low pass filter in PC soundcard?

Rob · 2015-09-10T12:46:59+00:00

When looking at the output of a cheap C-Media CMI8768 based soundcard (one of those tiny PCI-X cards that hold barely more than the chip, a couple of output series caps and the connectors) I noticed there is no low-pass filtering of the DAC output. The output when sending a sinewave is a staircase. The samplerate was set to 48000, 96000 also tried with similar effect. Of course, when the signal is low-pass filtered the result again is a good sinewave. But a random other cheap soundcard shows a nice sinewave directly on the output. Does anyone have expierence with the common practice w.r.t. output filtering in soundcards? Can one expect a low-pass at half the sample rate to be present on a typical low cost soundcard? Is is present in some of the widely used chips and not in others?