The most significant difference between single and double system recording is where the audio sound is recorded from. In a double system recording, the images and the sound are recorded in two different devices. Sound is recorded on the first device, and the picture and the reference audio is recorded on the second device. On the other hand, in a single system, the audio is captured silmutaneously with the image on the same device. The double recording system is used more so if you do not have a camera that has an advanced audio quality input. If you have a dedicated audio device that can capture audio on an independent device, then you will be guaranteed to get a robust sound quality.