In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of systems, such as audio and control systems, where they simplify mathematical analysis by converting governing differential equations into algebraic equations. In an audio system, it may be used to minimize audible distortion by designing components so that the overall response is as flat (uniform) as possible across the system's bandwidth. In control systems, such as a vehicle's cruise control, it may be used to assess system stability, often through the use of Bode plots. Systems with a specific frequency response can be designed using analog and digital filters.

किसी तंत्र (सिस्टम) के इनपुट की आवृत्ति बदलने पर उसके आउटपुट का परिमाण (मैग्निट्यूड) एवं फेज के परिवर्तन को उस तंत्र की आवृत्ति अनुक्रिया कहते हैं। आवृत्ति अनुक्रिया उस तंत्र की गतिक विशेषता बताती है। इसका नियन्त्रण तंत्र के डिजाइन में बहुत उपयोग होता है।