post #31 of 54
11/6/08 at 10:03pm
|Upsampling vs. Oversampling
Oversampling in the context of the D-A process involves multiplying the sampling frequency by a whole number, typically between 4 and 32, or even higher. For example, in ‘8x oversampling’, CD’s base rate of 4.4.1kHz is raised to 352.8kHz by introducing seven new ‘empty’ samples between the original data samples.
These new samples, though, are often not just empty strings of noughts, but based on mathematical models to assist the DAC to work more linearly with the extracted data.
Oversampling, as well as easing the workload of the anti-aliasing filter, which can now operate more gently at a higher frequency, can also reduce distortion created when those analogue signals are first turned from continuous, analogue waveforms into stepped, digital, stair-like curves.
This quantization noise is now spread over a larger band after oversampling, and can even be somewhat shifted out of the audible envelope by the technique of noise-shaping. Sony/Philips’ Direct Stream Digital, as used in SACD, takes this idea to its limit, in order to dump high levels of digital noise up to higher frequencies than are not directly audible.
Upsampling is a solely digital domain process where the data stream is also stretched out by interpolation — guessing the points in between, again mathematically — and is typically used to refer to small, non-integer changes, such as from 44.1 kHz to 48kHz. When the change is larger than this, such as 44.1 kHz to 192kHz, ‘upsampling’ is a more popular term.
'There is apparently no extra information in the upsampled signal that was not present in the initial signal,’ says Mike Story of dCS. ‘With a 44.1 kS/s input, both the input data stream and the upsampled data stream will only contain a spectrum that must be between 0 and 22.05 kHz and is probably only between 0 and 20kHz.'
Sorry to hear of your experience. So far, it has been an aberation and not a norm. I hope you won't be discourage from a first mishap.
Kevin is a respectable person and business man. I bought a Valab DAC and tube buffer from him w/o a hitch and am getting more stuff. Sound quality on this piece is just top notch. He's been extremely busy lately due to the popularity of this piece and thus, the delay with answering emails and such.
My buddy went from Benchmark to PS Audio Link III to Bel Canto DAC3. I just did a comparo with the Valab NOS DAC and it killed his DAC3. I don't think the Benchmark will stand a chance if you're into musicality instead of specs.
Luc, I was thinking to grab the DAC3 a while ago but seems fortunately not. I have my Valab 2009 version from 21 Jan till now with some mod and non stop burn-in with 2 CDP alternatively, sounds amazing and am impressed. I have a NOS JOB DA96, the Valab kills the Job in the very first minute. More mod will come later when Bill, Pat, Phill or anyother have more idea in making it better
The comparison I did with the DAC3 was with the Dec. 08 version of the Valab NOS DAC. So, I think there's more to be expected from the 2009 version due to all the latest and greatest update.
Regarding parts swap and such, I would check with Kevin first if he approves of whatever upgrades being proposed as he should know best what can be improved upon with this piece. Can't wait to get the new version to further enjoy my music.