Sharp DSP notch filter

Eeyore wrote:

> Jon Kirwan wrote:
>
> > (3)  On what time scale do these events occur?
>
> For example when lights are switched. So the frequency of occurence could
> be anything.

Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
model ( reason for the difference not known ).

Graham

On May 21, 6:51&#4294967295;am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Nils wrote:
> > After reading the discussion I wonder:
>
> > Couldn't you simply connect a transformer to the mains, add a resistor
> > divider at the output to get the signal down and record the glitches?
>
> My front end will do all of that to get the levels right etc. The thing is,
> you don't seem to be able to see the glitches for the mains, we've already
> been looking. They must be quite small, or it's getting in via another
> route. If we knew the route it would be easy but this is the task, to find
> what the susceptibility is in a 35 year old product.
>
> If we had unrestricted access we could try one idea at a time but it won't
> be like that so we need to be prepared for various eventualities.
>
> > That way we could take a look at the data and see what happends on the
> > mains.
>
> > You're at a recording studio after all. Recording something shouldn't be
> > much of a problem. :-)
>
> They might object to losing their hard disk rack. We can record it on a
> laptop of course but real time would keep the client happier.
>
> Graham

Have you researched Dranetz gear?
http://www.dranetz-bmi.com/

On Thu, 21 May 2009 02:54:36 +0100, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
><snip>

Hi, Graham.  A thought crossed my mind and it leads to some questions.

(1)  I think you mention elsewhere "to find what the susceptibility is
in a 35 year old product."  Is this something that has started more
recently, then?  Or has it been going on for a long time and they are
only now noticing or otherwise deciding to deal with it?

(2)  Who else (or what other activities) occupy the building?

(3)  On what time scale do these events occur?

I had a situation, years ago, where a dental office moved into the
building on a different floor.  Turns out, they had an x-ray machine
and they used it, on occasion.  When they did, I'd get nice, narrow kV
spikes back on the AC line that fed us.  There was another weird one
where a nearby research facility (150' away) would turn on some of
their equipment and we'd see our ground (relative to theirs) jump 7kV.
The copper communications line was a mess during that transition.

In other words, have you also checked out what's new, who else is
doing what, nearby?

Jon

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>
>
>"miso@sushi.com" wrote:
>
>> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
>> > Nils wrote:
>> > > After reading the discussion I wonder:
>> >
>> > > Couldn't you simply connect a transformer to the mains, add a resistor
>> > > divider at the output to get the signal down and record the glitches?
>> >
>> > My front end will do all of that to get the levels right etc. The thing is,
>> > you don't seem to be able to see the glitches for the mains, we've already
>> > been looking. They must be quite small, or it's getting in via another
>> > route. If we knew the route it would be easy but this is the task, to find
>> > what the susceptibility is in a 35 year old product.
>> >
>> > If we had unrestricted access we could try one idea at a time but it won't
>> > be like that so we need to be prepared for various eventualities.
>> >
>> > > That way we could take a look at the data and see what happends on the
>> > > mains.
>> >
>> > > You're at a recording studio after all. Recording something shouldn't be
>> > > much of a problem. :-)
>> >
>> > They might object to losing their hard disk rack. We can record it on a
>> > laptop of course but real time would keep the client happier.
>>
>> Have you researched Dranetz gear?
>> http://www.dranetz-bmi.com/
>
>I know their kind of stuff and Schaffner EMC too but this work won't pay for
>that.

I get a feeling you have a lot of time for this project, but not a
large budget to work with? I would get a high quality USB audio
interface. Put a front end together for measuring line voltages and
have it record for a few days at the highest resolution/sampling
frequency. Cooledit is a very good program for analyzing the data.

I think this route is faster than try to get going with DSP
algorithms.

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
                     "If it doesn't fit, use a bigger hammer!"
--------------------------------------------------------------

Eeyore a �crit :
> 
> Eeyore wrote:
> 
>> Jon Kirwan wrote:
>>
>>> (3)  On what time scale do these events occur?
>> For example when lights are switched. So the frequency of occurence could
>> be anything.
> 
> Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
> model ( reason for the difference not known ).
> 
> Graham
> 

Just make a self oscillating (battery+relay) EMI generator and take it 
all over the place. With a bit of chance you'll quickly find the 
sensitive loop(s).

-- 
Thanks,
Fred.

"Fred Bartoli"

>
> Just make a self oscillating (battery+relay) EMI generator and take it all 
> over the place. With a bit of chance you'll quickly find the sensitive 
> loop(s).


** The lying, stuffed cartoon character already knows exactly what the  " 
sensitive loop " in the room is.

Like some white elephant standing in the corner -  it's the antique EMI 
mixing desk  !

Basic audio fact:

A virtual earth mixing buss  IS  an induction loop receiver  !!

Common sense studio rule:

" No AC powered equipment is to be turned on off while recording is in 
progress. "


What a fucking crock of old shit the congenitally manic pommy charlatan is 
purveying now.

What a PITA scumbag.



....   Phil

On May 22, 1:44&#4294967295;pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> Nico Coesel wrote:
> > Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > >"m...@sushi.com" wrote:
> > >> Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:
> > >> > Nils wrote:
> > >> > > After reading the discussion I wonder:
>
> > >> > > Couldn't you simply connect a transformer to the mains, add a resistor
> > >> > > divider at the output to get the signal down and record the glitches?
>
> > >> > My front end will do all of that to get the levels right etc. The thing is,
> > >> > you don't seem to be able to see the glitches for the mains, we've already
> > >> > been looking. They must be quite small, or it's getting in via another
> > >> > route. If we knew the route it would be easy but this is the task, to find
> > >> > what the susceptibility is in a 35 year old product.
>
> > >> > If we had unrestricted access we could try one idea at a time but it won't
> > >> > be like that so we need to be prepared for various eventualities.
>
> > >> > > That way we could take a look at the data and see what happends on the
> > >> > > mains.
>
> > >> > > You're at a recording studio after all. Recording something shouldn't be
> > >> > > much of a problem. :-)
>
> > >> > They might object to losing their hard disk rack. We can record it on a
> > >> > laptop of course but real time would keep the client happier.
>
> > >> Have you researched Dranetz gear?
> > >>http://www.dranetz-bmi.com/
>
> > >I know their kind of stuff and Schaffner EMC too but this work won't pay for
> > >that.
>
> > I get a feeling you have a lot of time for this project, but not a
> > large budget to work with?
>
> Pretty much. I'm helping out a colleague who hasn't the funds for the expensive gear
> and can't design 'clever' electronics himself. The potential bonus for me is &#4294967295;that
> if we get it right we could be experts in the field. Ever lower noise levels mean
> more and more of this is surfacing.
>
> > I would get a high quality USB audio interface.
>
> I think he has something similar using firewire but there was something odd about
> it, would have to ask him again.
>
> > Put a front end together for measuring line voltages and
> > have it record for a few days at the highest resolution/sampling
> > frequency. Cooledit is a very good program for analyzing the data.
>
> > I think this route is faster than try to get going with DSP
> > algorithms.
>
> Could be done but I was very interested in the DSP route because of that real time
> processing advantage.
>
> Jan's idea interested me for example.http://panteltje.com/panteltje/xpequ/humfilter-0.1.tgzhttp://abelian.org/humfilt/
>
> Aside from not having a Linux box to run it on right now.
>
> Graham

You can always dual boot a windows PC. The Suse installer is pretty
smart regarding not messing with the other operating systems. I can't
see NOT having a linux box handy since there is so much open source
engineering software that runs under Linux. Sound on linux is hit and
miss. The program you mention uses OSS, which I think these days is
emulated via ALSA. Doing anything other than standard CD rate audio
can be problematic since all the drivers are 3rd party written by
volunteers. My current favorite soundcard for Linux is the Diamond
XS71. Cheap, fine performance, and works in many flavors of Linux.
Suse will sniff it and set it up as a C-Media chipset card. This one
will fall back to 8 bits if need be, which yeah, sounds bad in theory,
but a lot of the older programs used the 8 bit mode for communications
demodulation.

With a bit more skill, you could set up a live CD version of Suse or
whatever Linux you chose. The issue then would be to create the
ramdisk so you could install the software. I'm suspecting that would
be difficult. I don't know if the live CDs even have the compilers
installed, let alone the libraries.

The comb filter will only be "perfect" if the line frequency and
sample clock are phased locked.

On May 25, 10:10&#4294967295;pm, "m...@sushi.com" <m...@sushi.com> wrote:

> You can always dual boot a windows PC.

It can be quite a challenge for a non Unix wizzard to start using
Linux,
especially command line tools like humfilter.
As humfitler is a a simple command line program,.
written in a simple C, and basically only
does wav file format input to wave file output,
it should be easily portable to DOS, and run in
a MSDOS window in for example XP.
Perhaps compile with the old djgpp compiler?
Several of my programs have been ported to DOS by people.
I am sure you can somehow send the wave output to a soundcard
even in MS software.

   Here are my thoughts after reading the whole thread (I DID learn C
22 years ago - didn't make me rich, but it paid a lot more than
cleaning toilets in recording studios, and probably even more than
designing pro audio equipment).

In sci.electronics.design and comp.dsp, On Thu, 21 May 2009 02:54:36
+0100, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

>I am proposing to engage on a project regarding mains voltage 'purity'
>(and absence of ) with regard to audible clicks and pops in high-end
>professional and hi-fi audio equipment.
>
>Typical EMC filters operate in the RF band and are threfore no use to
>filter audio 'in band' noise that can travel through transformer
>interwinding capacitance etc.
>
>I have found some of the TI INA series that will with suitable
>preconditioning, tolerate mains voltages and give excellent common-mode
>etc rejection. So assembling a 'preamp' front end should be no problem.

   From what others posted, I'm thinking you might want to make
several of these, to also measure things like the neutral voltage and
the ground voltage (maybe referenced to your own ground stake you put
in the ground outside the window or door, on the opposite side of the
building where the main power comes in). Make these to withstand a
kilovolt or more on the inputs (use several series resistors in each
leg). That way you can see common-mode signals as well as
differential.

>
>What I will need to do however is to filter all the mains frequencies
>and harmonics to a very large degree.

   You say elsewhere you want to see the results in "real time." I
interpret that as "not having to wait 30 seconds for processing," that
a half-second or two seconds might be acceptable.

   Others have said it, but I also see this as a PC application. A USB
audio interface with four inputs should work (you probably want 24bit
samples - if USB can't do 48/24 and 4 channels, you then use a desktop
machine (or firewire, whatever), perhaps powered by a battery backup
to insure line isolation, with a 4=channel or 8-channel card). Three
inputs are for hot-to-neutral, neutral-to-your-ground,
ground-to-your-ground, and the forth is the balanced output (with
ground not connected!) of the mixer/console/UUT.

   You run this thing, and it samples data continuously. When the
mixer has an output (or when there's an anomalous output on any of the
other three inputs), the thing samples a few more cycles, then stops
and does the filtering (on data that's a few cycles long), and shows
the areas of interest, both with and without the 50/60Hz imposed on
the hot/neutral input.

   This puts all the algorithms in a PC which has plenty of DSP
horsepower thesedays, and also makes a good multichannel data
recorder. I'm thinking you (or someone who knows C and PC code
development) can get the Audacity source and modify it to do this (I
don't know of the legalities and such of using the code in a
commercial product, if you have to make the code you add open-source
or what).

   And you just might want to have more inputs to look at, such as the
main DC filtering caps of the console. This would show if the
transient occurs at a time when the rectifiers are conducting.

On Sat, 23 May 2009 01:25:25 +0100, Eeyore
<rabbitsfriendsandrelations@notmail.com> wrote:

>
>
>Eeyore wrote:
>
>> Jon Kirwan wrote:
>>
>> > (3)  On what time scale do these events occur?
>>
>> For example when lights are switched. So the frequency of occurence could
>> be anything.
>
>Just remembered that the air extractor in the 'loo' caused an audible transient too. That was fixed by replacement with another
>model ( reason for the difference not known ).

   Do you still have the old one? Will it make the same or similar
electrical noise if you just plug it in or unplug it from an outlet?
If not can you hook it back up to that same circuit and reproduce the
problem?  I'm thinking you really want to know the "reason for the
difference" in this case, or at least have an (extra) example of a
known-bad audible transient generator, to test how well any future fix
of the sound equipment works.

>
>Graham