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23 Cards in this Set

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reasons to use compression

  • reduced dynamic range due to recruitment
  • provide more input levels within this dynamic range
  • listening comfort (not to exceed UCL/LDSs)
  • maximize intelligibility
  • control output without distortion

What is compression for high level sounds?

high gain for high level sounds

POOR COMPRESSION CAN ALTER TEMPORAL ENVELOPE OF SPEECH SIGNAL

memorize that

effects of compression

choices of compression speed

  • syllabic compression
  • automatic volume control

automatic volume control

  • AVC has slower acting time constraints
  • therefore, when impulses sound activates compression, significant time elapses until gain levels return to prior level
  • can reduce intelligibility of talker

compression alters the envelope



fast acting compression has more dramatic effect in temporal envelope

major advantages of AVC

less distortion of the temporal envelope of speech

major disadvantage of AVC

may render speech signal following compression inaudible due to longer release time

syllabic compression

fast acting compression that attempts to compress at the syllabic level (fast attack and release times)

When does syllabic compression attempt to compress and release?

before next portion of speech signal

advantages of fast acting compression

applies compression and release quickly to allow listener opportunity to perceive following phoneme



attempts to compress at the syllabic level



better for utilizing TFS of speech for dip listening

disadvantages of fast acting multi-channel compression

distorts the temporal envelope



unknown what the optimal number of channels should be



bor, souza found reduced vowel identification with multichannel compression

bor, souza, and wright took vowel signals, processed then through different compression mechanisms and found what?

in uncompressed, you could see spectral contrasts



as compression increased, spectral contrast decreased as well as vowel identification

dip listening

the ability to utilize the information in fluctuating background noise

dip listening and temporal fine structure

allows the listener to define properties of target speech

cochlear hearing loss of a moderate degree can (reduce/increase) ability to listen in dips

reduce

What type of compression system would be most beneficial for dip listening and why?

AVC because it is fast acting

What determines the type of compression that would be most effective?

the hearing impaired listener's ability to use TFS

compression for severe-to-profound SNHL

traditionally, individuals with this HL were typically fit with linear, output limiting instruments



listeners became accustomed to reduced bandwidth signals, increased amplified noise, and more distortion with output limiting devices



souza suggests that amplitude compression needs to preserve, as much as possible, the natural amplitude variations in speech (temporal envelope)

3 has the highest EDI (envelope difference index)

What can you do due to the gain for soft sounds (including environmental sounds) with WDRC

counsel, expansion

expansion

reduces gain as input decreases, below the TK