Upsampling DACS: Take the Pepsi Challenge

Craig, yes dither (white noise) is added to increase resolution. Not sure exactly how that works, but I believe it elevates the recorded data up from the near the least significant bit, reducing quantization errors. Interpolation is basically what is done whenever you increase the sampling rate by some multiple. I don't think that early "oversampling" designs were adding dither before decoding? But if this is the only difference, then my last statement above is probably right: mfg's found better ways to implement oversampling techniques and are marketing them as the "upsampling" process? Either way, it sounds like most listeners have found well done upsampling/oversampling to be a significant improvement.

With upsampling, the digital audio is actually re-sampled, and has nothing to do with the filters in the DAC. The data is sample rate converted to a HIGHER resolution digital format (while in the digital domain), before it even gets to the DAC. The first units of this type used two separate chassis. One was a "sample rate converter", or "digital-to-digital" converter. The data was then sent to a DAC in another chassis. Lately, all-in-one-box units of all types are popping up.

Anyone interested read latest Hi-Fi News & Record Review (August) they have good article on this subject. Wadia apparantly is saying upsampling is no better than their oversampling techniques. Magazine compares latest Wadia 860 against DCS Delius 24/192 upsample unit. Gives good overview of both methods of data processing, too complex to explain here, please read article. To summarize they say Wadia has perfected the CD sound to its highest level, but it still has underlying CD sound characteristics. DCS Delius using upsample somehow takes same data from CD and transforms sound in positive ways to sound more real than traditional oversample. There is no scientific explanation at this time, just subjective opinions of reviewers, regards Sam

It's a shame that Wadia might feel negatively towards upsampling, because their slow roll off filter in their DAC would greatly benefit if it were rolled off way above the audible frequency range, instead of WITHIN the audible range. I had assumed they were moving towards upsampling. Perhaps they'll eventually catch up to the rest...

Megasam, just went out to the local Borders and read the article in "HiFi News and Record Review". Thanks for the notice. Not sure what they were trying to suggest? They only compared the sound of two different units. I would have liked to hear about the differences wrought by sending the Wadia an upsampled data stream via Purcel or Delius (can't keep straight which is the "upsampler"). After reading that article, I'm still left with the same feeling: oversampling and upsampling are VERY similar as far as the processes go. Implementation (how much over/up sampling and amount of dither added) and choice of filter algorithm is likely to be most significant to overall sound. How do you "resample" a digital datastream? You oversample and interpolate the points between original sampling points. You may increase word length also, but this does nothing unless you add dither. I'm not an expert on this, but I do think I'm not far off. I've e-mailed several mfg's with specific questions regarding upsampling/oversampling. Haven't heard back yet, but if it turns out I'm way off base here, I'll report it here and eat my helping of crow. Just want to understand. Greysquirrel