Dirty Digital [sic.]
 

tony sayer wrote:
In article , Eeyore rabbitsfriendsandrel
scribeth thus

tony sayer wrote:

Sure, I heard that - but it is absolutely minute. There is absolutely no
way that could cause interference to audio equipment in a studio. To
find it I had to make a pickup, use all the gain my DAT had on its mic
input, then apply another 20dB later.

I stood exactly where the arrow pointed.
Sure this isn't caused by earth currents anywhere appearing on say the
mains incomer and another earth like perhaps one for the studio "tech"
earth?..
In the kilohertz region ?

Graham


Could be. When I were a lad me and a mate managed to get a phone system
to work quite well over some hundreds of yards using spikes driven into
the ground several metres apart. Consider the Earth to be a large mass
of conducting matter of a varied resistance if you see what I mean.


I did exactly the same. Inspired by an article in Practical Wireless, I
seem to remember.

d

Dirty Digital [sic.]
 

On 2008-06-28, Jim Lesurf wrote:
In article , Phil Allison
wrote:
** Given that the only way to test a CD player's THD performance is by
the use of a special test signal CD

Which these days is easy enough to create for yourself if you know how to
generate dithered test waveforms and write them onto a CDR.

True. But there are still test CDs available from Philips, CBS etc.
A rather quick Google search reveals where these are for audio testing
rather than setting up the CD player mechanism they (some anyway) are
dithered for at least the low-level distortion test tracks.

Notably the CBS CD-1 test disk contains all of the test signals for the
ANSI/EIA-560-1990 CD testing standard. "The Comapact Disk Handbook" lists
the CBS CD-1 content (on page 179), notes that there are -70 dB to -100 dB
signals recorded with dither, and says "The use of dithered test signals
is crucial at low ampltudes because it would be otherwise impossible to
separate the player's distortion from those in the test signal itself".

I see that there are also some freely downloadable test disks
that appear to be fully dithered (or noise shaped). For example
http://www.lindos.co.uk/testcd2.html. Confirming the statement on
the web page that "Noise Shaping used on all tracks (unless stated)",
a quick spectral analysis of a couple of the tracks shows no trace of
undithered levels of quantization distortion.

FWIW The example spectra on the webpages I wrote use the form of data which
I do use with a CD burner to create CDRs for audio replay. I created data
files of the type I'd normally write to CDR, and then used the data for the
FFTs.

The danger of creating test CDs is the possibility of ignorance of
the test signals that you do need to dither. "A little learning is a
dangerous thing; Drink deep, or taste not the Pierian spring: ..."

BTW to create the spectra do you just apply the FFT or do you use one
of the power spectrum estimation techniques? I am never sure what's
best but I always do spectral analysis using Welch's periodogram method
with a Hanning window and then apply a very light "video filter".

--
John Phillips

Dirty Digital [sic.]
 

"Don Pearce" wrote in message
et...


Could be. When I were a lad me and a mate managed to get a phone system
to work quite well over some hundreds of yards using spikes driven into
the ground several metres apart. Consider the Earth to be a large mass
of conducting matter of a varied resistance if you see what I mean.


I did exactly the same. Inspired by an article in Practical Wireless, I
seem to remember.


And me (that article has much to answer for!)

All the early telegraph systems used the earth as the return conductor, as
did the very earliest telephone exchange systems. The conversion of
telephone exchanges to balanced line operation was as much due to problems
with noise in the earth return path (due in many cases to the proximity of
electric tramway systems) as it was to cross-talk between the single-wire
lines. Earth return telephone signalling systems continued in use right up
to the end of the analogue era.

David.

Dirty Digital [sic.]
 

"Jim Lesurf" wrote in message


I find it hard to fathom why he persistently follows the
same muddled line of his articles over many years. But I
suspect that it stems from a 'cart before horse' thought
process. This starts with his belief that CD inherently
and unavoidably has the alleged 'hard grey sound' and
then jumping onto what he reports as the 'reason'. Alas,
that approach seems classic with some people in audio.
Founded on a faith held as certainty, then 'factoids' are
assembled to provide (unreliable) 'support'. Shame.

John Atkinson has held tight to his practice of using undithered tones to
test digital equipment over in SP.

Both ragazines seem to have the same basic viewpoint of digital - it doesn't
sound like a LP so there must be something wrong with it. ;-(

Dirty Digital [sic.]
 

"Phil Allison" wrote in message

"Jim Lesurf"

Yes. I suspected he'd done that as a result of his
persistent use of undithered tones.


** Given that the only way to test a CD player's THD
performance is by the use of a special test signal CD -
kindly tell us who makes & where one can buy a test CD
that contains sine wave tones that are stated to have
been deliberately digitally dithered ?
AFAIK none of the professional test CDs sold by Philips
or Audio Technica or anyone else incorporated dithering
of the digitally generated 16 bit data strems that
constitute the sine wave test signals on the disk.

The AES has taken the position that all digital test tones used for testing
equipment must be dithered.

Makes a lot of sense to me.

Dirty Digital [sic.]
 

Arny Krueger wrote:
"Jim Lesurf" wrote in message


I find it hard to fathom why he persistently follows the
same muddled line of his articles over many years. But I
suspect that it stems from a 'cart before horse' thought
process. This starts with his belief that CD inherently
and unavoidably has the alleged 'hard grey sound' and
then jumping onto what he reports as the 'reason'. Alas,
that approach seems classic with some people in audio.
Founded on a faith held as certainty, then 'factoids' are
assembled to provide (unreliable) 'support'. Shame.

John Atkinson has held tight to his practice of using undithered tones to
test digital equipment over in SP.

Both ragazines seem to have the same basic viewpoint of digital - it doesn't
sound like a LP so there must be something wrong with it. ;-(



Does the Red Book have anything to say on the subject? I take the view
that dithering is a necessary and integral part of the A to D process.
Any test done without it is not a test of a player, merely a
demonstration of poor maths.

d

Dirty Digital [sic.]
 

"Arny Krueger" wrote in message
. ..
"Phil Allison" wrote in message

"Jim Lesurf"

Yes. I suspected he'd done that as a result of his
persistent use of undithered tones.


** Given that the only way to test a CD player's THD
performance is by the use of a special test signal CD -
kindly tell us who makes & where one can buy a test CD
that contains sine wave tones that are stated to have
been deliberately digitally dithered ?
AFAIK none of the professional test CDs sold by Philips
or Audio Technica or anyone else incorporated dithering
of the digitally generated 16 bit data strems that
constitute the sine wave test signals on the disk.

The AES has taken the position that all digital test tones used for
testing equipment must be dithered.

Makes a lot of sense to me.

Just as a quick experiment I used Cool Edit to generate a 1kHz tone
at -80dBFS and then amplify it by 74 dB. Cool Edit's own spectrum analyser
didn't show any harmonics above the noise floor. On listening to the signal
it was clearly noisy, but there were no apparent harmonics, so I conclude
that Cool Edit automatically dithers tones that it generates even though it
doesn't explicitly state that.

David.

Dirty Digital [sic.]
 

David Looser wrote:
"Arny Krueger" wrote in message
. ..
"Phil Allison" wrote in message

"Jim Lesurf"

Yes. I suspected he'd done that as a result of his
persistent use of undithered tones.

** Given that the only way to test a CD player's THD
performance is by the use of a special test signal CD -
kindly tell us who makes & where one can buy a test CD
that contains sine wave tones that are stated to have
been deliberately digitally dithered ?
AFAIK none of the professional test CDs sold by Philips
or Audio Technica or anyone else incorporated dithering
of the digitally generated 16 bit data strems that
constitute the sine wave test signals on the disk.
The AES has taken the position that all digital test tones used for
testing equipment must be dithered.

Makes a lot of sense to me.

Just as a quick experiment I used Cool Edit to generate a 1kHz tone
at -80dBFS and then amplify it by 74 dB. Cool Edit's own spectrum analyser
didn't show any harmonics above the noise floor. On listening to the signal
it was clearly noisy, but there were no apparent harmonics, so I conclude
that Cool Edit automatically dithers tones that it generates even though it
doesn't explicitly state that.

David.




I don't know how similar Cool Edit is to Audition, but in the latter you
can make choices about dither. What you do is generate the tone at 32
bit, then use the Edit/Convert sample type menu to bring it back to 16
bits. At that stage you can choose the dither type. It is quite
revealing. Here are flat, plus types A B and C.

http://81.174.169.10/odds/dithers.gif

d

Dirty Digital [sic.]
 

Don Pearce wrote:
Arny Krueger wrote:
"Jim Lesurf" wrote in message


I find it hard to fathom why he persistently follows the
same muddled line of his articles over many years. But I
suspect that it stems from a 'cart before horse' thought
process. This starts with his belief that CD inherently
and unavoidably has the alleged 'hard grey sound' and
then jumping onto what he reports as the 'reason'. Alas,
that approach seems classic with some people in audio.
Founded on a faith held as certainty, then 'factoids' are
assembled to provide (unreliable) 'support'. Shame.

John Atkinson has held tight to his practice of using undithered tones
to test digital equipment over in SP.

Both ragazines seem to have the same basic viewpoint of digital - it
doesn't sound like a LP so there must be something wrong with it. ;-(



Does the Red Book have anything to say on the subject? I take the view
that dithering is a necessary and integral part of the A to D process.
Any test done without it is not a test of a player, merely a
demonstration of poor maths.

d

I had (still have in fact) little idea of what you are all talking
about, but I have tried, and in trying came across the origin of the
word 'dither'. Something to do with vibration and cogs moving more
easily apparently.

I did like the bit about introducing dither in a digital audio context
to 'make the sound more analogue'. Really, just put a record on :-)

Rob

Dirty Digital [sic.]
 

"Arny Krueger"

The AES has taken the position that all digital test tones used for
testing equipment must be dithered.



** Wot

- just a mere 25 years later than they should have ?



..... Phil