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DAC IV stages
Yahzi
post Feb 20 2013, 18:38
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How important are DAC IV stages in the design of a DAC? I've heard they can cause audible differences. Is this true? I'm not a DAC designer, but I assume there are those who understand the technical merits. Is it a big deal?
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John_Siau
post Feb 20 2013, 22:52
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Take a look at published specifications for D/A converters, DVD players, sound cards, iPod, etc. Many only have an 80 to 90 dB SNR. This means that the noise will be audible in an A/B/X test if the peak music levels exceed 80 to 90 dB SPL (easily achieved).

Worse yet, most D/A converters are preceded by a digital volume control. If 20 dB of digital attenuation is dialed in (very typical), the SNR will degrade by 20 dB. In many systems, the user will need to apply 20 dB of digital attenuation to achieve a playback level that peaks at 100 dB SPL. Under these conditions the converter noise may reach 30 to 40 dB SPL. It is not hard to hear the noise floor drop from 30 of 40 dB SPL to less than 0 dB SPL in an A/B/X test.

I have an ABX tester, and it is very easy to pick out D/A converters that have high noise floors.

If one wishes to use a digital volume control, the D/A converter will need an extra 20 dB SNR to keep noise inaudible at loud playback levels. If we want to achieve "CD" quality and use 20 dB of digital attenuation, then 116 dB SNR is required. Under these conditions, noise may still become audible if playback peaks exceed 96 dB SPL.

D/A converters with >116 dB SNR are few and far between. Noise alone is a dead giveaway when comparing D/A converters.

This post has been edited by John_Siau: Feb 20 2013, 22:57


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Arnold B. Kruege...
post Feb 21 2013, 16:04
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QUOTE (John_Siau @ Feb 20 2013, 16:52) *
D/A converters with >116 dB SNR are few and far between. Noise alone is a dead giveaway when comparing D/A converters.


I guess that TI, Crystal Semiconductor, and AKM have been pulling our chains because they all have fairly inexpensive chips that do 115-120 dB dynamic range. ;-)

I've had a LynxTwo since what, 2002 that met that criteria and they are hardly rare. That isn't specsmanship because I've measured it myself. The same converters or competitive converters are now in the < $5 per channel price range.

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John_Siau
post Feb 21 2013, 16:28
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QUOTE (Arnold B. Krueger @ Feb 21 2013, 10:04) *
QUOTE (John_Siau @ Feb 20 2013, 16:52) *
D/A converters with >116 dB SNR are few and far between. Noise alone is a dead giveaway when comparing D/A converters.


I guess that TI, Crystal Semiconductor, and AKM have been pulling our chains because they all have fairly inexpensive chips that do 115-120 dB dynamic range. ;-)

I've had a LynxTwo since what, 2002 that met that criteria and they are hardly rare. That isn't specsmanship because I've measured it myself. The same converters or competitive converters are now in the < $5 per channel price range.

Most commercial products do not achieve the published specifications provided by the IC manufacturers. These specifications are an indication of the best performance that can be achieved by these parts on an ideal evaluation board, using lab power supplies. Lots of things go wrong when manufacturers cram a bunch of parts in a small package while trying to meet cost and schedule targets. The LynxTwo is a pro product and was not subject to the same design goals as consumer products.

The audio performance of the D/A converters in consumer devices such as TVs, DVD players, portable audio devices, and cable boxes do not come close to 115 dB SNR. Of equal importance is the fact that nobody listens to these devices with the included digital volume control set to 100%. Furthermore, the included digital volume controls are usually not dithered (they truncate).

A meaningful ABX test should attempt to replicate the most demanding typical use:

1) Digital volume control at typical setting
2) Loud but reasonable playback levels
3) Reasonably quiet room
4) Accurately matched levels
5) Low-noise source material

If A and B cannot be distinguised under the above conditions, then it is fair to say that neither offers a sonic advantage over the other in typical use.

This post has been edited by John_Siau: Feb 21 2013, 16:53


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Posts in this topic
- Yahzi   DAC IV stages   Feb 20 2013, 18:38
- - John_Siau   The I-V (current to voltage) conversion stage of a...   Feb 20 2013, 20:48
|- - Soap   QUOTE (John_Siau @ Feb 20 2013, 14:48) Fo...   Feb 21 2013, 03:37
|- - John_Siau   QUOTE (Soap @ Feb 20 2013, 21:37) QUOTE (...   Feb 21 2013, 15:20
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 09:20) QU...   Feb 21 2013, 16:09
- - Yahzi   Thanks for the reply John. I'm getting a few p...   Feb 20 2013, 21:47
- - John_Siau   Designing an I-V converter with a 130 dB SNR is no...   Feb 20 2013, 22:02
|- - Yahzi   But it is largely irrelevant if it is competently ...   Feb 20 2013, 22:28
||- - benski   QUOTE (Yahzi @ Feb 20 2013, 16:28) But it...   Feb 20 2013, 22:44
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:02) De...   Feb 21 2013, 16:11
|- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 16:47
- - John_Siau   Take a look at published specifications for D/A co...   Feb 20 2013, 22:52
|- - saratoga   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 20 2013, 23:51
||- - John_Siau   QUOTE (saratoga @ Feb 20 2013, 17:51) 80d...   Feb 21 2013, 14:57
||- - saratoga   QUOTE (John_Siau @ Feb 21 2013, 08:57) QU...   Feb 21 2013, 20:00
||- - John_Siau   QUOTE (saratoga @ Feb 21 2013, 14:00) All...   Feb 21 2013, 23:03
||- - saratoga   QUOTE (John_Siau @ Feb 21 2013, 17:03) QU...   Feb 21 2013, 23:23
|||- - John_Siau   QUOTE (saratoga @ Feb 21 2013, 17:23) QUO...   Feb 22 2013, 15:15
||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 09:15) QU...   Feb 22 2013, 16:33
|||||- - saratoga   QUOTE (scuttle @ Feb 22 2013, 09:49) From...   Feb 22 2013, 17:58
|||||- - scuttle   QUOTE (saratoga @ Feb 22 2013, 16:58) QUO...   Feb 22 2013, 19:01
|||||- - saratoga   QUOTE (scuttle @ Feb 22 2013, 13:01) No. ...   Feb 22 2013, 19:39
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 13:39) Wel...   Feb 22 2013, 20:13
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:13) Bo...   Feb 22 2013, 20:36
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 14:36) Lik...   Feb 22 2013, 20:46
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:46) QU...   Feb 22 2013, 20:53
||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 14:53) Roc...   Feb 22 2013, 21:13
||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 15:13) QU...   Feb 22 2013, 21:38
|||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 15:38) The...   Feb 22 2013, 22:21
|||||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 16:21) Bu...   Feb 22 2013, 22:24
|||||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 16:24) QUO...   Feb 22 2013, 22:38
|||||||- - greynol   QUOTE (John_Siau @ Feb 22 2013, 13:38) So...   Feb 22 2013, 22:48
||||||||- - John_Siau   QUOTE (greynol @ Feb 22 2013, 16:48) Is t...   Feb 22 2013, 22:57
||||||||- - greynol   QUOTE (John_Siau @ Feb 22 2013, 13:57) Ye...   Feb 22 2013, 23:05
|||||||- - saratoga   QUOTE (Arnold B. Krueger @ Feb 22 2013, 17...   Feb 23 2013, 04:02
|||||||- - Arnold B. Krueger   QUOTE (saratoga @ Feb 22 2013, 22:02) Loo...   Feb 23 2013, 17:11
|||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 23 2013, 11...   Feb 27 2013, 15:10
|||||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 27 2013, 09:10) In...   Feb 27 2013, 16:30
||||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 27 2013, 10...   Mar 4 2013, 17:28
||||||||- - Soap   QUOTE (John_Siau @ Mar 4 2013, 11:28) QUO...   Mar 5 2013, 01:11
|||||||- - Nessuno   QUOTE (John_Siau @ Feb 27 2013, 15:10) Wh...   Feb 28 2013, 13:57
||||||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 15:13) An...   Feb 22 2013, 22:56
||||||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 16...   Feb 22 2013, 23:06
|||||- - greynol   QUOTE (scuttle @ Feb 22 2013, 10:01) That...   Feb 22 2013, 19:42
|||||- - Arnold B. Krueger   QUOTE (greynol @ Feb 22 2013, 13:42) QUOT...   Feb 22 2013, 20:36
|||||- - greynol   QUOTE (Arnold B. Krueger @ Feb 22 2013, 11...   Feb 22 2013, 20:43
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 09:15) Wr...   Feb 22 2013, 17:48
|||- - scuttle   QUOTE (saratoga @ Feb 21 2013, 22:23) QUO...   Feb 22 2013, 15:49
||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 17:03) QU...   Feb 22 2013, 16:10
||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 10...   Feb 22 2013, 19:41
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 21 2013, 16:00
||- - John_Siau   QUOTE (John_Siau @ Feb 20 2013, 16:52) Ta...   Feb 21 2013, 18:44
|||- - [JAZ]   QUOTE (John_Siau @ Feb 21 2013, 18:44) sy...   Feb 21 2013, 20:36
|||- - John_Siau   QUOTE ([JAZ] @ Feb 21 2013, 14:36...   Feb 21 2013, 22:49
|||- - [JAZ]   That the usual listening volume of most electronic...   Feb 21 2013, 23:45
|||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 16:49) QU...   Feb 22 2013, 16:27
|||- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 22 2013, 10...   Feb 22 2013, 18:17
|||- - John_Siau   The following quote from NwAvGuy's Sansa Clip+...   Feb 22 2013, 18:32
|||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 12:17) In...   Feb 22 2013, 18:40
||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 12:40) I...   Feb 22 2013, 19:10
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 13:10) QU...   Feb 22 2013, 19:45
||||- - John_Siau   QUOTE (saratoga @ Feb 22 2013, 13:45) I d...   Feb 22 2013, 20:38
||||- - saratoga   QUOTE (John_Siau @ Feb 22 2013, 14:38) QU...   Feb 22 2013, 20:42
|||- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 22 2013, 12:17) Bu...   Feb 22 2013, 20:58
|||- - saratoga   QUOTE (Arnold B. Krueger @ Feb 22 2013, 14...   Feb 22 2013, 21:07
|||- - Arnold B. Krueger   QUOTE (saratoga @ Feb 22 2013, 15:07) QUO...   Feb 22 2013, 23:01
||- - Ethan Winer   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 20:43
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 20 2013, 16:52) D/...   Feb 21 2013, 16:04
|- - John_Siau   QUOTE (Arnold B. Krueger @ Feb 21 2013, 10...   Feb 21 2013, 16:28
|- - Arnold B. Krueger   QUOTE (John_Siau @ Feb 21 2013, 10:28) QU...   Feb 21 2013, 18:28
- - Yahzi   So your view is that it is a potential issue but i...   Feb 20 2013, 23:09
- - saratoga   I think SNR is probably not the best way to think ...   Feb 22 2013, 00:05
- - greynol   Since when has NwAvGuy been the ultimate arbiter o...   Feb 22 2013, 18:53
|- - scuttle   QUOTE (greynol @ Feb 22 2013, 17:53) Sinc...   Feb 22 2013, 19:08
|- - greynol   QUOTE (scuttle @ Feb 22 2013, 10:08) You...   Feb 22 2013, 19:18
- - greynol   So rockbox uses the analog volume control, which i...   Feb 22 2013, 20:27
- - greynol   1) 6 dB is not 20 dB 2) Downward scaling in order...   Feb 22 2013, 21:30
- - Mach-X   Rather ironic that everybody is rather correct. Th...   Mar 5 2013, 11:47


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