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RE: Non Oversampling (NOS) DAC's

"1) There is the well known high-frequency roll-off of about 3dB at 20KHz due to the zeroth-order hold operation of R2R ladder DACs. I don't believe that sigma-delta DACs have this problem due to their high inherent oversampling operation, pushing any such roll-off way up in frequency."

The "rolloff" in NOS products is due to modulation taking place toward the upper limit of the working audio range, which is half the sample frequency. Although the average amplitude is indeed down at 20 kHz, the peak amplitude is roughly the same. (The filtering in oversampling DACs "smooths out" the modulation, raising the average amplitude to "flat" up to 20 kHz.) This could be why people don't "hear" the rolloff in NOS DACs. Some might perceive more HF energy, in spite of the measured rolloff. Although some of the HF energy is a result of the modulation.

This modulation is benign when playing simple music, but I think this is what obscures background information and inner detail in complex music.

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