Careful consideration of the underlying planning. The ideal underlying planning should divide different types of circuits in different regions.
As far as possible the use of differential signal. Audio devices with differential inputs can suppress noise. The differential signal is generally not ground. Because the application of differential signal theory is the most important point is the use of differential signal coupling between the benefits, such as the elimination of magnetic flux, such as the ability to resist noise. If the ground wire is added in the middle, the coupling effect will be destroyed.
Differential pairs of wiring must pay attention to two points, first, the length of the two lines to be as long as possible, and the other is the distance between the two lines (distance from the differential impedance) to remain unchanged, that is, to keep the parallel. There are two parallel ways, one for the two lines to walk in the same line layer (side-by-side), one for the two lines in the upper and lower adjacent to the two layer (over-under). Generally before the side-by-side to achieve more.
Isolate the ground current to avoid the digital current increase the analog circuit noise. Basically, it is true that the module / number partition is isolated. It is important to note that the signal line as far as possible not to cross the division of the place, as well as do not let the power supply and signal return current path changes too large. The analog signal line cannot cross is required because the digital signal slightly faster the return current path will try to go along the line near the lower part of the source of flowing into the digital signal, if the analog signal line cross, noise generated by the return current will appear in analog circuit area.
Analog circuits using star ground. The current consumption of an audio power amplifier is generally large, which may have an adverse effect on their own ground or other reference ground.
Turn unused areas on the circuit board to ground. The ground coverage is achieved near the signal line, so that the excess high frequency energy in the signal line can be divided into the earth through the capacitive coupling.