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digital dc offset problem

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Anonymous
May 27, 2005 6:11:04 AM

Archived from groups: rec.audio.pro (More info?)

When i use the digital output of the A/D converter AD192 of the preamp
PRESONUS
EUREKA i get a DC offset that produce a low freq noise (about 0 to 10
hz)of -40 db . Is that normal ? Is the converter broken ? when i
connect the analog output
to my audio card there is no dc offset . To be sure that the problem is
only in the a/d converter of the presonus eureka i tried the digital
output with 2 audio card , the echo layla 24 and a soundblaster live ,
and i found the same problem .

More about : digital offset problem

Anonymous
May 27, 2005 11:53:26 AM

Archived from groups: rec.audio.pro (More info?)

The problem is that i get this noise without plug in into my preamp
input any
instrument . I get this noise when i turn on my audio card ,my preamp ,
and
i select the digital s/pdf input . About the freq of this noise is
close to 0 herz , and the intencity is highter close 0 hz and lower to
about 10 or 15 hz
( there is a gradual lowering level db from 0 hz to 10 hz )
If i analyze that noise with a spectrum analyzer i find a 100% dc
offset .
I can solve this problem using the "remove dc offset" of cubase sx ,
audition
or other audio software , or using an hi-pass filter to cut the lower
freq .
I can't ear this noise 'cause the audible human freq range ,but i can't
understant the origin of this noise ,it's really strange.
I'm thinkin about the unbalanced digital output .


Mike Rivers ha scritto:
> In article <1117185064.926513.181980@o13g2000cwo.googlegroups.com> lorvel@tiscali.it writes:
>
> > When i use the digital output of the A/D converter AD192 of the preamp
> > PRESONUS
> > EUREKA i get a DC offset that produce a low freq noise (about 0 to 10
> > hz)of -40 db . Is that normal ? Is the converter broken ?
>
> If it's 0-10 Hz, it's not DC offset. You just have some low frequency
> noise that's below the low frequency cutoff limit of your analog sound
> card.
>
> As an experiment, you can make a "dummy mic" from an XLR plug with
> pins 2 and 3 connected together. (some people prefer a 150 ohm
> resistor instead of a short circuit, but for this application, a short
> is probalby bettter) Plug that into the mic input and see if the noise
> goes away. If it does, you're seeing noise that your mic is picking
> up, just normal air movement noise. (this is why we have high-pass
> filters). If the noise doesn't go away, then it's in the circuitry. As
> to whether it's normal or not, that's for Presonus to decide.
>
> How are you measuring this noise? Since you mentioned a frequency
> range, I suspect that you might be applying a spectrum analyzer
> plug-in to a recording. Spectrum analyzer software tools usually lie
> at very low frequencies, so if that's how you're making your
> measuremnts, you may be seeing something that's not really there. If
> you're actually seeing a waveform in that frequency range, that's real
> noise, and probalby real if you're seeing it with a mic connected.
>
>
> --
> I'm really Mike Rivers (mrivers@d-and-d.com)
> However, until the spam goes away or Hell freezes over,
> lots of IP addresses are blocked from this system. If
> you e-mail me and it bounces, use your secret decoder ring
> and reach me here: double-m-eleven-double-zero at yahoo
Anonymous
May 27, 2005 1:22:54 PM

Archived from groups: rec.audio.pro (More info?)

In article <1117185064.926513.181980@o13g2000cwo.googlegroups.com> lorvel@tiscali.it writes:

> When i use the digital output of the A/D converter AD192 of the preamp
> PRESONUS
> EUREKA i get a DC offset that produce a low freq noise (about 0 to 10
> hz)of -40 db . Is that normal ? Is the converter broken ?

If it's 0-10 Hz, it's not DC offset. You just have some low frequency
noise that's below the low frequency cutoff limit of your analog sound
card.

As an experiment, you can make a "dummy mic" from an XLR plug with
pins 2 and 3 connected together. (some people prefer a 150 ohm
resistor instead of a short circuit, but for this application, a short
is probalby bettter) Plug that into the mic input and see if the noise
goes away. If it does, you're seeing noise that your mic is picking
up, just normal air movement noise. (this is why we have high-pass
filters). If the noise doesn't go away, then it's in the circuitry. As
to whether it's normal or not, that's for Presonus to decide.

How are you measuring this noise? Since you mentioned a frequency
range, I suspect that you might be applying a spectrum analyzer
plug-in to a recording. Spectrum analyzer software tools usually lie
at very low frequencies, so if that's how you're making your
measuremnts, you may be seeing something that's not really there. If
you're actually seeing a waveform in that frequency range, that's real
noise, and probalby real if you're seeing it with a mic connected.


--
I'm really Mike Rivers (mrivers@d-and-d.com)
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me here: double-m-eleven-double-zero at yahoo
Related resources
Anonymous
May 29, 2005 1:01:26 PM

Archived from groups: rec.audio.pro (More info?)

I got the same dc offset problem when transferring tracks between
computers. Turned out the problem was in my MAudio dio2496's spdif
out... Quit using that and away the problem went. It was not an analog
issue btw since it always happened on the cards spidf out regardless of
routing.

When playing source files through it, they always had 100% dc offset.

Maybe a hosed spdif transmitter?
Anonymous
May 29, 2005 1:09:00 PM

Archived from groups: rec.audio.pro (More info?)

"Roger F" wrote ...
>I got the same dc offset problem when transferring tracks between
> computers. Turned out the problem was in my MAudio dio2496's spdif
> out... Quit using that and away the problem went. It was not an analog
> issue btw since it always happened on the cards spidf out regardless
> of
> routing.
>
> When playing source files through it, they always had 100% dc offset.

A "100% DC offset" would be full-scale DC! No sound at all.

> Maybe a hosed spdif transmitter?

Unlikely. More like something screwy in a driver somewhere.
Are you using the latest drivers?
Anonymous
May 30, 2005 4:08:47 PM

Archived from groups: rec.audio.pro (More info?)

Richard Crowley wrote:
> "Roger F" wrote ...
> >I got the same dc offset problem when transferring tracks between
> > computers. Turned out the problem was in my MAudio dio2496's spdif
> > out... Quit using that and away the problem went. It was not an analog
> > issue btw since it always happened on the cards spidf out regardless
> > of
> > routing.
> >
> > When playing source files through it, they always had 100% dc offset.
>
> A "100% DC offset" would be full-scale DC! No sound at all.
>
> > Maybe a hosed spdif transmitter?
>
> Unlikely. More like something screwy in a driver somewhere.
> Are you using the latest drivers?

I used all their drivers.... Same result. I meant 10% btw. Finally
boxed the maudio card and installed MOTU i/o hardware, and all is well.

It is most likely hardware, since it does it regardless of drivers (or,
non-drivers in the case of the pathetic midiman stuff)
Anonymous
May 31, 2005 5:15:42 PM

Archived from groups: rec.audio.pro (More info?)

Roger F wrote:
> Richard Crowley wrote:
>> "Roger F" wrote ...
>>> I got the same dc offset problem when transferring
tracks between
>>> computers. Turned out the problem was in my MAudio
dio2496's spdif
>>> out... Quit using that and away the problem went. It was
not an
>>> analog issue btw since it always happened on the cards
spidf out
>>> regardless of
>>> routing.

What different receivers did you have?

>>> When playing source files through it, they always had
100% dc
>>> offset.
>>
>> A "100% DC offset" would be full-scale DC! No sound at
all.
>>
>>> Maybe a hosed spdif transmitter?
>>
>> Unlikely.

Agreed, unlikely. SP/DIF hardware is like most things that
are pure digital - they either work perfectly or very badly.
A 10% DC offset doesn't fit into either category, so it is
unlikely to be a hardware problem.

>> More like something screwy in a driver somewhere.
>> Are you using the latest drivers?

> I used all their drivers.... Same result. I meant 10% btw.
Finally
> boxed the maudio card and installed MOTU i/o hardware, and
all is
> well.

> It is most likely hardware, since it does it regardless of
drivers
> (or, non-drivers in the case of the pathetic midiman
stuff)

IME, MIDIMan's drivers seem to be pretty good.
!