5、Why can interference noise be heard when downloading or playing through WiFi?

A. The X7 is prone to some low level of WiFi-induced noise in the headphone output by nature.

As you know, the X7 prides itself on having discrete SoC, DAC, voltage amplification and current buffer sections (the latter two being placed in the interchangeable amplifier module). We still believe that such an approach offers the highest audio fidelity possible. However, such an approach also carries with it great sensitivity to radio noise, as analog audio circuits are spread out all over the X7 internals, ready to pick up radio interference from any source. Great pains must be taken to minimize the effect of any such interference and even then some effect on the audio output cannot be avoided when WiFi is on and transmitting.

There are countless smartphones on the market that can play music without apparent interference while streaming music through WiFi, or e.g. surfing Facebook, for that matter. There are several features that can make such radio noise rejection performance possible:
1. High level of integration of the analog audio circuits (preferably totally integrated within the SoC itself) for minimum analog circuit footprint.
2. Class D amplification, in effect turning the amplifier circuit into a digital circuit, immune from RFI. The analog audio signal is recovered only at the end of the circuit through a low pass filter.
3. Low power output, in particular a low maximum gain. This simply attenuates the RFI via the reduced gain level.

As you can see, each of these radio-friendly design features has great potential to degrade audio quality. Coming from a background of offline audio players, FiiO did not realize the great extent to which the perception of audio quality of an online-capable player would be driven by the compromise quality while streaming online audio. The natural approach was to design the player as a music player first and online device second. Hence, while we believe the X7 offers nearly unparalleled offline music performance at its price, the noise level while online may leave something to be desired.

If using sensitive IEMs, (e.g. BA IEMs / CIEMs of under 20ohms impedance), some level of interference noise can be expected to be heard from any X7 unit, in a quiet environment, with quiet music, while the WiFi is transmitting / receiving.

However, such noise is usually drowned out by the music itself, and stops once the music has been buffered. It cannot be heard on less sensitive earphones or headphones.

If you're using sensitive IEMs / CIEMs, we suggest that you listen more to offline music and / or buffer/download online music in advance, to take advantage of the X7's uncompromising offline audio performance. 

B. However, there is also a QC problem with some X7's suffering from excessive noise.

As McCol first demonstrated, some X7's suffer from excessive interference noise that are the result of a manufacturing problem rather than design problem. The symptoms of such excessive interference are:
1. Obvious interference noise that can be heard with any headphone, including full-size over-ear headphones.
2. X7 has great tendency to indicate a weak WiFi signal even when close to the WiFi hotspot.

Such excessive interference are the result of a fault in wiring the WiFi antenna and the shielding within the X7. The faulty WiFi antenna makes unusually high levels of radio emissions as it attempts to acquire the signal, while the faulty shielding allows such radio emissions to interfere with the audio signal to a great extent.

C. The criterion for returning the X7 for a WiFi fault is?

As outlined by A and B, some low level of WiFi generated radio interference is normal while a high level of interference is indicative of a faulty unit. However, there is also great variability in the level of interference that may be experienced with a faulty unit, since

1. the manufacturing fault can affect the resulting interference to variable extents
2. different WiFi hotspots communicating with the X7 can cause different levels of interference, and
3. different headphones and different listeners will pick up the resulting interference to differing extents.

Since none of these factors are under control by the customer evaluating his X7, there has to be criteria for declaring an X7 faulty that can be readily evaluated by the customer. We have settled on the criterion that if the interference noise can be heard through any one or more pairs of on-ear or over-ear headphones you own--as opposed to earbuds or IEMs,

we will readily accept its return / exchange (in the return / exchange period) or take it in for repair (in the warranty period).

On the other hand, we will not be carrying out any cross-examination of the customer's claims on the above when evaluating returns. We are depending on your goodwill as a FiiO customer to return genuinely problematic units to us and see us through this difficult period for our company.