Jim Lesurf wrote in
:

In article , Bob Latham
wrote:


"Jitter" may still be measurable on the incoming spdif signal, but
have no audible effects that a listener could show they heard if they
only have the sound to decide on.

A few people with really expensive gear beyond my pocket assured me
that jitter often a nightmare to get rid of.

That involves two properties of the people involved:

A) Own really expensive gear

B) Think jitter often a nightmare

Hard to say if (A) occurs for the same pre-existing reason as (B) rather
than their being a causal direct link... in either direction. :-)

This has set me wondering about the idea of writing a simple app that takes
an input wav file and applies a controlled amount of 'jitter'. Then allow
the user to repeatedly hear the same music with/without varying amounts so
they can decide for themself. That way they can use their own choice of
music though their own setups. If the app repeatedly applied/not the jitter
but kept a note without displaying it at the time, the user could then use
it to do 'blind tests' on themself and come to a conclusion.

Arny, have you or someone else done this already?

Slainte,

Jim


Jitter has a surprising effect in using audio outputs with DC blocking caps
renoved for DC coupling for laser projector galvo scan amp drive.

Never mind that this isn't audio, exactly. bear with me... While I had no
means to measure the jitter, the effects were dramatic. There is a standard
'ILDA test pattern' used for configuring scan systems. James Lehman, (coder
of software called LaserBoy) made me a WAV file version of this pattern,
which I used to help me assess some software experimenting of my own, and to
set up the Echo Layla 24/96 interface I was using.

Before I go further, I posted about that recently, I want to know if anyone
has tried one with a Via EPIA MII 12000 ITX mainboard. If so, please let me
know about it in reply to my post on the 20th of March.

Anyway, what I found was that this interface has two main driver variants,
one of them a WDM version. If you run this pattern without blanking the beam
so you see the draws as the beam is quickly positioned for the next drawn
element in the pattern, you can see a partial loop, like a bight of rope, as
it leaps from the bottom of the circle to a small vertical line drawn above
it. Scanner galvos have a lot of mass, they're like heavy duty fast moving-
magnet meters, and I don't know how much this relates to audio systems, but
it appears as if the resonance in a scanner being fixed, reacts with the
small timing errors in the non-WDM driver to form a dramatic and erratic
shift in the 'bight' formed by the scanners. It affects both axes, and the
vertical axis saw it shift in a range as great as 10 to 15 percent of full
scale.

How anyone interprets all this is up to them. I only mention it because it
happened, and I found it interesting. There is no doubt that removing jitter
makes the resonance play nice, but whether this would be important in sound
playback I don't know. I'd imagine that our hearing might react to it as
sight reacts to dither. It might even sound 'better' in many cases, if we
notice it at all.