Home Computer Audio Asylum

Music servers and other computer based digital audio technologies.

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Computer Audio Asylum ]
[ Alert Moderator ]

cics' web site - jitter and upsampling

I had a quick look at cics web site, and read the articles on jitter and building computer transports.

The article on jitter is not bad, I pretty much agree with it, although I think's cics' claims around measuring jitter must be taken with a grain of salt. The J-test doesn't actually measure jitter, it measures artefacts caused by perturbing an audio signal, which *may* be due to jitter.

In terms of "The Art of Building Computer Transports", I'm afraid I don't really agree with the article. cics's justification for why an upsampler is a good idea is incorrect. It stems from a common misunderstanding about digital sampling - "oh look, if I plot the discrete samples on a graph and join straight lines between them, the resultant waveform looks really bad and artificial!!! upsampling fixes this !!!!"

The reality is that Nyquist's theorem guarantees that when the output of the DAC converting these discrete samples are then passed through a low pass filter, the original analog waveform is reconstructed perfectly (at least, for frequency components below the Nyquist frequency).

In fact, programs like Adobe Audition tries to dispel this myth by actually reconstructing the analog waveform when you zoom in to the actual samples - to prove to their users that it is possible to do a perfect reconstruction. What Adobe Audition does is exactly what the low-pass "analog reconstruction" filter does post DAC.

So, upsampling is not required. I personally believe upsampling actually damages the audio signal, because it is an unnecessary addition to the signal path, and no filter is perfect in the sense that it is truly "lossless" - since we already have an analog reconstruction filter the extra filter doesn't really add any value.

A lot of people believe an upsampler can potentially avoid a bad oversampling filter in the DAC. This is just not true for a modern flagship DAC, in which the over-sampler is applied only to the upper bits (where it doesn't do much "damage" no matter how poorly implemented it is) and the lower bits are converted to a delta-sigma modulated bitstream.

In this case, any upsampler, no matter how good it is, is at best just adding more noise (through filter quantization error) to the signal path.

This post is made possible by the generous support of people like you and our sponsors:
  Schiit Audio  

Follow Ups Full Thread
Follow Ups
FAQ

Post a Message!

 Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]