An electrical signal processing system, including an acoustic wave filter having a desired frequency response including a passband, a predetermined pass band loss, a stop band, and a predetermined minimum stop band attenuation by a predetermined frequency, wherein: the filter comprises a first acoustic wave module, a second acoustic wave module (214A, 214B), and first variable capacitor module; the first acoustic wave module and the second acoustic wave module (214A, 214B) each comprise acoustic wave resonators (292B; 214A, 214B); the first acoustic wave module filters electrical signals and has a pass band and a stop band (263, 304A), and the stopband edge varies due to temperature and process variations; the second acoustic wave module (214A, 214B), being serially coupled to the first acoustic wave module, filters electrical signals and has a desirable passband and an undesirable passband with a stopband in between; the stopband (263, 304A) of the first acoustic wave module suppresses the undesirable pass band of the second acoustic wave module (214A, 214B); the first variable capacitor module has a plurality of capacitances selectable via a first control line and is coupled in parallel to the second acoustic wave module (214A, 214B); and the first variable capacitor module variably modifies the frequency of the stopband of the second acoustic wave module (214A, 214B) to compensate for variations in the stopband edge of the first acoustic wave module; whereby the combined frequency response of the first acoustic wave module, second acoustic wave module (214A, 214B) and first variable capacitor module corresponds to the desired frequency response with a stable stopband having the predetermined minimum stop band attenuation by the predetermined frequency without temperature and process variations. the filter comprises a first acoustic wave module, a second acoustic wave module (214A, 214B), and first variable capacitor module; the first acoustic wave module and the second acoustic wave module (214A, 214B) each comprise acoustic wave resonators (292B; 214A, 214B); the first acoustic wave module filters electrical signals and has a pass band and a stop band (263, 304A), and the stopband edge varies due to temperature and process variations; the second acoustic wave module (214A, 214B), being serially coupled to the first acoustic wave module, filters electrical signals and has a desirable passband and an undesirable passband with a stopband in between; the stopband (263, 304A) of the first acoustic wave module suppresses the undesirable pass band of the second acoustic wave module (214A, 214B); the first variable capacitor module has a plurality of capacitances selectable via a first control line and is coupled in parallel to the second acoustic wave module (214A, 214B); and the first variable capacitor module variably modifies the frequency of the stopband of the second acoustic wave module (214A, 214B) to compensate for variations in the stopband edge of the first acoustic wave module; whereby the combined frequency response of the first acoustic wave module, second acoustic wave module (214A, 214B) and first variable capacitor module corresponds to the desired frequency response with a stable stopband having the predetermined minimum stop band attenuation by the predetermined frequency without temperature and process variations.