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Digital Drive: Re: Domain Dementia... by csown Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: Domain Dementia... posted by Todd Krieger on August 27, 2003 at 09:10:29:
Todd, the response is abs(Sin(x)/x). It doesn't go negative, you can't have a negative response. We're talking about amplitude here which is the modulus.What you've been thinking about up till now is the sum of fourier coefficients in the time domain summing up to create the impulse response. That is indeed the function A(sin(n.x)/x), a scaled/stretched sinc function - here it does go negative since we are describing the time-domain signal here. The scaling/stretching depends on the fourier coefficients - you can obviously not sample with infinitely fine samples, so you cannot have a perfect top hat function. This is what gives rise to the ringing in the impulse response, and this I know you know.
With non-OS, you can avoid the digital filter ringing because of the zero order hold. The minimum impulse width is 1/ f s , a top hat function (!) made possible by virtue of the ZOH. Just think: real-world impulse response using 40-year-old technology :). Its accuracy is limited only by the slew rate of the DAC and the DAC's post-electronics which, if designed properly, have excellent real-world impulse response way way beyond the audio band. But you don't get it for free - there is still a sinc rolloff in the Bode plot (amplitude/frequency). That is why non-OS DACs that do not employ corrective analog post-filters are not flat across the band. Some non-OS designs will correct for this, some (like me) go on the assumption that this is not a big deal and that phase error due to correction filters muck up the beautiful effects of non-OS so it's not worth it to do it.
Before I forget - I wanted to ask - have you gotten your trial dAck! yet?
-Chris
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Topic - upsampling article - solidgore 08:08:38 08/22/03 ( 47)
- Re: upsampling article - Werner 05:31:36 08/27/03 ( 0)
Erroneous Stuff... - Todd Krieger 14:23:36 08/22/03 ( 44)
- Re: Erroneous Stuff... - csown 21:44:29 08/22/03 ( 43)
- Re: Erroneous Stuff... - Todd Krieger 23:39:51 08/22/03 ( 42)
- Re: Erroneous Stuff... - csown 10:56:04 08/23/03 ( 40)
- Re: Erroneous Stuff... - Todd Krieger 21:24:51 08/23/03 ( 39)
- Re: Erroneous Stuff... - csown 23:37:53 08/23/03 ( 38)
- Re: Erroneous Stuff... - Todd Krieger 15:37:44 08/24/03 ( 34)
- Re: Erroneous Stuff... - csown 16:17:17 08/25/03 ( 33)
- This Wasn't as Bad as Expected... - Todd Krieger 21:31:58 08/25/03 ( 31)
- Re: This Wasn't as Bad as Expected... - csown 21:03:54 08/26/03 ( 26)
- A DAC's "Brickwall Filter" is *Not* the Analog Post Filter... - Todd Krieger 01:04:25 08/27/03 ( 14)
- PMD-100 was one with selectable dither - Wavy Davy 07:29:59 08/27/03 ( 8)
- Re: PMD-100 was one with selectable dither - Todd Krieger 09:18:47 08/27/03 ( 7)
- You can lead a horse to water ..... - Wavy Davy 19:54:26 08/27/03 ( 6)
- But Can't Make Him Drink.... - Todd Krieger 22:10:25 08/27/03 ( 5)
- Re: But Can't Make Him Drink.... - Werner 22:19:27 08/27/03 ( 4)
- High Resolution Signal versus Upsampled Signal - Todd Krieger 22:52:10 08/27/03 ( 3)
- Re: High Resolution Signal versus Upsampled Signal - Werner 23:02:15 08/27/03 ( 2)
- Think About It... - Todd Krieger 00:57:23 08/28/03 ( 1)
- Re: Think About It... - Werner 01:38:26 08/28/03 ( 0)
- Re: A DAC's "Brickwall Filter" is *Not* the Analog Post Filter... - Werner 03:58:47 08/27/03 ( 4)
- Domain Dementia... - Todd Krieger 09:10:29 08/27/03 ( 3)
- Re: Domain Dementia... - csown 08/27/03 10:36:24 08/27/03 ( 2)
- Re: Domain Dementia... - Todd Krieger 12:37:14 08/27/03 ( 1)
- sigh ... - Werner 22:43:03 08/27/03 ( 0)
- Re: This Wasn't as Bad as Expected... - Werner 22:27:06 08/26/03 ( 10)
- Defining upsampling. - csown 08:33:56 08/27/03 ( 9)
- Re: Defining upsampling. - Werner 22:52:31 08/27/03 ( 0)
- Re: Defining upsampling. - Ted Smith 16:07:46 08/27/03 ( 7)
- Re: Defining upsampling. - rfbrw 06:59:09 08/28/03 ( 6)
- Re: Defining upsampling. - Werner 08:20:46 08/28/03 ( 5)
- Re: Defining upsampling. - rfbrw 19:44:47 08/28/03 ( 3)
- Re: Defining upsampling. - Werner 22:36:48 08/28/03 ( 2)
- Re: Defining upsampling. - rfbrw 15:04:47 08/29/03 ( 1)
- Re: Defining upsampling. - Werner 22:34:07 09/2/03 ( 0)
- Re: Defining upsampling. - Todd Krieger 11:31:43 08/28/03 ( 0)
- Re: This Wasn't as Bad as Expected... - Werner 23:34:54 08/25/03 ( 3)
- ZOH... - csown 16:50:11 08/26/03 ( 2)
- Re: ZOH... - Werner 22:32:08 08/26/03 ( 1)
- Re: ZOH... - csown 07:43:04 08/27/03 ( 0)
- I'm Not Ignoring You... - Todd Krieger 18:33:48 08/25/03 ( 0)
Upsampling sample provided by philips 963sa - gialitt 02:25:34 08/24/03 ( 2)
- Re: Upsampling sample provided by philips 963sa - Todd Krieger 21:59:55 08/25/03 ( 1)
- Re: Upsampling Products - gialitt 08:53:05 08/26/03 ( 0)
Followed by confused stuff (nt) - rfbrw 07:22:40 08/23/03 ( 0)
Good article in general... - csown 13:23:21 08/22/03 ( 0)