This rain sound effects generator circuit simulates the rain noise and may be used in the field of electronic music and radio shows.
As a noise source we use a germanium diode that is directly polarized then is amplifier by a single stage amplifier in order to obtain an acceptable audio level.
A high-pass filter with an adjustable lower limit, built with P1 and C3, allow coverage of the entire range of sound effects from light rain and to torrential rain.
The current consumption is low so you can use a 9V battery. Instead of BC107 you can use any NPN transistor.