Which ADC type is known for high resolution with oversampling and noise shaping, especially at low frequencies (audio applications)?

• A. Flash
• B. SAR
• C. Sigma-delta
• D. Integrating

Answer: (C)

Oversampling with noise shaping is the hallmark of sigma-delta converters. In audio, signals occupy a relatively narrow, low-frequency band, so sampling at a rate much higher than the bandwidth allows most of the quantization noise to be pushed out of the audible range. The sigma-delta modulator converts the input into a high-rate, low-resolution stream while using feedback to shape the quantization noise, concentrating it at higher frequencies. A digital decimation filter then lowers the sample rate and extracts a high-resolution baseband signal, giving many effective bits without demanding an ultra-clean analog front end. This combination makes it ideal for high resolution at low frequencies typical of audio.

Other types don’t match this capability in the same way. Flash converters are extremely fast but offer limited resolution, since their parallel comparators cap achievable accuracy. SAR converters sit between speed and resolution but don’t leverage oversampling and noise shaping to the same extent, so their effective resolution in the audio band isn’t as high. Integrating (or dual-slope) designs are robust and good for DC or very low-frequency measurements, but their bandwidth and typical architectures don’t deliver the same high-resolution performance for audio signals.