It’s simplistic to think of a multimedia codec (coder/decoder) as a simple pairing of analog-to-digital and digital-to-analog converters (ADCs and DACs), often with a few “bells and whistles” placed around those functions. After all, the core function of the codec is very basic: Encode analog audio as a digital stream and implement the complementary function of decoding digital audio back into analog, and do so using one or more industry-standard formats.
There’s a strong set of opposing forces at work in codec selection. On one side, designers would like to have a low-power, extremely small device for many reasons. These attributes are especially important since many of the applications are highly portable, such as smartphones, tablets, mobile gaming systems, music players, wireless voice headsets, earbuds, and other audio-enabled and -centric devices. Their codecs need to be extremely efficient in their static, active, and quiescent power consumption, as well as in their dynamic dissipation as audio volume and use-circumstances change.
However, there’s the usual power/performance challenge and dilemma. End-users expect to be able to crank up the volume for noisy surroundings (or maybe they just like it loud), while experiencing no audible hiss at the other end of the volume setting when in quiet surroundings.
There’s also a need to provide mixed-signal functionality for
- Analog and digital volume control
- Low-pass filters that can attenuate higher-frequency noise
- DC-block filters to remove range-diminishing offset from the audio signal
- Dynamic range control that smooths out high-volume peaks
- Filters and equalizers that make it possible to match the audio-output spectrum to the speaker elements in the headphones