Upsampling DACS: Take the Pepsi Challenge

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.

Perhaps I need to ask an even more elementary question to clear my confusion: with an upsampled datastream, what "information" is populated into the additional 16,711,680 word states (16 bit to 24 bit) and what information is packed in between the sampling points (44.1 to 96,192,706,768 kHz)? MSB has returned my e-mail and confirmed that the improvements brought about by upsampling (at least as they implement it) are primarily due to the ability to filter more aggressively outside the audio band, as well as the ability to utilize the greater linearity of the 24 bit DACS they use. Haven't heard back yet from Resolution Audio or Wadia yet, but will post their response when they do.

dCS, the British company that made the first upsampler product, readily admits that there is no known reason why upsampling should sound any better than oversampling. The processes are fundamentally the same. Since many well-trained listeners report that upsampled data sounds more natural and realistic than oversampled equivalents, then I think it is reasonable for listeners and manufacturers to be somewhat confused.

Thanks Onhwy61. I'm not ashamed to admit that I'm a little confused about this subject. The two processes appear VERY similar to me and yet there is quite a stir about upsampling DACs.