“This article describes a simple device based on an ATtiny85 that takes an audio input, shifts its pitch up or down in real time, and plays it through a loudspeaker. You can increase or decrease the pitch shift using two pushbuttons: For example, you can plug in an mp3 music player or phone, play some music, and change the pitch of a male singer’s voice to a female voice as it’s playing. Although the result is not hi-fi quality, it’s an excellent demonstration of how much you can achieve with a single ATtiny85. The chip first amplifies the input by a factor of x20, digitizes it, stores the samples in a circular buffer under interrupt, reads samples back from the circular buffer under a separate timer interrupt, and finally converts the processed digital signal back to analogue, using high-speed PWM, and outputs it to a loudspeaker. Two pushbuttons cause interrupts which change the pitch shift up or down.”