It reduces the noise when switching effects. This is a good invention to get pure sound of only audio signal of your guitar after a pedal chain. It stops the unwanted energies filtered to your jack, especially if one of the power supplies creates a DC offset which is noisy energy of transformers that could also do ground loops because the energy without this tool travels freely. This guy is a barrier of stomp pedals DC energy infiltrated in all the cables. It is as simple as that. It is small, as wide as a pedal but length 30%. It cleans up the sounds. The only bad point you need to buy one more jack. It is very useful if you are looking for professional sound. With this you can be sure that the final output will not have an energy that could damage your recording machine. It is suitable to get the best of just one pedal or especially good if you have professional gear where lot of currents are used, so you are safer out of electric shocks. It is suitable also for acoustic guitars with piezo because in this case the 9 volt battery also adds unwanted noises mixed in the sound signal, so the solution is this technology of galvanic isolation where there is no contact but the info is transfered. Lehle DC Filter is passive so needs no battery. It has one jack input and one output. Built solid as a tank. Weights 120 grams. It is very cheap for the good work it does. You can plug either stereo or mono, so it is suitable for other instruments that uses power supplies. It is magnific complement of the splitters of the same brand but also can be used alone. If you care about the quality of your music, consider this product.
