Debra Audio D-440 4 channel wireless microphone system.There series products adopt UHF frequency and use the international standard common frequency which can be used in all over the world. Due to the low frequency and many reasons, traditional wireless any digital equipments. Squelch circuit usually analyzes the intensity of the RF frequency channel instead of the noise and the needed signal. Using the low traditional wireless microphone in the complex environment or when the signal of the microphone is week or the microphone is closed, the squelch circuit many suddenly opened which result the receiver sending out a strong burst of noise. Do not change the frequency when using one set system.It ideal for church, small DJ KJ stage, birthday wedding or family party,conference, classrooms, small karaoke night etc.