To get the most enjoyment from your stereo speakers, your amplifier and your microphone, they must accurately reproduce sound frequency. The manufacturer of your stereo components will often use a frequency response curve to determine bandwidth and the upper and lower frequency limits of specific components to assure the quality of sound reproduction based on the visual results of a system's response to frequency input.
The frequency response curve is a visual representation of the quality of amplitude over frequency generated by specific components. The graph depicting such curve will have a vertical axis and a horizontal axis. The vertical axis is usually labeled as the level of sound, also called amplitude, in decibels (dB), while the horizontal axis is labeled as the frequency, the vibration that is captured by your ear and is measured in hertz (Hz).
Frequency is the number of sound waves that pass a fixed receptor, your ear for example, in an established amount of time. This may also be called a cycle. A circuit response is also a measure represented by a frequency response curve. It is a determination of how well the circuitry of your individual components handles the constant variations in frequency at specific and constantly maintained amplitudes.
Bandwidth is the boundary or band marking the highest frequency signal output to the lowest demonstrated by a particular component. The fo in a frequency response curve is the peak of the curve, where the actual bandwidth is noted and compared to the designed bandwidth of the component. Should the actual bandwidth not measure up to the design, the frequency response of the component can be improved using a digital or analog filter.
A hi-fidelity amplifier usually has a frequency response of 20 Hz to 20,000 Hz within approximately one dB. The human ear can normally detect audio frequencies encompassed by that specific range with a dB being the loudness or amplitude. The system should be able to amplify all the frequencies in that range.
The specific numbers indicated by the frequency response curve are not as important as the variation of response from frequency to frequency (e.g. high frequency to low frequency and vice versa). Acceptable frequency response doesn't mean accurate sound reproduction, only that the tested component meets basic frequency response requirements. This response indicates to the tester that the component will accept an input signal and generate a response. The frequency response curve will not, however, define the actual audio quality.