The ornamental design for an audio signalprocessor, as shown and described.
FIG. 1 is a perspective view of the front, top and right side of an audio signal processor showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof,
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom view thereof.
The broken line showing of the audio signal processor is included for the purpose of illustrating unclaimed portions of the audio signal processor and forms no part of the claimed design.