Frequency range s of digital noise s

Emitted is the key word here. Emissions are the same as radiated emissions. Most products are limited by Class B to less than 40bDuV/m, at least those that pass Class B testing. This is low enough so you will not have interference between components. Interference of clocks and SMPS supplies inside a component is certainly possible, but usually affecting only jitter in digital systems, not causing errors. Jitter is affected because signal noise levels are increased. Generally in good designs, the problem is more power supply electrical noise, magnetic fields and ground return paths that are more problematic, not emissions.

The thing to understand is that usually the only components that are even sensitive to radiated emissions are tuners, and these can pick up uV of EM radiation.

In typical audio systems, the component-component problem is ground-loops picking up EMI. Eliminate the ground loops and the problem is gone. If the ground-loop is retuned by making it larger diameter or smaller and maybe by twisting the power cords together to minimize the loop area, this can be a fix. Its usually when the ground loop is a size that acts like an antenna that serious problems occur. The area tunes a specific frequency and its harmonics.

Steve N.
Empirical Audio

Ptss - Designers usually don't target specific frequencies and the good ones avoid using too many filters. Filters usually impact SQ. Sometimes designers must add ferrite beads or similar to pass FCC class B emissions.

Good design practices are the best way to avoid emissions and susceptibility. These include good ground-plane design, trace topology and impedance control, proper transmission-line termination and internal cabling impedance/termination. Using the correct connectors does not hurt either.

Filters can be useful and will not impact SQ if used on the ground-wires of cables that are differential or the ground-wires of power cords. Filters on power supplies usually impact SQ, even AC lines.

AC lines can radiate emissions if there is a generator present, such as SMPS that puts HF noise back into the power line. Some wallwarts are notorious for this. By themselves the frequencies on the AC service are too low to have much EMI. Magnetic fields are more prevalent with AC lines.

I am not a fan of conditioners, with one exception, the Plasmatron from VHaudio.com. This really improves SQ for digital. I use one and many of my colleagues use one. The Plasmatron is an AC voltage regulator, not a filter.

Filters on AC generally reduce dynamics, so I steer clear.

Isolation is the best solution, both for digital and analog. I use both, so I have no ground-loops.

Steve N.
Empirical Audio