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In Reply to: RE: Chord up-samples? posted by yage on June 20, 2017 at 17:03:39
Yes, that's correct. The image bands are still present, which is indicated by the fact that the D/A output still exhibits an stair-stepped appearance, except with finer granularity steps after oversampled digital interpolation is applied. Except, that the image bands are now shifted up in frequency by a multiple of the oversampling ratio. The frequency up-shift makes final image band removal via analog filtering much simpler. Also, as I recall, the SinX/X frequency domain masking effect of zero-order-hold (stair-stepped) D/A units inherently suppresses the oversampled interpolation image bands more effectively than before oversampled interpolation.
My DSP explanations for the lay person aside, I mostly jumped in to counter the commonly expressed notion that since digital interpolation changes the data sample values, it necessarily corrupts the pristine quality of the original data. That is an (intuitive) analog signal domain processing notion, which has nothing to do with (often non-intuitive) digital signal domain processing.
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Ken Newton
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