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Digital Drive: Re: Domain Dementia... by Todd Krieger Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: Re: Domain Dementia... posted by csown on August 27, 2003 at 10:36:24:
"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."I guess so. Although I'd cringe at the the notion of how a DAC that had a frequency response curve like that would *sound* like... [-;
"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."
I see what you're saying. The sum of the FIR coefficients convolved with a pulse signal in real time. Which indeed would yield the impulse response. (I've never heard these called "Fourier coefficients.") This response shows the function of the filter.
"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."
This is the *only* way in digital audio the "sinc" function is applied. It goes negative simply because an audio signal can go negative.
"But you don't get it for free - there is still a sinc rolloff in the Bode plot (amplitude/frequency)."
There is a rolloff, but a non-OS or ZOH DAC does not use a "sinc" filter, since it would require a digital (oversampling/upsampling) filter to implement it. The rolloff is caused by modulation in the HF (the samples do not always occur at the peaks of HF signals), causing the *average* amplitude to decrease, hence the measured rolloff. (The *peak* amplitude would be about the same.)
"That is why non-OS DACs that do not employ corrective analog post-filters are not flat across the band."
The post filter is needed *more* with non-OS because no prior (digital) filtering has been applied. Otherwise, the ultrasonic images of the signal would pass through the output at *full* intensity if no such filter was used. (Some have claimed that zero filtering causes havoc with downstream electronics due the excessive HF content.)
"Before I forget - I wanted to ask - have you gotten your trial dAck! yet?"
Still waiting for it. Thanks.
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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 10:36:24 08/27/03 ( 2)
- Re: Domain Dementia... - Todd Krieger 08/27/03 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)