Frequency-weighted ®lter Sample Clauses

Frequency-weighted ®lter. A frequency-weighted angle ®lter weighs postural signals by the corresponding frequency in proportion to the equal discomfort function, so that the ®ltered angular data accounts for the relative discomfort associated with motion and repetition. The attenuation slope for the frequency- weighted angle ®lter is determined by the relative relationship between angle and repetition and can be obtained by algebraically solving the discomfort model at a given exertion and discomfort level. Similarly, a frequency-weighted force ®lter weighs force signals by the corresponding frequency in proportion to the equal discomfort function and its attenuation slope can be determined by solving the discomfort model at given angle and discomfort level. Based on the discomfort model developed, the attenuation slope is 24 dB/decade for the frequency-weighted angle ®lter and 14 dB/decade for the frequency-weighted force ®lter. The frequency-weighted angle ®lter was modelled using MATLABT M (The MathWorks Inc., Natick, MA, USA) as a ®nite impulse response (FIR) high-pass ®lter with a 24 dB/decade attenuation slope in the linear region. The diSerence equation for the FIR ®lter is: XF ( nT) 5 k50 bk X( nT 2 kT) where XF (nT ) is the output associated with the current sample time nT , and X(nT — kT) is the input value, k sample points in the past. The output value XF (nT) of the frequency-weighted ®lter is the weighted sum of the input for the current sample, X(nT ), and the input values for the preceding N samples. CoeScients for the resulting diSerence equation are listed in table 5. The characteristics of the frequency-weighted angle ®lter are illustrated in ®gure 5. The cut-oS frequency for k bk 0 0×0016 1 0×0015 2 0×0012 3 — 0×0000 4 — 0×0031 5 — 0×0089 6 — 0×0179 7 — 0×0301 8 — 0×0448 9 — 0×0607 10 — 0×0760 11 — 0×0888 12 — 0×0972 13 0×9015 14 — 0×0972 15 — 0×0888 16 — 0×0760 17 — 0×0607 18 — 0×0448 19 — 0×0301 20 — 0×0179 21 — 0×0089 22 — 0×0031 23 — 0×0000 24 0×0012 25 0×0015 26 0×0016 this ®lter was arbitrarily set at 1 Hz because of limitations in the ®lter design algorithm that was constrained by the attenuation slope and the desired bandwidth. The details for determining the attenuation slope for frequency-weighted ®lters are discussed in ▇▇▇ et al. (1997).