Forums

Oversampling

Started by George December 21, 2007
Vladimir Vassilevsky wrote:
> > > 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.
by^ Sure. So if it's cheaper, interpolate to even 192 KHz before converting back to analog. *Storing* the information at half (or quarter) density is wasteful. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
"Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message 
news:ehQaj.499$El5.240@newssvr22.news.prodigy.net...
> > > George wrote: > >> What is the highest oversampling rate in commercial use on high fidelity >> (15 kHz) audio nowadays? > > Why do you care? It is largely irrelevant to the quality. >
Understood. My question was not related to quality. I'm asking in connection with an application that is totally unrelated to that. I'll be running 15 kHz audio into an ADC simply for the purpose of generating a digital output. I'd like to achieve a high sampling rate output and am trying to get a handle on what that rate could be. There will be no filtering or conversion back to analog.
George wrote:
> "Vladimir Vassilevsky" <antispam_bogus@hotmail.com> wrote in message > news:ehQaj.499$El5.240@newssvr22.news.prodigy.net... >> >> 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. >> > > Understood. My question was not related to quality. I'm asking in > connection with an application that is totally unrelated to that. > > I'll be running 15 kHz audio into an ADC simply for the purpose of > generating a digital output. I'd like to achieve a high sampling rate > output and am trying to get a handle on what that rate could be. There will > be no filtering or conversion back to analog.
George, This appears to be a one-off application, so $.35 or $5.35 probably isn't a strong consideration. You could run at a couple of MHz if you want to. Where will you store the data? 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;
"Jerry Avins" <jya@ieee.org> wrote in message 
news:Eamdnb0ukrr5vPHanZ2dnUVZ_h3inZ2d@rcn.net...

<snip>


> George, > > This appears to be a one-off application, so $.35 or $5.35 probably isn't > a strong consideration. You could run at a couple of MHz if you want to. > Where will you store the data? > > Jerry
Hi Jerry, You're right - cost isn't a strong consideration. Let me see if I understand what you mean by "a couple of MHz". With 16-bit encoding at 8X, that would be 352.8 kHz sample rate and 5.644 Mbps bit rate. You were referring to the sample rate? A couple of MHz sample rate is about five times faster than the above, which comes to 40X if I understand you correctly. That's what I was trying to get to. Regarding data storage, there isn't any. The stream out of the ADC is being analyzed on the fly to look for patterns, then thrown away. Thanks George
On Fri, 21 Dec 2007 11:37:01 -0500, Jerry Avins <jya@ieee.org> wrote:

>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
How do you move the shaped noise above the sample rate without it also being within the Nyquist region? As has been discussed, the higher the output sample rate the more room there is spectrally for the shaped noise and filter transition band. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
George wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message > news:Eamdnb0ukrr5vPHanZ2dnUVZ_h3inZ2d@rcn.net... > > <snip> > > >> George, >> >> This appears to be a one-off application, so $.35 or $5.35 probably isn't >> a strong consideration. You could run at a couple of MHz if you want to. >> Where will you store the data? >> >> Jerry > > > Hi Jerry, > > You're right - cost isn't a strong consideration. > > Let me see if I understand what you mean by "a couple of MHz". With 16-bit > encoding at 8X, that would be 352.8 kHz sample rate and 5.644 Mbps bit rate. > You were referring to the sample rate? > > A couple of MHz sample rate is about five times faster than the above, which > comes to 40X if I understand you correctly. That's what I was trying to get > to. > > Regarding data storage, there isn't any. The stream out of the ADC is being > analyzed on the fly to look for patterns, then thrown away.
The faster you go, the more data there is to sift through for patterns. The oversampling doesn't add more usable data -- the signal is completely described by the practical rate -- it just adds more samples to look at and discard. Is an integer ratio of actual to minimum sample rate a requirement? Why, for example, 8x. Why not 9.16x? 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 11:37:01 -0500, Jerry Avins <jya@ieee.org> wrote: > >> 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 > > How do you move the shaped noise above the sample rate without it also > being within the Nyquist region? > > As has been discussed, the higher the output sample rate the more room > there is spectrally for the shaped noise and filter transition band.
I understand why getting more bits worth of significance needs faster sampling -- there's more than one way to make that trade -- but once the low-noise signal is acquired, why keep the superfluous samples? 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;
"Jerry Avins" <jya@ieee.org> wrote in message 
news:qq-dnTTzvceWsPHanZ2dnUVZ_vamnZ2d@rcn.net...

<snip>

> The faster you go, the more data there is to sift through for patterns. > The oversampling doesn't add more usable data -- the signal is completely > described by the practical rate -- it just adds more samples to look at > and discard. Is an integer ratio of actual to minimum sample rate a > requirement? Why, for example, 8x. Why not 9.16x?
True about not adding more usable data. But in this application what we're looking for is accurate measurement of the time when the analog waveform satisfies a certain condition. The more frequently we sample it, the more accurately we can time-tag the input condition when it occurs. We'd like to obtain an accuracy of better than the sampling interval at 352.8 ksamples/sec. (Hope I'm not missing something here.) How much of a processing load is created at this speed still has to be determined however. The integer ratio isn't important - was just using it to be brief.
George wrote:
> "Jerry Avins" <jya@ieee.org> wrote in message > news:qq-dnTTzvceWsPHanZ2dnUVZ_vamnZ2d@rcn.net... > > <snip> > >> The faster you go, the more data there is to sift through for patterns. >> The oversampling doesn't add more usable data -- the signal is completely >> described by the practical rate -- it just adds more samples to look at >> and discard. Is an integer ratio of actual to minimum sample rate a >> requirement? Why, for example, 8x. Why not 9.16x? > > True about not adding more usable data. But in this application what we're > looking for is accurate measurement of the time when the analog waveform > satisfies a certain condition. The more frequently we sample it, the more > accurately we can time-tag the input condition when it occurs. We'd like to > obtain an accuracy of better than the sampling interval at 352.8 > ksamples/sec. (Hope I'm not missing something here.)
That's a processing trade-off then. The extra samples you get will contain no more accurate information than you would get from interpolating at the lower rate, *provided the higher sample rate really is oversampling*. At the higher rate, you can include higher frequencies in the samples stream and thereby achieve better time discrimination than you could through the anti-alias filter suitable for the lower rate. That is sampling faster, but not oversampling as I understand the term.
> How much of a processing load is created at this speed still has to be > determined however. The integer ratio isn't important - was just using it > to be brief.
Good luck. 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;
Thanks Jerry ... :o)


"Jerry Avins" <jya@ieee.org> wrote in message 
news:NMidnZUBbo3Qp_HanZ2dnUVZ_uevnZ2d@rcn.net...
> George wrote: >> "Jerry Avins" <jya@ieee.org> wrote in message >> news:qq-dnTTzvceWsPHanZ2dnUVZ_vamnZ2d@rcn.net... >> >> <snip> >> >>> The faster you go, the more data there is to sift through for patterns. >>> The oversampling doesn't add more usable data -- the signal is >>> completely described by the practical rate -- it just adds more samples >>> to look at and discard. Is an integer ratio of actual to minimum sample >>> rate a requirement? Why, for example, 8x. Why not 9.16x? >> >> True about not adding more usable data. But in this application what >> we're looking for is accurate measurement of the time when the analog >> waveform satisfies a certain condition. The more frequently we sample >> it, the more accurately we can time-tag the input condition when it >> occurs. We'd like to obtain an accuracy of better than the sampling >> interval at 352.8 ksamples/sec. (Hope I'm not missing something here.) > > That's a processing trade-off then. The extra samples you get will contain > no more accurate information than you would get from interpolating at the > lower rate, *provided the higher sample rate really is oversampling*. At > the higher rate, you can include higher frequencies in the samples stream > and thereby achieve better time discrimination than you could through the > anti-alias filter suitable for the lower rate. That is sampling faster, > but not oversampling as I understand the term. > >> How much of a processing load is created at this speed still has to be >> determined however. The integer ratio isn't important - was just using >> it to be brief. > > Good luck. > > 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;