Upsampling DACS: Take the Pepsi Challenge

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

I'm trying to tell you, I don't know how else to put it. Oversampling still sends the same data to the DAC. Upsampling sends the DAC data that has been sample rate converted to a much higher resolution format, while still in the digital domain. Oversampling means we are still talking about a DAC that converts 16 bit/44.1 PCM code, to analog. An upsampled data stream is sent to a DAC that (depending on what bit rate/sample rate that data is) is converted to analog with a DAC that could be 24/96, 24/192, 24/706, or 24/768........I thought all of this was common knowledge, and can't understand why you are confused. Certainly any manufacturer will be frustrated by these questions, it seems to me.