FONIX® 8000 - Frye Electronics

192 FONIX 8000 Hearing Aid Analyzer
With the 8000, we offer an additional option for the speech peak: the actual
measured peak. Since we are recording and analyzing 10 ms time slices of
speech, we may be reasonably confident of capturing plosives and accurately
capturing the actual peak SPL of a speech sample.
implementation:
SII is implemented in the Visible Speech screen of the 8000. Within this screen,
the user has a menu choice of using the measured peak for speech peaks, or
using the measured average plus 12 dB, or using the measured average plus 15
dB. Pre-existing logic within the 8000 converts the entered audiogram into the
perception threshold (the HTL values expressed in SPL).
Once speech peak values are available (which generally means once measurement
has been started), for each plotted frequency, the difference between the
speech peak and the HTL is taken, trimmed to the 0-30dB range, and scaled by
the weighting factor for the range. The resultant values are summed, and then
result is scaled to the appropriate 0-100 range. This resulting SII value is displayed
in the curve characteristics box in the rightmost column.
The frequency weights used were derived from values given in “Derivation of
primary parameters and procedures for use in speech intelligibility predictions”,
Chaslav V. Pavlovic, J. Acouts. Soc. Am 82(2), August 1987. These weights are
obtainable from the 8000 via RS232 using the Get List command when in the
Visible Speech major mode. The frequencies used for the frequency bins are
obtainable via the same command. The Set List command may be used to send
arbitrary weights to the instrument for use in SII calculation. When the weights
in use differ from those supplied by default, an asterisk (*) appears next to the
SII value on screen.
For calculating SII values for targets, each target is treated as if it were the mean
value of a speech envelope. When peaks are set as mean+12 dB or mean+15
dB, target peaks are similarly calculated as target+12 dB or target+15 dB. When
the speech peak is set as the measured peak, the target peak is calculated as the
target plus the difference between the measured peak and the measured mean.
In other words, if the entire measured envelope were shifted in each frequency
band, up or down as necessary, until the measured mean was right on the target,
the shifted measured peak would define the values used for the target peak.
Otherwise, the SII measurement proceeds in the same manner as for a measured
envelope.
Settings:
The following settings are available in the Visible Speech local menu. You can
reach the local menu by pressing [MENU] while in the Visible Speech screen.
• Noise Reduction (Comp): 0, 2X, 4X, 8X, 16X. This determines how much
averaging the real-time measurement curve does while the test is running.
Larger numbers do more averaging. Lower numbers do less.