What is oversampling?
It involves sampling the signal at a rate higher than the base sample rate. Oversampling can be analog, when sampling the original signal at an increased frequency, or digital, when additional samples calculated by interpolation are inserted between existing digital samples. Another way to get intermediate sample values is to insert zeros, after which the entire sequence is digitally filtered. The ADC uses analog oversampling, the DAC uses digital.
Oversampling is used to simplify ADC and DAC designs. According to the problem conditions, an analog filter with a linear AFC in the operating range and steeply falling out of it should be installed at the input of the ADC and the output of the DAC. The implementation of an analog filter of this type is quite complex; at the same time, when the sampling frequency is increased, the reflections of the spectrum introduced by it are compensated proportionally with respect to the main signal and the analog filter can have a much lower cutoff slope.
Another advantage of oversampling is that the amplitude quantization errors (squash noise) distributed over the entire spectrum of the signal being quantized are spread over a wider bandwidth when sampling, so there is less noise present. on the main audio signal. Each frequency doubling reduces the quantization noise level by 3 dB; Since one bit equals 6 dB of noise, each quadruple of the frequency reduces the converter’s capacity by one.
Oversampling, coupled with an increase in the sample bit depth, interpolation of the samples with greater precision, and their output to a DAC of the appropriate bit depth, allows for some improvement in the reconstruction quality of the audio signal. For this reason, even 16-bit systems often use 18- and 20-bit oversampling DACs.
Oversampling ADCs and DACs can do without sample and hold circuitry by significantly reducing conversion time.
