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In Reply to: RE: REVIEW: MHZS CD 66E CD Player/Recorder posted by McGruder on June 09, 2007 at 15:31:36
"The term 'upsample' is used to describe my CD player's DAC architecture. I'm not sure if 'oversample' and 'upsample' are correctly defined here, or if they are interchangable terms."
They've been interchanged, and there is no official definition or distinction. The older "synchronous" technology is generally accepted as "oversampling", and newer "asynchronous" technology is accepted as "upsampling."
"This link attempts to describe 4X oversamplers and upsamplers as different categories of DAC's. It leads me to believe that oversamplers create the extra samples within the DAC, and that upsamplers create extra samples between the transport and DAC that supports the higher sampling rates."
Which is usually (but not always) the case. But they both do the digital filtering, so ultrasonic artifacts in the digital signal are minimized.
"This doesn't exactly clear everything up for me, like what is the basis for the values in the extra samples in either case. Is it just interpolation on the 44.1 rate more or less? I'll provide the following excerpts and allow you to comment:"
The interpolation occurs in both cases. The values are numerically calculated via process known as "convolution", where the digital stream from the CD is "convolved" with a fixed finite function. (Usually a "truncated sinc" function.) The intention is to push the first alias much higher in frequency, so minimal analog (post) filtering is needed after the DAC. The function also flattens the frequency response in the audio band, relative to the non-filtered version of the signal.
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