IPB

Welcome Guest ( Log In | Register )

DAC that handles intersample overs
krabapple
post Oct 23 2012, 16:32
Post #1





Group: Members
Posts: 2274
Joined: 18-December 03
Member No.: 10538



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
Go to the top of the page
+Quote Post
 
Start new topic
Replies
bandpass
post Oct 27 2012, 19:45
Post #2





Group: Members
Posts: 326
Joined: 3-August 08
From: UK
Member No.: 56644



Sounds like this DAC is just what I need for my amp that goes to 11.
Go to the top of the page
+Quote Post
Dynamic
post Oct 28 2012, 01:12
Post #3





Group: Members
Posts: 821
Joined: 17-September 06
Member No.: 35307



Thomas Lund has measured intersample over distortion in many high end DACs he tested, according to this portion of his technical presentation in a YouTube video where he demonstrates intersample over distortion in a NAD C 520 playing a 11.025 kHz sinusoid constructed to produce continuous intersample overs, viewed on an oscilloscope.

However, he's addressing a lot of issues from the precautionary principle and the idea of preventive measures in audio production engineering, hence the reason for measuring distortion in iTunes AAC and playing the S "side" signal of M/S stereo decomposition, with the message (eventually) coming that use of lossy sources in production should be avoided, but is perfectly fine for distribution (it felt like a massive TOS8 violation for most of the video until that became clear!).

In other words this is all about measurability, not proving audibility, and having tried and failed to ABX digital clipping of a sample-or-two's duration once or twice in the past, I'm tempted to think that audibility is unlikely. It certainly pales against the clear audible damage done by the Loudness War.

Nonetheless, for good engineering design, since I saw this video while bearing EBU-R128 intersample peak measures in mind, I've also thought it's eminently sensible to design any oversampling DAC to incorporate a fixed attenuation during the upsampling phase, potentially compensated for by the analogue circuitry. The upsampling and reconstruction filtering is performed with many multiplications in any case in floating point or high-depth fixed point in DSP, so a fixed multiplication or scaling of the filter coefficients to provide maybe 2-6 dB of headroom above digital full scale to the rail voltage of the op-amp is potentially relatively easy.
Go to the top of the page
+Quote Post

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


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 20th September 2014 - 21:11