The invention relates to a method of establishing a harmony control signal controlled in real-time by a guitar audio input signal (GAS), comprising the steps of providing a first input harmony input control signal (FIH) on the basis of said guitar audio input signal (GAS), providing a second input harmony control signal (SIH) on the basis of a voice audio input signal (VAS). providing an input audio extraction representation (IAER) on the basis of said first input harmony input control signal (FIH), establishing a harmony control signal (HCS) on the basis of said input audio extraction representation (IAER) and said second input harmony control signal (SIH).