Signal detecting circuit for electronic musical instrument

DETAILED DESCRIPTION What is claimed is: 1.
A signal detection circuit comprising: a first rectifier for rectifying an input signal of an audio frequency band; a first comparator for comparing the level of the output of said first rectifier with a reference level; a second rectifier for rectifying said input signal; an integrator for integrating the output of said second rectifier; a second comparator for comparing the level of said input signal with the level of the output of said integrator; means for delaying a response speed of the output of said second comparator; means having a threshold level for generating an output comparing the output of said delaying means with the threshold level; and a flip-flop circuit controlled in accordance with the outputs of said first comparator and said threshold level means for generating an output representing rise and fall of said input signal.
2.
A circuit according to claim 1, further comprising means for level-shifting one of said input signal level and said integrator output level before applied to said second comparator.
3.
A circuit according to claim 1, in which said delaying means comprises a capacitor having a discharging path and a charging path which has a time constant larger than that of the discharging path, said capacitor being charged and discharged in accordance with the output of said second comparator.
4.
A circuit according to claim, 1, in which said flip-flop circuit is an R-S flip-flop having two inputs respectively applied with the outputs of said first comparator and said threshold level means and an output in use for delivering said output representing rise and fall of said input signal.




Description:
BACKGROUND OF THE INVENTION This invention relates to a signal detecting circuit for an electronic musical instrument in which an acoustic vibration is picked up to generate an electrical signal which is used as the input signal to drive the electronic musical instrument.
An electronic musical instrument of this type, such as a so-called guitar synthesizer is provided with a function to trigger off a musical tone in accordance with the external vibration signal and a function to store and hold the external vibration signal (such as a string vibration signal) so that, even after the vibration of a string has been stopped, the musical tone can be produced