The acquired stereo voltage signal was split into left and right data streams within the Labview programming environment. Each stream was then directed to a user-selectable and adjustable (via the graphical user interface of the designed Labview program) ten-band equalizer.
The equalizer was based on a frequency band selection principle whereby the data stream was multi-replicated, with each replication (one for each band) separately fed to a third order Butterworth bandpass selection filter.
The gain-controlled outputs of all filters were then recombined for the left and right streams. The default frequency cut-off limits for the ten bands were 6000 Hz.
These default band limits were additionally adjustable to suit the audiometric response of the user. The equalization (multiband gain control) approach was an expansion of a three band, single stream approach21 applied to the iPhone.
All bands for the present study allowed for a user-adjustable gain from 0 to 40 dB, except for the lowest two bands which had an extended gain range of -20 to 40 dB.