Oversampling

Started by George December 21, 2007
What is the highest oversampling rate in commercial use on high fidelity (15 
kHz) audio nowadays?   I'm not looking for anything leading-edge or very 
pricey.  Just commercially available ADCs that are premium priced but aren't 
extremely expensive.

A few years ago I recall 8X oversampling was considered good without having 
a big cost penalty.   I imagine that rate would be higher today?

Thanks for the help.






George wrote:

> What is the highest oversampling rate in commercial use on high fidelity (15 > kHz) audio nowadays?
Why do you care? It is largely irrelevant to the quality.
> I'm not looking for anything leading-edge or very > pricey. Just commercially available ADCs that are premium priced but aren't > extremely expensive. > A few years ago I recall 8X oversampling was considered good without having > a big cost penalty. > I imagine that rate would be higher today?
???? The typical oversampling ratios in the audio delta sigma DACs/ADCs were 256 or 384. In our days, the oversampling ratios are lower (64 is the most common) due to the use of the multibit delta sigmas. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
George wrote:
> What is the highest oversampling rate in commercial use on high fidelity (15 > kHz) audio nowadays? I'm not looking for anything leading-edge or very > pricey. Just commercially available ADCs that are premium priced but aren't > extremely expensive. > > A few years ago I recall 8X oversampling was considered good without having > a big cost penalty. I imagine that rate would be higher today?
There are commercial 96KHz systems. There are technical reasons that make it desirable to exceed 48KHz for some processing operations, but none for reproduction. Those who claim to hear an improvement when using gold-plated automobile jumper cables to drive their speakers will want this sample rate in their homes. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������

Jerry Avins wrote:

> There are commercial 96KHz systems. There are technical reasons that > make it desirable to exceed 48KHz for some processing operations, but > none for reproduction.
If you look at the output spectrum of an audio DAC, you will see the huge amount of noise at the frequencies above the sample rate. The fairly decent filter is required to get rid of that. The noise is the artifact of the noise shaping. It can possibly affect the quality due to the nonlinear effects, and it causes the EMC problems, too. But what is more important this noise shows up on the A-curve noise measurements, spoiling the otherwise nice figures of SINAD. So there is some sense in using the higher sample rates. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
On Fri, 21 Dec 2007 09:47:03 -0600, Vladimir Vassilevsky
<antispam_bogus@hotmail.com> wrote:

> > >Jerry Avins wrote: > >> There are commercial 96KHz systems. There are technical reasons that >> make it desirable to exceed 48KHz for some processing operations, but >> none for reproduction. > >If you look at the output spectrum of an audio DAC, you will see the >huge amount of noise at the frequencies above the sample rate. The >fairly decent filter is required to get rid of that. The noise is the >artifact of the noise shaping. It can possibly affect the quality due to >the nonlinear effects, and it causes the EMC problems, too. But what is >more important this noise shows up on the A-curve noise measurements, >spoiling the otherwise nice figures of SINAD. So there is some sense in >using the higher sample rates.
That makes pretty good sense, actually. Use a high output sample rate so that you have some unused spectrum to which to move the shaped noise, then remove that with the reconstruction filter. [Guinness guys] BRILLIANT! [/Guinness guys] Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Vladimir Vassilevsky wrote:
> > > Jerry Avins wrote: > >> There are commercial 96KHz systems. There are technical reasons that >> make it desirable to exceed 48KHz for some processing operations, but >> none for reproduction. > > If you look at the output spectrum of an audio DAC, you will see the > huge amount of noise at the frequencies above the sample rate. The > fairly decent filter is required to get rid of that. The noise is the > artifact of the noise shaping. It can possibly affect the quality due to > the nonlinear effects, and it causes the EMC problems, too. But what is > more important this noise shows up on the A-curve noise measurements, > spoiling the otherwise nice figures of SINAD. So there is some sense in > using the higher sample rates.
For reproduction, a good reconstruction filter reduces frequencies above half the sample rate to negligible levels. (If the high signal isn't negligible, the reconstruction filter isn't good.) Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
Eric Jacobsen wrote:
> On Fri, 21 Dec 2007 09:47:03 -0600, Vladimir Vassilevsky > <antispam_bogus@hotmail.com> wrote: > >> >> Jerry Avins wrote: >> >>> There are commercial 96KHz systems. There are technical reasons that >>> make it desirable to exceed 48KHz for some processing operations, but >>> none for reproduction. >> If you look at the output spectrum of an audio DAC, you will see the >> huge amount of noise at the frequencies above the sample rate. The >> fairly decent filter is required to get rid of that. The noise is the >> artifact of the noise shaping. It can possibly affect the quality due to >> the nonlinear effects, and it causes the EMC problems, too. But what is >> more important this noise shows up on the A-curve noise measurements, >> spoiling the otherwise nice figures of SINAD. So there is some sense in >> using the higher sample rates. > > That makes pretty good sense, actually. Use a high output sample > rate so that you have some unused spectrum to which to move the shaped > noise, then remove that with the reconstruction filter.
I don't get it. The noise before filtering always goes above the sample rate, and the reconstruction filter is designed to remove it. A higher-than-needed sample rate allows some noise to be lower than the sample rate, but it needs to be removed anyway. What's the advantage for playback? Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On Dec 21, 8:31 am, Jerry Avins <j...@ieee.org> wrote:
> For reproduction, a good reconstruction filter reduces frequencies above > half the sample rate to negligible levels.
A good reconstruction filter can do that without also effecting a nearby audio passband. A cheap reconstruction filter will require a much bigger transition region, e.g. a sampling frequency much higher than 2X the desired passband. These days, a million more transistors on a die running at a higher frequency might look cheaper to some designers than just a few more high quality discrete components with their associated assembly costs. IMHO. YMMV. -- rhn A.T nicholson d.0.t C-o-M

Jerry Avins wrote:

> Vladimir Vassilevsky wrote: >> Jerry Avins wrote: >> >>> There are commercial 96KHz systems. There are technical reasons that >>> make it desirable to exceed 48KHz for some processing operations, but >>> none for reproduction. >> >> If you look at the output spectrum of an audio DAC, you will see the >> huge amount of noise at the frequencies above the sample rate. The >> fairly decent filter is required to get rid of that. The noise is the >> artifact of the noise shaping. It can possibly affect the quality due >> to the nonlinear effects, and it causes the EMC problems, too. But >> what is more important this noise shows up on the A-curve noise >> measurements, spoiling the otherwise nice figures of SINAD. So there >> is some sense in using the higher sample rates. > > > For reproduction, a good reconstruction filter reduces frequencies above > half the sample rate to negligible levels.
The aliasing is not an issue here. It is taken care off by the digital filtering. The issue is the shaped noise at the output of the oversampling DAC.
> (If the high signal isn't > negligible, the reconstruction filter isn't good.)
That's what I am talking about. A good analog filter of the 4+ order is requred for 48kHz. At 96kHz, you can get with a simple RC of the 2nd order. Vladimir Vassilevsky DSP and Mixed Signal Design Consultant http://www.abvolt.com
Ron N. wrote:
> On Dec 21, 8:31 am, Jerry Avins <j...@ieee.org> wrote: >> For reproduction, a good reconstruction filter reduces frequencies above >> half the sample rate to negligible levels. > > A good reconstruction filter can do that without also > effecting a nearby audio passband. A cheap reconstruction > filter will require a much bigger transition region, e.g. a > sampling frequency much higher than 2X the desired passband. > These days, a million more transistors on a die running at > a higher frequency might look cheaper to some designers than > just a few more high quality discrete components with their > associated assembly costs.
OK. I didn't think we were discussing cost tradeoffs. If we're going to, we need to account for the cost of storing (or transmitting) the extra bits. I have many CDs, but few players. If upsampling before converting to analog saves pennies, I'm all for that. Fitting half as many hours of musiv on the same amount of medium isn't a good trade. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;