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0611 RM500SL User’s Guide Version 2.8 Page 71
17.3 DSL 5.0 in Speechmap
FastFacts 17.3: DSL 5.0 in Speechmap
The
Desired Sensation Level (DSL)
method is a systema
tic eardrum sound
pressure level (SPLogram) approach to hearing instrument fitting that seeks to
ensure amplified speech will be audible and comfortable while loud sounds will not
be uncomfortable. It takes into account individual acoustic factors in audiometric
and electroacoustic data. DSL was developed by the National Centre for
Audiology (NCA), London, Ontario. Audioscan has implemented DSL within its
Speechmap fitting system since 1994.
In 2005, DSL underwent an extensive revision. This has resulted in changes to
speech targets for children. These changes will be more significant when the
individual RECD values have not been measured for the child being fitted. See
17.4:DSL 5.0 changes and www.audioscan.com for details of the changes.
The Audioscan version of DSL 5.0 may differ from others in the following ways:
1) DSL 5.0 uses RECD values for ages > 119 months from a different source than
for ages ≤ 119 months; Audioscan has used the RECD values for a 119 month
old for ages > 119 months so all values come from the same study.
2) Input-output curve targets and compression threshold targets are not provided.
Such steady-state parameters are of little value in estimating amplified speech
levels. Matching amplified speech to the LTASS targets at levels from 50 to 75
dB SPL provides much better assurance that fitting goals are being met.
3) There is no provision to input the number of compression channels. This may
be useful when the signal used for verification is not the signal for which the
targets were developed. It is irrelevant when using real-
speech signals to match
speech targets and when using narrow-band signals to match narrow-band
maximum output targets.
4) The term Uncomfortable Level (UCL) is used rather than Upper Limit of
Comfort (ULC) in referring to the ear canal SPL that should never be exceeded.
5) Broadband output limiting targets are not provided.