide dynamic range compression?
WDRC is a compression activated across a wide range of inputs (i.e. a low knee-point or compression threshold)
T/F: compression is instantaneous
FALSE: there is attack and release time
Attack Time vs Release Time
-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