Do Passive Components Degrade Audio Quality in Your Portable Device?

Abstract: In an audio circuit, passive components define the gain, provide biasing and power-supply rejection, and establish DC-blocking from one stage to the next. Portable audio, for which space, height, and cost are usually at a premium, forces the use of passives with small footprints, low profiles, and low cost.

The audible effect of these devices is worthy of some examination, because poor component choice can significantly degrade the measured performance. Some designers assume that resistors and capacitors have no measurable effect on audio quality, but the nonlinear characteristics of many common passives used in the audio signal path can seriously degrade total harmonic distortion (THD). In some cases, the nonlinear contribution of passives exceeds that of active devices such as amplifiers and DACs, which are assumed by many designers to be the limiting factor in audio performance.