FA: Tara Labs Air 110 Digital XLR Cable * 3.3 Feet/1m NEW?
 

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.

FA: Tara Labs Air 110 Digital XLR Cable * 3.3 Feet/1m NEW?
 

In article ,
Lostgallifreyan

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

FWIW so far as I know correctly implimented spdif includes a transformer or
equivalent. Mainly to block loops and common mode, but it would also block
dc. So act similarly to a dc blocking cap IIRC.

[big snip]

Afraid I don't know what some of the terms you use like 'ILDA' and 'WDM'
mean in terms of the waveform details. However...

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.

My main interpetation is that the waveform shape 'as scanned' is altered.
That is the equivalent of saying 'jitter exists and can be caused by the
transmission system having a frequency response that isn't flat'. So not a
surprise.

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.

The significant point is that 'playback' requires a DAC which is clocked in
some way. If:

A) The DAC uses a clock that does *not* in the medium and short term depend
on the embedded pilot tone in the spdif.

B) The spdif 'jitter' is reasonably small compared with the bit-length
cycle

Then the 'jitter' on the signal is essentially suppressed by the 'replay'
system.

So you'd need to measure 'jitter' on the *output* from the *replay system*
- not just observe it on the spdif waveform - to assess the level so far
as any listener is concerned.

IIUC The systems you described drive the scanning directly, or by some
subsystem 'receiver' whose details are not clear to me from what you wrote.
In essence what you described would then be like looking at the spdif
waveform on a scope - not looking at the DAC output.

Hence like yourself I have no idea if what you say actually has any
relevance to the audio case.

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.

Alas the problem these is as I previously commented. Many things "might be
so", but only some of them (or none) *are so*. Indeed, imagining something
doesn't even show it is 'possible'... :-)

I don't doubt that at a suitably high level 'jitter' would be audible. Wow
and flutter if bad enough are easily audible. But that doesn't tell us if
what people claim is 'true'. :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

FA: Tara Labs Air 110 Digital XLR Cable * 3.3 Feet/1m NEW?
 

Jim Lesurf wrote in
:

In article ,
Lostgallifreyan

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

FWIW so far as I know correctly implimented spdif includes a transformer or
equivalent. Mainly to block loops and common mode, but it would also block
dc. So act similarly to a dc blocking cap IIRC.

[big snip]

Afraid I don't know what some of the terms you use like 'ILDA' and 'WDM'
mean in terms of the waveform details. However...

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.

My main interpetation is that the waveform shape 'as scanned' is altered.
That is the equivalent of saying 'jitter exists and can be caused by the
transmission system having a frequency response that isn't flat'. So not a
surprise.

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.

The significant point is that 'playback' requires a DAC which is clocked in
some way. If:

A) The DAC uses a clock that does *not* in the medium and short term depend
on the embedded pilot tone in the spdif.

B) The spdif 'jitter' is reasonably small compared with the bit-length
cycle

Then the 'jitter' on the signal is essentially suppressed by the 'replay'
system.

So you'd need to measure 'jitter' on the *output* from the *replay system*
- not just observe it on the spdif waveform - to assess the level so far
as any listener is concerned.

IIUC The systems you described drive the scanning directly, or by some
subsystem 'receiver' whose details are not clear to me from what you wrote.
In essence what you described would then be like looking at the spdif
waveform on a scope - not looking at the DAC output.

Hence like yourself I have no idea if what you say actually has any
relevance to the audio case.

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.

Alas the problem these is as I previously commented. Many things "might be
so", but only some of them (or none) *are so*. Indeed, imagining something
doesn't even show it is 'possible'... :-)

I don't doubt that at a suitably high level 'jitter' would be audible. Wow
and flutter if bad enough are easily audible. But that doesn't tell us if
what people claim is 'true'. :-)

Slainte,

Jim


Yes, there's a DAC in the Layla 24/96. (Is its main task). I noticed that the
WDM driver (Windows Driver Model) under Windows XP would make the 'bight' in
the scan even and stable. The point here is that the audio interface driver
itself (and perhaps the operating system's context for it) had small timing
errors. While you're talking of digital signals, the same might be true here
because the software driver has no clue whether the output would later be
digital or analog, yet the driver was clearly a source of jitter (because the
stable output of the WDM driver in WXP proved that the hardware wasn't), so I
assume a software driver could be so for a digital OR analog output in other
systems too.

No worries about the ILDA thing, the crucial point in that context (given for
completeness only) is that this occured during a very short moment, where a
mechanical system has to travel some largish chunk of full-scale deflection
in the duration of one or two samples. Note that the resonance is in no way
causal, not on its own anyway. I think it has to do with the timing over a
single sample duration varying in moderately large proportion to the nominal
sample rate. it might also be specific to the way a scanner amplifier uses
closed loop positional feedback, so maybe could only show up in an audio
speaker if it also used high output drive and a servo-type system to attempt
to get high tracking of an input waveform. Such systems exist but I don't
think many people use them. (Must cost a lot..)

Anyway, my smoke is in danger of masking any fire, I just added this stuff
because I thought it might help give a usefully different perspective on an
actual case of jitter. As the hardware is a professional high-end recording
system used in many studios during its time, I doubt that jitter had any
adverse effect on its sound. I never had any clue it was there till a
scanning galvo pair showed it to me.

FA: Tara Labs Air 110 Digital XLR Cable * 3.3 Feet/1m NEW?
 

"Jim Lesurf" wrote in message

In article ,
Lostgallifreyan

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

FWIW so far as I know correctly implimented spdif
includes a transformer or equivalent. Mainly to block
loops and common mode, but it would also block dc. So act
similarly to a dc blocking cap IIRC.

Generally the transformer also functions as a low pass filter, and helps
with passing USA FCC Part 15 EMI regulations. Bandpass is around 12 MHz.