While smart phones have improved in audio quality in recent years, what are the actual differences? Using earphones as an example, Figure 1 shows the results of measuring audio distortion (THD + N).
As shown by this figure, we can see that the audio quality differs by manufacturer.
Common ferrite beads were used for noise suppression in the internal audio circuits of smart phones with poor THD + N results, but the models that emphasized audio quality used the NFZ Series.
The human ear is sensitive, and even slight distortion is heard, particularly in cases such as earphones in which the sound is delivered directly to the ear.
As the shift toward high-resolution audio continues to advance not only in specialized audio equipment, but also in smart phones, audio filters that consider the impact on audio quality will become increasingly important.