I've started messing about with open mic recording and am having a gas with
all the usual humming, swearing, neighbour's lawnmower, birdsong etc.
accidental recordings but I'm also getting a little thump once in a while
which looks like this on the recording:

http://www.apah69.dsl.pipex.com/keith_g/show/glitch.jpg

It's very likely the thermostat or boiler which are both brand new and
therefore quite silent, so I haven't been able to catch it 'at it' yet but
what's mystifying me is why does it drag the waveform down which then takes
about a 1/4 of a second to recover? It's nothing like a scratch (or the
tower of crap the old boiler used to add in to the proceedings) and
therefore damn near impossible to remove!

Anyone got a clue what's happening?

In article ,
says...

http://www.apah69.dsl.pipex.com/keith_g/show/glitch.jpg

It's very likely the thermostat or boiler which are both brand new and
therefore quite silent, so I haven't been able to catch it 'at it' yet but
what's mystifying me is why does it drag the waveform down which then takes
about a 1/4 of a second to recover? It's nothing like a scratch (or the
tower of crap the old boiler used to add in to the proceedings) and
therefore damn near impossible to remove!

Anyone got a clue what's happening?

Someone or something treading on a capacitive mic cable ?


T.
--
Please Tony, NO!! You'd look dreadful in a basque and fishnets..

Sounds sorta like a large transient 'pulse' incoming from maybe local
switching thats putting an overly large signal onto your recording thats
depressing an autogain control circuit - the waveform coming up in 1/4 sec
is the recovery time. Thats guessing mind....

"Keith G" wrote in message
...
I've started messing about with open mic recording and am having a gas
with
all the usual humming, swearing, neighbour's lawnmower, birdsong etc.
accidental recordings but I'm also getting a little thump once in a while
which looks like this on the recording:

http://www.apah69.dsl.pipex.com/keith_g/show/glitch.jpg

It's very likely the thermostat or boiler which are both brand new and
therefore quite silent, so I haven't been able to catch it 'at it' yet but
what's mystifying me is why does it drag the waveform down which then
takes
about a 1/4 of a second to recover? It's nothing like a scratch (or the
tower of crap the old boiler used to add in to the proceedings) and
therefore damn near impossible to remove!

Anyone got a clue what's happening?

"Tony Gartshore" wrote in message
...
In article ,

says...

http://www.apah69.dsl.pipex.com/keith_g/show/glitch.jpg

It's very likely the thermostat or boiler which are both brand new and
therefore quite silent, so I haven't been able to catch it 'at it' yet
but
what's mystifying me is why does it drag the waveform down which then
takes
about a 1/4 of a second to recover? It's nothing like a scratch (or the
tower of crap the old boiler used to add in to the proceedings) and
therefore damn near impossible to remove!

Anyone got a clue what's happening?

Someone or something treading on a capacitive mic cable ?


Gawd, what does that mean then?

(Not sure anyone's walking on the cables when it happens though!)

"Mike Gilmour" wrote in message
. ..
Sounds sorta like a large transient 'pulse' incoming from maybe local
switching thats putting an overly large signal onto your recording thats
depressing an autogain control circuit - the waveform coming up in 1/4 sec
is the recovery time. Thats guessing mind....


Ok, I'll buy that - presumably the 'autogain control circuit' is in the mic,
Mike? (New component, new phenomenon....) But why/how is the waveform pulled
down from the 'centreline' or is that just a 'software thing'?

Here's another one.....

http://www.apah69.dsl.pipex.com/keit...ow/glitch2.jpg

......slightly different but showing the same general behaviour. The
waveform, while having been pulled down as before, appears to show no
reduction in gain (ie height of waveform).....

Or am I just reading this all wrong?

It's no biggie and has only happened a few times, but not being able to
'repair' it does mean that the recording (live joanna) has to be done again.
If it's the boiler (likely) the simplest remedy is prevention - like
switching it off, but my curiosity is what's happening with the waveform!

"Keith G" wrote in message
...

"Mike Gilmour" wrote in message
. ..
Sounds sorta like a large transient 'pulse' incoming from maybe local
switching thats putting an overly large signal onto your recording thats
depressing an autogain control circuit - the waveform coming up in 1/4
sec
is the recovery time. Thats guessing mind....


Ok, I'll buy that - presumably the 'autogain control circuit' is in the
mic,
Mike? (New component, new phenomenon....) But why/how is the waveform
pulled
down from the 'centreline' or is that just a 'software thing'?

Its not the mic, it looks more like the recovery of an amplifier circuit
thats had a sudden and gross overload - like walking into a wall when ****ed
and the time taken after to realise what happened ;-)

In article ,
Mike Gilmour wrote:
Ok, I'll buy that - presumably the 'autogain control circuit' is in
the mic, Mike? (New component, new phenomenon....) But why/how is the
waveform pulled down from the 'centreline' or is that just a 'software
thing'?

Its not the mic, it looks more like the recovery of an amplifier circuit
thats had a sudden and gross overload - like walking into a wall when
****ed and the time taken after to realise what happened ;-)

IMHO, a well designed mic amp that is relatively impervious to mains
splats etc isn't likely to be found outside good pro gear. And I wouldn't
trust any fitted to a PC sound card.

--
*Heart attacks... God's revenge for eating his animal friends

Dave Plowman London SW 12
RIP Acorn

"Mike Gilmour" wrote in message
...

"Keith G" wrote in message
...

"Mike Gilmour" wrote in message
. ..
Sounds sorta like a large transient 'pulse' incoming from maybe local
switching thats putting an overly large signal onto your recording
thats
depressing an autogain control circuit - the waveform coming up in 1/4
sec
is the recovery time. Thats guessing mind....


Ok, I'll buy that - presumably the 'autogain control circuit' is in the
mic,
Mike? (New component, new phenomenon....) But why/how is the waveform
pulled
down from the 'centreline' or is that just a 'software thing'?

Its not the mic, it looks more like the recovery of an amplifier circuit
thats had a sudden and gross overload - like walking into a wall when
****ed
and the time taken after to realise what happened ;-)


As if I would...... ;-)

Well, all I can say is I've had nothing like it before but I've not really
done any open mic recording before either. Perhaps it's in the computer
which is a cheapjack affair with only motherboard sound atm. I'll be
considering a decent soundcard suited to this sort of thing in the near
future if it takes off. (Any recommendations?)

"Keith G" wrote in message
...
I've started messing about with open mic recording and am having a gas
with
all the usual humming, swearing, neighbour's lawnmower, birdsong etc.
accidental recordings but I'm also getting a little thump once in a while
which looks like this on the recording:

http://www.apah69.dsl.pipex.com/keith_g/show/glitch.jpg

It's very likely the thermostat or boiler which are both brand new and
therefore quite silent, so I haven't been able to catch it 'at it' yet but
what's mystifying me is why does it drag the waveform down which then
takes
about a 1/4 of a second to recover? It's nothing like a scratch (or the
tower of crap the old boiler used to add in to the proceedings) and
therefore damn near impossible to remove!

Anyone got a clue what's happening?

How about an old refrigerator kicking in, and causing either a surge or
drain on the power supplied to whatever you've got your mic hooked up to?

When in college in the late 70s all the recordings I made - both in-line of
LPs and from a microphone - had an occasional warbled chirping noise that
wouldn't overdub the sounds being recorded, but rather sounded very lightly
in the background. Whether during a quiet spot in the recording or a Billy
Cobham drum solo, one could still hear this occasional weird sound that
lasted less than 1/4 of a second. It wasn't audible during the recording,
which was really weird. But it happened often enough that I sat and timed
the gaps between, and every time it was just between 12-13 minutes.

When I thought back on this - still thankfully having the fridge though no
longer at college several years later - I figured out timing the kicking in
of the compressor on the fridge. It was between 12-13 minutes, same as the
noise. I wasn't however experiencing the noise happening during recording
anymore - and put it down to the wiring in the dorm I was in at the time,
combined with the fridge kick-in and the Kenwood receiver I was taping
through during the entire span of time.

We didn't have surge protectors back then of course. One might wonder if
this would have been caught by one of the kind you can buy today for less
than 20 quid.

--
Steve Goodman
* Cartoons about DVDs and stuff
* http://www.earthlight.net/HiddenTrack
* (with links to Medialine)

On Sat, 5 Jun 2004 11:30:52 +0100, "Keith G"
wrote:

Ok, I'll buy that - presumably the 'autogain control circuit' is in the mic,
Mike? (New component, new phenomenon....) But why/how is the waveform pulled
down from the 'centreline' or is that just a 'software thing'?

The big pulse puts quite a hefty charge onto the input coupling
capacitor. The movement negative and subsequent recovery are simply
that charge leaking away again.

d
Pearce Consulting
http://www.pearce.uk.com