Upsampling vs zero oversampling

studley · « **on:** 8 Nov 2005, 09:40 pm »

Steve
your website suggests that the off ramp turbo produces the best results when used with 24/96 upsampling. In contrast zero oversampling now has some noteworthy advocates including Mr 47 Labs. Given that one of the USB - DAC alternatives, the Brick, uses zero oversampling I was wondering what your thoughts are on this up vs zero debate.

audioengr · « **Reply #1 on:** 9 Nov 2005, 06:22 pm »

Quote from: studley

Steve
your website suggests that the off ramp turbo produces the best results when used with 24/96 upsampling. In contrast zero oversampling now has some noteworthy advocates including Mr 47 Labs. Given that one of the USB - DAC alternatives, the Brick, uses zero oversampling I was wondering what your thoughts are on this up vs zero debate.

I still like upsampling to 24/96 using Foobar and SRC on the computer. Also, the Perpetual Tech P-1A upsampler is very good now that I have a definitive mod for it. Other hardware upsamplers that I have heard are not so good. the Off-Ramp sounds better than other stock converters whether you upsample or not. iTunes with no upsampling on a MAC is very fine indeed.

The nice thing about computer audio is that you can choose not to upsample if you like, assuming that your DAC does not automatically do it. The USB DAC that I am currently designing will not have upsampling enabled unless you want it.

Steve N.

studley · « **Reply #2 on:** 9 Nov 2005, 08:36 pm »

I have recently acquired a G4 ibook to use as a music server and once I've got fully set up (at present I'm inclined to wait for your 12s off ramp converter but is the USB DAC you mention a different future product? ) I will need to to check out the 24/96 Mac option you refer to on your website.

However, my original question was not about upsampling vs normal oversampling but upsampling vs zero oversampling/upsampling.[/b]

ctviggen · « **Reply #3 on:** 9 Nov 2005, 08:54 pm »

I think Steve answered your question. Zero oversampling is like the Ack Dack -- ie, non oversampling. What's "up sampling"? "over sampling" is when you add samples between samples of the digital signal. What's "up sampling"?

studley · « **Reply #4 on:** 9 Nov 2005, 09:05 pm »

Bob
As I understand it, upsampling is the term used to describe the extrapolation of further samples to produce a 24/96 or even a 24/192 digital signal. Oversampling is just the usual 16/44.1 that traditional DACs do. But that's only a layman's understanding and it may well be wrong!
Ian

viggen · « **Reply #5 on:** 9 Nov 2005, 09:18 pm »

I concur with Ian. Up and Over are different. One converts the original into hi-rez. The other corrects mathematical errors in the dac process. Also, I think there's no such thing as pure non-os as a dac inherently has 1x oversampling.. that's why audio note dacs with "non-os" are denoted with a ".1x".

ctviggen · « **Reply #6 on:** 9 Nov 2005, 10:09 pm »

You are correct! I got my own terminology wrong! (A good cite: Oppenheim and Schafer, Discrete-Time Signal Processing, pp. 101-111; this used to be considered the "bible" of discrete-time processing.) So, "oversampling" is sampling at at least the Nyquist rate, which is twice the frequency of the highest frequency component. In audio, the highest frequency component is assumed to be 20kHz, so the Nyquist rate is 40kHz. Upsampling would then take the 40kHz samples and interpolate between them to make higher frequencies. In terms of "real" audio, they use 44.1kHz instead of 40kHz sampling rate. The 96 kHz is about twice this rate, so there would be twice the number of "required" samples (note to self -- why isn't this exactly twice the 44.1kHz?).

Then, what would zero upsampling or zero oversampling be?

audioengr · « **Reply #7 on:** 10 Nov 2005, 07:58 pm »

I believe oversampling may be just clocking at higher frequencies but not adding any new data to the samples, just repeating the same samples, whereas upsampling means interpolation, adding new different samples. I could be wrong...

Most DAC's either do no upsampling or some type of upsampling.

PhilNYC · « **Reply #8 on:** 10 Nov 2005, 08:38 pm »

Here's a 1-pager that describes my understanding of upsampling vs. oversampling...

http://www.resolutionaudio.com/Up-Oversampling.pdf

skrivis · « **Reply #9 on:** 17 Mar 2006, 09:28 pm »

Quote from: ctviggen

You are correct! I got my own terminology wrong! (A good cite: Oppenheim and Schafer, Discrete-Time Signal Processing, pp. 101-111; this used to be considered the "bible" of discrete-time processing.) So, "oversampling" is sampling at at least the Nyquist rate, which is twice the frequency of the highest frequency component. In audio, the highest frequency component is assumed to be 20kHz, so the Nyquist rate is 40kHz. Upsampling would then take the 40kHz samples and interpolate between them to make h ...

The 96 is likely because it's double 48, and 48 is what professonial digital recorders use. (DAT was 48 KHz, for instance.) They didn't usually drop down to the 44.1 used for CDs until later on in the recording/production process.