Smiley face curve
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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 didn't 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. 
Certain styles of electric bass playing, especially slapping, tend to augment the midrange frequencies. Various compensations have been developed to counteract excess midrange response in the instrument, including the use of amplifiers with a built-in smiley face curve and amplifiers that offer a handful of graphic equalizer filters so that the user can make the necessary adjustments when appropriate.
Gallien-Krueger makes an instrument amplifier that produces a classic smiley face curve in its default voicing. However, it includes tone controls that can be adjusted so that the amplifier is within 0.5 dB of a neutral, uncolored frequency response.
Some bass players decry the attenuation of midrange frequencies, holding that the midrange area centered on 500 Hz will make the bass instrumental line stand out more satisfyingly in the mix. University of Iowa professor and bass player Dan Berkowitz has observed that the smiley face curve as applied to bass played within a blues or R&B band can make it hard for bandmates to play off the bass line. Berkowitz recommends an upside down smile curve: a "frown" curve with its peak centered at 500–800 Hz.
Guitarists and bassists can choose to equalize their instrument with an effects pedal. Several products exist for this purpose such as a 10-band MXR-branded equalizer offered by Dunlop Manufacturing which includes instructions for a "Metal Distortion" setting that reduces 1,000 Hz, a midrange frequency, down to its maximum reduction point, with nearby frequencies reduced in the form of a mid scoop.
Live sound reinforcement
Some concert sound mixers employ the smiley face curve as a tool to help them gain initial control of a sound system. Even with recorded sound, the smiley face curve has its backers. Will Shapland of Floating Earth location recorders said in 2004 that his basic mixing technique for the recordings of the Isle of Wight Festival was to use "a bit of a 'smiley-face' EQ curve on the output" until he got a handle on a new band's mix, at which point he said "your balance comes together and you don't really need it."
Kip Bradford of Expert Village emphasizes that the live sound engineer must not employ smiley face curves when setting up a sound reinforcement system. Bradford advises that the graphic equalizer should instead be used to "tune the system to the room", taking account of the combined frequency response of the room and the sound system to ensure that all audible frequencies have equal presence.
Some audio equipment manufacturers have accommodated the user by engineering a smiley face curve into a product. dbx, Inc. offers several smiley face curve presets in their digital graphic equalizer product line called DriveRack. Jim Dunlop offers a direct box intended for bass players that includes a preset labeled "color" which engages a smiley face curve. Neither of these products prevent the user from adjusting the equalizer based on the sound that is actually heard rather than relying on a predetermined visual image.
Alpine Electronics has offered for sale a product for car audio systems that works to counteract any smiley face curve that was applied to a car's factory OEM sound system, along with an analysis feature that adjusts for road and vehicle noise. Empeg Car, a digital media player, includes a "Loudness Control" feature that is described as adding a "smiley face" curve automatically" at low sound levels but which is used to lesser and lesser degrees as the car sound system's volume is increased. This describes an equal-loudness contour circuit.
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- Diverse Devices. Video and Audio Abbreviations and specialised terms
- Harmony Central Musician Community Forums. Recording Forum. "Smiley face" EQ curve... feelings? Posted by Elements6259 on March 18, 2004. "I see (non-recording) people do it on their cars and stereos all the time..."
- Media College. Audio Forum. Getting Rid of Feedback. Post by fstfwd74 on September 8, 2007. "My biased perception ...is much the same as seeing a soundman's eq set to "smiley face" setup... it's an indicator of inexperience or maybe last resort..."
- ActiveBass: The Online Bass Community. November 7, 2002. Kelly Marsh. How to EQ Your PA
- Ampage.com. Tube Amps / Music Electronics. Archive of vintage threads from the first ten years. Re: Settings for Peavey XR600F. Posted by Enzo on October 15, 2004. "Some folks even tell you to set the smiley face before you even turn it on."
- Slashdot.org. Why Music Really Is Getting Louder: Not always true – the Fletcher-Munson curve. Post by Andy R on June 9, 2007. "The 'smiley face' EQ curve is actually desirable if you are listening at lower than usual volume levels."
- Audioholics: Online A/V Magazine. Home Theater Forums. EQ Horse Hockey?. Post by Rob Babcock, Moderator, on June 6, 2004. "Pretty much everyone tried to boost the lows to get some decent bass and boost the treble to try to coax something resembling highs out of the 2" paper tweeter!"
- Car Audio Book. Car Audio Basics. What Is Sound?
- Electronic Musician. December 1, 2007. Brian Smithers. Square One: The Sculptor's Tool: How to use EQ to shape your music
- Car Audio Book. Car Audio Basics. Car Audio Signal Processors – Crossover, Equalizers and More
- Basic Car Audio Electronics. Graphic Equalizers
- Francis Deck. December 22, 2005. GK Backline 600 Review
- Ernie Ball. Forums. Music Man Basses. Need Some Effects For My New Bongo Post by adouglas on September 26, 2008. "Keep it pure, keep it clean, EQ it right (mids are your friend, avoid "smiley face" EQ curves) and let your fingers do the talking."
- Premier Guitar. September 2008. Mike Visceglia. Zen & the Art of Bass Tone "...Ivan Bodley, bassist for soul legend Sam Moore... said that if you invert the normal smiley-face EQ curve to a frown-face curve with 500Hz as the high point, you generally will have a tone that cuts through most live band performances."
- Premier Guitar. March 2008. Dan Berkowitz. Bass EQ Basics: A frown for the smiley face. "It sounds big and powerful, but lacks the note definition that helps your bandmates play off of what you’ve done on bass."
- Jim Dunlop. MXR M-108 Ten Band Graphic EQ (PDF image manual)
- Sound On Sound. December 2004. Daniel James. Live Sound. The Isle Of Wight Festival Sound: Behind The Scenes
- Expert Village Presents. Music series. Kip Bradford. How to Set Up PA Systems: 11. How to Set Up a Graphic Equalizer. (online video)
- dbx, Inc. Studio DriveRack Manual. pp. 38. Presets 9, 13 and 17.
- Sputnik Music. Forums. MXR M-80 Bass DI+. Post by edgebass5 on September 19, 2005. "Essentially all the color switch does is engage a preset "smiley face" EQ curve."
- engadget.com. Darren Murph. January 14, 2008. Alpine adds brains to in-car equalization with IMPRINT architecture
- Persiconi Construction. WRX. Downloads. Empeg Sound