Clyde Slick wrote:

Its time to dredge out this old baby again!!

Here is a challenge for Graham:
A while ago Arnie got into a heated argument against John Atkinson
and Glenn Z regarding aspects of the J Test about whether or
not the signal should be dithered.
I would like you to revisit this issue and tell us whether
you think Arnie was correct, or if John and Glenn were correct.
Since you are on a similar level of technical expertise as
Glenn, I think your input into this matter
would be very helpful and interesting.
And a new discussion on the technical merits should
prove interesting, as well.

Here are some excerpts:

snipped for brevity

That's quite a meal you posted there Clyde. It raises a number of issues that
were doubtless once contentional but now likely to be rather less of an
isssue due to technical improvements in conversion.

I had to print out what you posted but I was still unclear who exactly was
commenting on whom.

I'll reply thus - hopefully it'll answer your questions - at least in part.


Use of dither.

Dither is essentially similar to adding noise to the signal to be quantised.
I have heard undithered digital audio at low bit depth at Neve ( where the
possibilities existed to research such stuff ) and it truly sounds awful.
Like a buzz-saw almost.

Use of a careful amount of dither introduces *new samples* that 'smooth out'
the reproduced waveform and provide a more acceptable result for human
listening.

That is a simpistic representation but essentially gives a workable overview.

As to whether you should use a dithered signal to test a D-A depends on which
characteristics you are seeking to measure. 'Horses for courses'.


Jitter.

The intelligent can deduce that jitter ( inaccuracy in the time domain ) can
be directly correlated as an equivalent error in the amplitude domain ( when
no attempt is made at jitter reduction ).

Early digital products sometimes experienced high levels of jitter. I was
involved in producing a report back in 1988 for the benefit of several
pro-audio manufacturers on this precise subject.

At worst, jitter can cause data recovery problems in the receiver of a serial
digital signal ( e.g AES or SPDIF format ) that may cause signal muting.

My investigations indicated that one specific Japanese pro-audio manufacturer
had a level of jitter that caused problems with much other digitally
interfaced equipment.

That specific Japanese manufacturer subsequently withdrew from the digital
pro-audio market.

Modern digital receivers have far 'cleverer' circuitry that can accomadate
jitter with more tolerance and reject it.

Does that help ?

Graham

p.s. the company that chose to withdraw from the digital pro-audio market is
also well known as a car manufacturer.