According to the Nyquist criteria, output samples must be generated at a rate at least twice that of the highest frequency component in the signal the customer wants to re-create. Usually, though, users want to output samples at a much higher rate, at least 8x the highest frequency, because this allows the filter to be a less complex, less expensive design. Now assuming the customer wants to re-create a 1Hz signal. This means that the sampling frequency of the D/A must be at least 2Hz. If they use a simple RC filter at the output, the remnants of the sampling frequency are only 6dB below the signal they are trying to recover (if 1Hz is the 3dB down point). Thus, there would be a lot of ripple. Eliminating that ripple would require a filter with a sharp roll-off. If the sampling frequency is raised to 8Hz, which is three octaves beyond the 1Hz signal, the simple RC filter would now attenuate the sampling frequency to 18dB below the 1Hz signal, so there would be much less ripple. Again, users could readily get a steeper roll-off (and thus a cleaner output waveform) with an active filter. If a sample is taken at a much higher frequency, as can be done with the PWM14 D/A, the digital output consists of huge quantities of short pulses, which greatly relax the filtering criteria. This is because it is generally much easier to filter out high frequencies than low ones.