The -placebo- subjective evaluation method has been investigated for sighted in-situ testing of vehicle sound systems. The placebo method is designed to reduce or eliminate bias effects that may occur with typical sighted in situ subjective evaluations. With the placebo method, some modified program selections are added to the normal program sets that listeners are to evaluate. Program modifications can be made to one or more spectral, spatial, dynamic or temporal parameters. The listeners are instructed that the modified programs are randomly distributed in their program list, and the vehicle's sound system, the modified programs, or both can affect the judgments they make. Hypothetically, this should cause the listeners to focus on judging each program selection instead of the vehicle. The placebo method was compared statistically and functionally against blind and sighted in situ methods, and the results are given.:
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