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DAC that handles intersample overs
krabapple
post Oct 23 2012, 16:32
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I was tipped off to this on an audio mailing list and thought it might be of interest here -- Benchmark has released a consumer DAC that (among other features) allows 3.5dB of headroom to account for correct reconstruction of intersample overs (peaks between samples that exceed 0dbFS, which are said to be "common in commercial releases")


http://www.benchmarkmedia.com/dac/dac2-hgc


QUOTE
High Headroom DSP - with 3.5 dB "Excess" Digital Headroom
All of the digital processing in the DAC2 HGC is designed to handle signals as high as +3.5 dBFS. Most digital systems clip signals that exceed 0 dBFS. The 0 dBFS limitation seems reasonable, as 0 dBFS is the highest sinusoidal signal level that can be represented in a digital system. However, a detailed investigation of the mathematics of PCM digital systems will reveal that inter-sample peaks may reach levels slightly higher than +3 dBFS while individual samples never exceed 0 dBFS. These inter-sample overs are common in commercial releases, and are of no consequence in a PCM system until they reach an interpolation process. But, for a variety of reasons, virtually all audio D/A converters use an interpolation process. The interpolation process is absolutely necessary to achieve 24-bit state-of-the art conversion performance. Unfortunately, inter-sample overs cause clipping in most interpolators. This clipping produces distortion products that are non-harmonic and non-musical . We believe these broadband distortion products often add a harshness or false high-frequency sparkle to digital reproduction. The DAC2 HGC avoids these problems by maintaining at least 3.5 dB of headroom in the entire conversion system. We believe this added headroom is a groundbreaking improvement.



disclaimer: i neither work for Benchmark nor own a Benchmark DAC ;> Claims about reduced 'high frequency sparkle' taken with a grain of salt.

This post has been edited by krabapple: Oct 23 2012, 16:33
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2Bdecided
post Oct 24 2012, 15:22
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@RonaldDumsfeld, many modern pop CDs are near clipping most of the time (whether the waveform is cut off at 0dB FS or some fraction of a dB below it is irrelevant). Inter-sample overs are inevitable. clipping after mp3 encoding+decoding is inevitable. (unless you reduce the level or increase the headroom at the right point in each case).

The audibility of mp3-induced clipping is rare (I've seen one positive ABX on here), but it's entirely avoidable.

The audibility of the damaged inflicted by the mastering practices that create these kind of recordings on CD is hard to ABX (we have no "before" - and when we do, it sounds obviously different anyway) - but my guess would be that far more damage is done at this stage than in mp3 clipping or inter-sample over clipping.


Your meters can only guess. They typically go red when they see single or multiple samples at full scale. they don't actually know if the waveform should/did go above full scale. they just guess that (multiple) samples at full scale mean it much have. That's usually true, but you can have samples way below full scale that cause inter-sample overs. It takes more sophisticated metering to catch this, though it exists (it's discussed in EBU R-128, amongst others).

Cheers,
David.
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greynol
post Oct 24 2012, 15:32
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QUOTE (2Bdecided @ Oct 24 2012, 07:22) *
The audibility of mp3-induced clipping is rare (I've seen one positive ABX on here), but it's entirely avoidable.

Real music or a synthetic sample? I've continually asked for real-world evidence for this as people regularly take measures to prevent it. They often get quite testy when I suggest they are just being paranoid. Whenever I demand proof I am often assured some will be given in the near future and it never is.

EDIT: I am assured -> I am often assured. Anyway, I really don't want to make hay of this here. I too recall reading about it once, perhaps in addition to the link lvqcl will give three posts down, though I will have to review it before I am personally satisfied.

This post has been edited by greynol: Oct 24 2012, 18:30


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2Bdecided
post Oct 24 2012, 16:46
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QUOTE (greynol @ Oct 24 2012, 15:32) *
QUOTE (2Bdecided @ Oct 24 2012, 07:22) *
The audibility of mp3-induced clipping is rare (I've seen one positive ABX on here), but it's entirely avoidable.

Real music or a synthetic sample? I've continually asked for real-world evidence for this as people regularly take measures to prevent it. They often get quite testy when I suggest they are just being paranoid. Whenever I demand proof I am assured some will be given in the near future and it never is.
I thought I PM'd you when I saw it - or at least mentioned your name in a reply to the post - I remembered your long-standing request when it came up. But search can't find it, so maybe I was dreaming.

Cheers,
David.
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Posts in this topic
- krabapple   DAC that handles intersample overs   Oct 23 2012, 16:32
- - greynol   QUOTE (krabapple @ Oct 23 2012, 08:32) We...   Oct 23 2012, 17:36
- - RonaldDumsfeld   I wonder how they do it? How can you represent a v...   Oct 23 2012, 19:20
|- - Arnold B. Krueger   QUOTE (RonaldDumsfeld @ Oct 23 2012, 14:2...   Oct 23 2012, 20:25
|- - Arnold B. Krueger   QUOTE (RonaldDumsfeld @ Oct 23 2012, 14:2...   Oct 26 2012, 15:12
|- - pbelkner   QUOTE (Arnold B. Krueger @ Oct 26 2012, 15...   Oct 27 2012, 05:56
- - DVDdoug   QUOTE I wonder how they do it? How can you represe...   Oct 23 2012, 20:15
- - AndyH-ha   The DAC's output is an analogue voltage swing....   Oct 23 2012, 22:07
|- - Arnold B. Krueger   QUOTE (AndyH-ha @ Oct 23 2012, 17:07...   Oct 24 2012, 13:51
- - [JAZ]   There are several sentences that sound strange to ...   Oct 23 2012, 22:17
- - Wombat   I am absolutely no expert at this but may it be as...   Oct 23 2012, 22:30
- - AndyH-ha   Considering the general state of decent hardware, ...   Oct 23 2012, 23:16
|- - Arnold B. Krueger   QUOTE (AndyH-ha @ Oct 23 2012, 18:16...   Oct 24 2012, 13:59
- - pdq   Upsampling would involove multiplying a set of dat...   Oct 24 2012, 10:55
- - RonaldDumsfeld   I know the OP is talking about inter sample overs ...   Oct 24 2012, 13:13
|- - pbelkner   QUOTE (RonaldDumsfeld @ Oct 24 2012, 13:1...   Oct 24 2012, 15:45
- - 2Bdecided   @RonaldDumsfeld, many modern pop CDs are near clip...   Oct 24 2012, 15:22
|- - greynol   QUOTE (2Bdecided @ Oct 24 2012, 07:22) Th...   Oct 24 2012, 15:32
|- - 2Bdecided   QUOTE (greynol @ Oct 24 2012, 15:32) QUOT...   Oct 24 2012, 16:46
- - lvqcl   Probably this - http://www.hydrogenaudio.org/foru...   Oct 24 2012, 17:00
- - Speedskater   A sometimes technical and sometimes not E-mail gro...   Oct 24 2012, 18:06
- - gymnos   some of the topics of this discussion were covered...   Oct 24 2012, 21:47
|- - krabapple   Yes, but that work is a decade old. Are pro DACs ...   Oct 25 2012, 05:37
- - RonaldDumsfeld   QUOTE Could you give r128gain a try? I'd love...   Oct 25 2012, 15:31
|- - pbelkner   QUOTE (RonaldDumsfeld @ Oct 25 2012, 15:3...   Oct 25 2012, 16:19
- - RonaldDumsfeld   ^^ I'd already done that. It opens a command ...   Oct 25 2012, 18:42
- - Wombat   I wonder if these inter-sample peaks are a problem...   Oct 27 2012, 16:55
|- - pbelkner   QUOTE (Wombat @ Oct 27 2012, 16:55) I won...   Oct 27 2012, 18:08
- - lvqcl   Several posts in this thread are relevant to this ...   Oct 27 2012, 19:22
- - bandpass   Sounds like this DAC is just what I need for my am...   Oct 27 2012, 19:45
- - Dynamic   Thomas Lund has measured intersample over distorti...   Oct 28 2012, 01:12


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