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In Reply to: RE: REVIEW: MHZS CD 66E CD Player/Recorder posted by Todd Krieger on June 09, 2007 at 12:27:10
Hi Todd - Judging from many of your posts I've read before, your understanding of upsampling vs oversampling vs non-oversampling is much deeper than my own. Form the Pacific Valve website, there is a link that attempts to explain these differences.http://victrolax.blogspot.com/2006/06/whats-with-oversampling-upsampling-and.html
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. 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.
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:
OVERSAMPLING:
"In a 4X oversampler, the digital signal is fed through a special digital converter that samples it four times. When a CD is sampled four times the sample rate becomes 176.4 kHz(44.1 X 4). When the filter is applied here, there is less of chance that the filtering roll off will make its way into the audible range. A filter applied at 176.4 kHz sweetens the music as it removes most of the grunge. As cost allows, oversampling pays off in a big way. The DAC 60 and DAC 38 use Burr Brown’s latest PCM1704UK chip which is 8X oversampling at 96kHz. The DAC 68 uses Analogue Devices AD1835 chip which samples as high as 192kHz. The AD1853 is fully compatible with all known DVD formats and supports 48 kHz, 96 kHz and 192 kHz sample rates with up to 24 bits word lengths. The higher bit lengths of these DACs allow them to act more in a linear fashion during the conversion process and results in superior sound quality."UPSAMPLING:
"So what is “upsampling”? First let me take away some of the confusion. There is belief in many an audiophiles’ minds about the power of upsampling or oversampling to create data. It is not possible to create more accurate information than is already in the digitally sampled signal. Think of blowing up a digital picture: if the data is not there, blowing it up does not increase detail.Upsampling differs from oversampling in that upsampling is between the transport and the DAC. In the case of the Lite DAC 39, it sits between your transport (CD player) and a DAC – like the DAC 60 or DAC 38. In this case the DAC 39 feeds the DAC 60 a 96 Khz signal instead of the 44.1 kHz. In theory, when a superior upsampler is mated with a DAC that can handle the upsampling, the true 96kHz 20 bit processing can be achieved. The resulting filtering process operates in a linear fashion which yields better sound quality. So, it has to be a careful match. An upsampler should only be used with a DAC capable of handling the high sample frequency. "
Ken
Edits: 06/09/07 06/09/07Follow Ups:
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