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[[Image:Inside the Yamaha SY77.jpg|thumb|300px|The inside of a [[Yamaha SY77]] synthesizer shows the various internal components. The switches for each key are connected to the microprocessor chip using a matrix circuit. Even though the SY77 has 61 keys, only a small ribbon cable of wiring comes from the keyboard. ]]
There are at least two limitations with this system. The first is that it provides only a crude binary on/off signal for each key. Better electronic keyboards employ two sets of switches for each key that are slightly offset. By determining the timing between the activation of the first and second switches, the velocity of a key press can be determined — greatly improving the performance dynamic of a keyboard. ▼
The second is that instruments with a matrix circuit can only play in a [[monophony|monophonic]] fashion without the addition of a diode for each key crossing<ref>Jim Cairns, "Keyboard Encoders" http://www.jimspage.co.nz/encoders.htm</ref>. The [[diode]] is a one-way valve which prevents unwanted notes ("phantom keys") from being triggered, or intended notes from being masked ([[Keyboard (computing)#Control_processor|"phantom key blocking"]]).<ref name="dribin" />▼
Monophonic instruments and most low-cost computer keyboards reduce costs by leaving out most or all of those diodes.▼
To avoid "phantom keys", the keyboard controller in modern low-cost computer keyboards will ignore further key presses once two keys (other than [[modifier key]]s) have been pressed down, which is known as [[rollover (key)#Key jamming and ghosting | jamming]].▼
The matrix circuit approach used in musical keyboards is also used in other types of non-musical keyboards, such as in the keypads for calculators and the "QWERTY" alphabetic and numeric keyboards used to enter information into computers.<ref>
Jeff Tyson and Tracy V. Wilson.
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[http://webpages.charter.net/coinopcauldron/swarticle.html "Understanding the Switch Matrix"]
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▲There are at least two limitations with this system. The first is that it provides only a crude binary on/off signal for each key. Better electronic keyboards employ two sets of switches for each key that are slightly offset. By determining the timing between the activation of the first and second switches, the velocity of a key press can be determined — greatly improving the performance dynamic of a keyboard.
▲The second is that instruments with a matrix circuit can only play in a [[monophony|monophonic]] fashion without the addition of a diode for each key crossing<ref>Jim Cairns, "Keyboard Encoders" http://www.jimspage.co.nz/encoders.htm</ref>. The [[diode]] is a one-way valve which prevents unwanted notes ("phantom keys") from being triggered, or intended notes from being masked ([[Keyboard (computing)#Control_processor|"phantom key blocking"]]).<ref name="dribin" />
▲Monophonic instruments and most low-cost computer keyboards reduce costs by leaving out most or all of those diodes.
▲To avoid "phantom keys", the keyboard controller in modern low-cost computer keyboards will ignore further key presses once two keys (other than [[modifier key]]s) have been pressed down, which is known as [[rollover (key)#Key jamming and ghosting | jamming]].
==References==
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