Upsampling DACS: Take the Pepsi Challenge

Greysquirrel; I'm no expert here, and I've had some of the same questions that you do. From reading, I've learned that upsampling and over-sampling are not the same thing. Upsampling adds dither, ie it interpolates between digital bits and then adds "sound" based on an upsampling algorithm via a DSP chip. This serves to make the digital data stream more continuous, ie more analog like. Analog meaning a continuous sound stream as opposed to the bit stream of digital output. Over sampling does not add dither or do any interpolating. Maybe Carl can help us out from here. Cheers. Craig.

.... I should have added that over sampling is just used to increase the accuracy of reading standard 16 bit 44.1 HZ CDs, but it adds nothing to the digital output stream. Craig.

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