Smiley face curve

A smiley face curve (also known as "mid scoop") in audio signal processing, is a target frequency response curve characterized by boosted low and high frequencies coupled with reduced midrange frequency power. This curve is often attained by users employing a graphic equalizer which shows a graphic representation of a "smile" using its frequency band faders to describe a curve that sweeps upward at the left and right sides.

Smiley face curves have had a popular appeal with some car audio enthusiasts, disc jockeys, electric bass guitar players, home stereo owners and live sound reinforcement system operators. Though the graphic equalizer was intended to tailor a system's response to match existing venue and performance conditions, the smiley face curve is often applied before the user has heard the system's frequency response.

The smiley face curve is roughly analogous to the frequency response of human hearing as charted in the equal-loudness contour, and has been compared to loudness compensation circuitry in that it increases the relative power of high and low frequencies without increasing the midrange power. In order for a sound system to be heard properly by humans, it should have an equal-loudness contour applied to it when it is performing at low sound pressure levels, then the curve should gradually flatten out as it gets louder.

The origin of the smiley face curve has been attributed to the search for more bass and treble response from loudspeakers that did not extend as low or as high as desired, especially in the 1970s and 1980s. It has also been seen as either a useful or a detrimental tool for shaping the sound of a bass guitar.

Many cars which have a graphic equalizer have been observed to have it set as a smiley face curve which emphasizes low and high frequencies. Graphic equalizer use leading to speaker damage is common — large amounts of bass boost and treble boost can distort music and damage loudspeaker drivers. Ideally, the equalizer can be set once to compensate for the combination of the response of the speakers and the car's acoustic characteristics. A smiley face curve can indicate that a car's sound system is lacking both high and low frequency response.

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