Upsampling DACS: Take the Pepsi Challenge

Perhaps someone on this thread can clear something up for me? I asked the question before on Audiogon: what are the differences between upsampling and oversampling? Carl, you seem to be one of many fans of the improvement wrought by upsampling. Can you explain the difference or are there differences? My understanding is that upsampling and oversampling are basically the same. By upsampling/oversampling the digital filtering can be more aggressive (outside the audio range), leaving only a gentle analog filter before output. Is this basically correct? Upsampling/Oversampling can't actually create information; the process can only allow more accurate retrieval of what is contained in the 16/44.1 signal. Right? As for oversampling, all delta/sigma (1 bit) type DACS must use oversampling. Are the new 24/96 DACS mostly delta/sigma types or are they ladder DACS? Don't mean to divert attention from the thread topic, but the recent attention to upsampling has me wondering if my understanding of the process is correct. Did mfg's just get better at implementing oversampling techniques to get better sound and needed new marketing jargon to draw interest? Thanks!

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.