I understand current cell phones use digital communications. Given that this industry brings in billions of dollars each year, there is much incentive to get the best performance possible. So what method of reconstructing an audio signal from discrete samples is normally used in a good cell phone these days? It seems there must be methods that work better than the ones I read about in text/reference books.
Answer
Some recent cell phone models use something like a Cirrus Logic CS42xx series audio IO chip, which seems to use a digital polyphase interpolation filter, a sigma delta modulator, followed by a switched capacitor DAC and low-pass filter.
Sinc interpolation (or, given finite hardware, a polyphase FIR kernel similar to a windowed Sinc) is one high quality method of reconstruction from bandlimited samples.
But reconstruction isn't the main issue with respect to audio quality. Quality or fidelity is more likely constrained by the audio data compression algorithm used (or required by standardization), and how much spectrum bandwidth is allocated by the comunications standard and regulations.
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