Appeal 2007-0333
Application 09/966,802
First, Sakata’s coefficient migration is capable of switching at least
one filter on and off. Our discussion of Sakata’s ability to disengage and
engage respective filters via changing cutoff frequency applies equally here
and we incorporate that discussion by reference.2
Second, Sakata’s engaging and disengaging filters is, in our view,
capable of being inaudible. As Sakata indicates, noise results from instantly
changing filter coefficients from one cutoff frequency to another (Sakata,
col. 1, ll. 33-40). Sakata then describes a previously-known filter coefficient
interpolation technique designed to avoid noise, but which produced
excessive deviations from the desired filter coefficient values. These
deviations ultimately produced unnaturally-sounding transient tones (Sakata,
col. 1, ll. 41-58). Sakata’s digital filter, however, smoothly changes the
cutoff frequency while substantially maintaining filter characteristics in a
region near the cutoff frequency -- even in response to large changes in
cutoff frequency (Sakata, col. 2, ll. 27-33). To this end, Sakata gradually
changes the goal value of cutoff frequency and interpolates corresponding
filter coefficients at each goal value (Sakata, col. 2, l. 65 – col. 3, l. 5; col. 4,
l. 51 – col. 5, l. 8).
The clear import of this discussion is that Sakata’s filter is designed to
prevent such problems in prior art filters, namely to avoid noise and transient
tones when filter coefficients are changed. Given this designed capability of
Sakata’s filter, we conclude Sakata’s filter is capable of switching inaudibly
as claimed given the scope and breadth of the limitation. Significantly, the
term “inaudibly” is extremely broad and somewhat subjective. Given the
2 See P. 4-6, supra, of this opinion.
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