Why is the desk doing this ?

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

Hi,

I'm still very much a newbie to mixing desks and encountered a problem
at last week's band practice that I can't work out.

Why is it, with the band all connected to the channel strips,
everyone's input trim set correctly, that when I hit the PFL button on
the Left submix fader, the PFL meter is hitting maximum. (all
channels are panned left as I'm only using a mono setup).

If I PFL any of the input channels, the meter tops out at 0dB.

I don't get it. I was expecting the PFL of the submix to be within
the 0dB limit I'd set for each of the input channels.


(That's my main question, but whilst I'm here... ;-) ).....

I discovered the PFL on the Left submix was too high whilst trying to
resolve why the minidisc recording I was making of us was distorted to
hell. The way we're set up is a bit odd due to equipment restraints,
but it works. Everyone plugs into the desk, panned left, I take the
Left submix out into a cable with an attenuator built into the XLR
end, this plugs into a mic input on our old 'PA head' (basic powered
mixer). [the attenuator works fine and we get good sound from the
mains]. The 'pa head' has a tape in/out and I connected the minidisc
to this. The powered monitors are just taken straight from the
monitor out on the desk.

I set everyone's input trims to peak at 0dB, set the Left submix fader
to 0dB, the input gain on the 'pa head' mic channel to midway, the
tape out level to midway and the recording level on the minidisc to
keep the meter on it out of the red. Like this, I get an obviously
overloaded signal recorded on the minidisc.

All I can tell you is that the sound from the mains didn't sound
distorted, nor the monitors, yet I got a distorted recording. Could
the tape out level be too high, distorting the input circuitry of the
MD - yet still see normal levels on the MD display ?

It was about then that I discovered the PFL level on the desk was off
the scale - I know that's not right, but I can't work out why, how,
where etc.... or if it's even related.

I know I'm gonna kick myself when one of you points it out (hopefully
!)

Any help will be much appreciated.

Cheers,

Kev.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

<pcmangler@ntlworld.com> wrote in message
news:rafpe1p19q02mki2nn0n38msi6pntdu4ds@4ax.com...
> Hi,
>
> I'm still very much a newbie to mixing desks and encountered a problem
> at last week's band practice that I can't work out.
>
> Why is it, with the band all connected to the channel strips,
> everyone's input trim set correctly, that when I hit the PFL button on
> the Left submix fader, the PFL meter is hitting maximum. (all
> channels are panned left as I'm only using a mono setup).
>
> If I PFL any of the input channels, the meter tops out at 0dB.
>
> I don't get it. I was expecting the PFL of the submix to be within
> the 0dB limit I'd set for each of the input channels.


By doing so, you've merely enabled the electronics in the individual channel
strips to process signals at optimum levels. What signal level a console's
buss will see still depends on how much you push the faders. It's quite easy
to overload a console's buss despite the proper gain-staging on the
individual channels. Especially on cheaper consoles.

Predrag




>
>
> (That's my main question, but whilst I'm here... ;-) ).....
>
> I discovered the PFL on the Left submix was too high whilst trying to
> resolve why the minidisc recording I was making of us was distorted to
> hell. The way we're set up is a bit odd due to equipment restraints,
> but it works. Everyone plugs into the desk, panned left, I take the
> Left submix out into a cable with an attenuator built into the XLR
> end, this plugs into a mic input on our old 'PA head' (basic powered
> mixer). [the attenuator works fine and we get good sound from the
> mains]. The 'pa head' has a tape in/out and I connected the minidisc
> to this. The powered monitors are just taken straight from the
> monitor out on the desk.
>
> I set everyone's input trims to peak at 0dB, set the Left submix fader
> to 0dB, the input gain on the 'pa head' mic channel to midway, the
> tape out level to midway and the recording level on the minidisc to
> keep the meter on it out of the red. Like this, I get an obviously
> overloaded signal recorded on the minidisc.
>
> All I can tell you is that the sound from the mains didn't sound
> distorted, nor the monitors, yet I got a distorted recording. Could
> the tape out level be too high, distorting the input circuitry of the
> MD - yet still see normal levels on the MD display ?
>
> It was about then that I discovered the PFL level on the desk was off
> the scale - I know that's not right, but I can't work out why, how,
> where etc.... or if it's even related.
>
> I know I'm gonna kick myself when one of you points it out (hopefully
> !)
>
> Any help will be much appreciated.
>
> Cheers,
>
> Kev.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

pcmangler@ntlworld.com wrote:

> Hi,
>
> I'm still very much a newbie to mixing desks and encountered a problem
> at last week's band practice that I can't work out.
>
> Why is it, with the band all connected to the channel strips,
> everyone's input trim set correctly,

How do you set it ?

> that when I hit the PFL button on
> the Left submix fader, the PFL meter is hitting maximum. (all
> channels are panned left as I'm only using a mono setup).
>
> If I PFL any of the input channels, the meter tops out at 0dB.
>
> I don't get it. I was expecting the PFL of the submix to be within
> the 0dB limit I'd set for each of the input channels.

Where on the dB scale are your channel and master faders set ?

If they're not around the 0dB mark that'll be why you're seeing high pfl
levels.

What is the maximum level of the pfl meter ? Some old desks only had
metering up to +3. There's likely 15dB headroom left at that point.

Graham

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

"Predrag Trpkov" <predrag.trpkovNeSpamu@ri.htnet.hr> wrote in message
newsciio8$psl$1@ss405.t-com.hr...
>
> <pcmangler@ntlworld.com> wrote in message
> news:rafpe1p19q02mki2nn0n38msi6pntdu4ds@4ax.com...
> > Hi,
> >
> > I'm still very much a newbie to mixing desks and encountered a problem
> > at last week's band practice that I can't work out.
> >
> > Why is it, with the band all connected to the channel strips,
> > everyone's input trim set correctly, that when I hit the PFL button on
> > the Left submix fader, the PFL meter is hitting maximum. (all
> > channels are panned left as I'm only using a mono setup).
> >
> > If I PFL any of the input channels, the meter tops out at 0dB.
> >
> > I don't get it. I was expecting the PFL of the submix to be within
> > the 0dB limit I'd set for each of the input channels.
>
>
> Pull the channel faders down a bit. You're overloading the left submix
buss,
> partly due to the panning. Depending on the pan law, the channel output
> level is a few dB higher (3-6 dB, typically) when panned hard left or
right,
> compared to the center position.
>

And also summing the channels. The more channels you use the lower each
individual channel gain has to be to end up with a 0 reading on the mains.
I haven't had much sleep this weekend and have not been thinking clearly so
maybe someone can give the correct LOG formula for finding the correct
setting for the individual channels based on the number of channels used.

Mike D.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

Mike Dobony wrote:
> And also summing the channels. The more channels you use the lower each
> individual channel gain has to be to end up with a 0 reading on the mains.

> maybe someone can give the correct LOG formula for finding the correct
> setting for the individual channels based on the number of channels used.

Assuming (rashly!) that they are all adjusted to the same RMS sound
level the sum (rms voltage) will be increased by the square root of the
number of channels added to the mix.

In dB, that's +3dB for each doubling of no. of channels.

Anahata

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

On 02/08/05 16:56, in article 11ev2dq13hivhda@corp.supernews.com, "Frank
Stearns" <franks.pacifier.com@pacifier.net> wrote:

(...)
> Also, a few replies suggested "pulling down the faders" a bit. They
> perhaps meant reducing the input trim (which would then mess up the gain
> structure if already optimal). If indeed this is a PFL (**PRE** fade
> listen) buss, changing the channel fader won't change the PFL level.

No, that's BS. We meant pull the faders down. The OP said, that the PFL of
the channels is at 0db, and the PFL of the submaster is way over. The PFL of
the submaster will show you what you have pre submaster fader, which is post
channel faders. So yes, changing the channel fader WILL change the submaster
PFL level.

NB: "submaster" in this context can be replaced by "group" or "master" or
whatever.


--
Joe Kotroczo kotroczo@mac.com

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

Joe Kotroczo <kotroczo@mac.com> writes:

>On 02/08/05 16:56, in article 11ev2dq13hivhda@corp.supernews.com, "Frank
>Stearns" <franks.pacifier.com@pacifier.net> wrote:

>(...)
>> Also, a few replies suggested "pulling down the faders" a bit. They
>> perhaps meant reducing the input trim (which would then mess up the gain
>> structure if already optimal). If indeed this is a PFL (**PRE** fade
>> listen) buss, changing the channel fader won't change the PFL level.

>No, that's BS. We meant pull the faders down. The OP said, that the PFL of
>the channels is at 0db, and the PFL of the submaster is way over. The PFL of
>the submaster will show you what you have pre submaster fader, which is post
>channel faders. So yes, changing the channel fader WILL change the submaster
>PFL level.

>NB: "submaster" in this context can be replaced by "group" or "master" or
>whatever.

Sorry; I missed that he was touching PFL on a group master. Indeed PFL
here would be what was coming into the group, so pulling back the faders
on the various channels assigned to that group would reduce the PFL (and
program) signal. PFL here would be in front of the group fader.

So then there's a question about the group level -- was the program level
of the group hot as well? Was the group fader quite a ways down from
unity, say 10 dB or more? In that case a PFL touch might blast you pretty
good, and it might be time to go back and retrim the input channels,
channel fader and if need be input trim.

Frank Stearns
Mobile Audio
--
.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

In article <dcm6tj$ig0$1@news.netins.net>,
"Mike Dobony" <sword@asarian-hostspamnot.net> wrote:

> And also summing the channels. The more channels you use the lower each
> individual channel gain has to be to end up with a 0 reading on the mains.
> I haven't had much sleep this weekend and have not been thinking clearly so
> maybe someone can give the correct LOG formula for finding the correct
> setting for the individual channels based on the number of channels used.


Summing of incoherent signals- 3dB for every doubling of open channels
Summing of phase coherent signals- 6dB for every doubling of open
channels. chances are, that vast majority of your sources incoherent.
And it is unlikely that any given time, that all channels will be at the
same (relative) level to your mix buss.

You don't need to calculate anything if you can PFL your submaster or
mix buss. What you can do, is run your master fader at unity, and AFL
the output. If you find that you are overdriving the mix buss, either
attenuate channel faders, or back down your trims a hair.

You don't need to make this a mental science project. Just watch how
hard you drive the mix buss, and compensate if necessary.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

On Sun, 31 Jul 2005 16:00:40 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

>pcmangler@ntlworld.com wrote:
>
>> Hi,
>>
>> I'm still very much a newbie to mixing desks and encountered a problem
>> at last week's band practice that I can't work out.
>>
>> Why is it, with the band all connected to the channel strips,
>> everyone's input trim set correctly,
>
>How do you set it ?

Plug 'em in, get the relevant person to give their instrument a good
thrashing (with any instrument volume set to max), trim the input on
the channel so it's just hitting 0dB on the PFL meter.

>Where on the dB scale are your channel and master faders set ?

0dB

>What is the maximum level of the pfl meter ? Some old desks only had
>metering up to +3. There's likely 15dB headroom left at that point.

Can't remember, the desk isn't here right now, but it's definitely
more than 3dB - +9 maybe ?



>On Mon, 01 Aug 2005 15:15:40 +1000, Joe Mama <bloodywanker@drugsmakemecool.com> wrote:

>Just curious: is there a specific reason why you're taking the feed from
>the 'pa head' for the minidisc? Why not from the right channel of the
>mixer? You could then bypass the (probably questionable) circuitry in
>the PA head, and also use the panpots for some finer tweaking of the mix
>to the minidisc without changing the sound in the room.


Funny you should suggest that, as that's what I did at the following
practice (before reading your post !). Got a much better result.
As for using the panpots to tweak the mix 'without changing the sound
in the room' - How do you figure that ? I can see that I could use
the panpots to send e.g. more of a particular channel's signal to the
right buss and therefore the minidisc, but wont that simultaneously
reduce the signal level on the left buss - which is the feed for the
speakers ?


Oddly, I didn't seem to suffer the PFL overload last week though...

The more I think about it, the more I'm sure that when I had the
problem originally, adjusting the channel faders made no difference to
the submix PFL - I think at one point I had them all zeroed and was
still getting overloading. I didn't post this before as I couldn't
remember exactly and didn't want to throw a wildcard into the equation
! I'll check again on Sunday to see if I'm right or just losing the
plot ! :-)

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

On Tue, 02 Aug 2005 14:56:58 -0000, Frank Stearns
<franks.pacifier.com@pacifier.net> wrote:

>Also, a few replies suggested "pulling down the faders" a bit. They
>perhaps meant reducing the input trim (which would then mess up the gain
>structure if already optimal). If indeed this is a PFL (**PRE** fade
>listen) buss, changing the channel fader won't change the PFL level.

I find it difficult to imagine that anyone who has ever had hands on a
mixing desk would say "pull down the faders" when he meant "adjust the
channel trim".

Don't forget PFL on a group is pre the group faders, but post the
channel faders routed to that group.

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

"Joe Kotroczo" <kotroczo@mac.com> wrote in message
news:BF1BF2CA.63A9%kotroczo@mac.com...
> On 06/08/05 14:30, in article 3ljl9bF132hc9U1@individual.net, "Phildo"
> <Phil@phildo.net> wrote:
>
>>> The more I think about it, the more I'm sure that when I had the
>>> problem originally, adjusting the channel faders made no difference to
>>> the submix PFL
>>
>> Hello?
>>
>> PFL - Pre Fader Listen !!!
>>
>> That's PRE, meaning "before".
>
> Phil, shouldn't the PFl of the group bus be pre group fader, but post
> channel faders?

Yes, but he was talking about the channels not the groups.

Phildo

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

"Geezer Sonics" <geeze@deafguy.com> wrote in message
news:geeze-C709F9.08130203082005@comcast.dca.giganews.com...
> In article <dcm6tj$ig0$1@news.netins.net>,
> "Mike Dobony" <sword@asarian-hostspamnot.net> wrote:
>
> > And also summing the channels. The more channels you use the lower each
> > individual channel gain has to be to end up with a 0 reading on the
mains.
> > I haven't had much sleep this weekend and have not been thinking clearly
so
> > maybe someone can give the correct LOG formula for finding the correct
> > setting for the individual channels based on the number of channels
used.
>
>
> Summing of incoherent signals- 3dB for every doubling of open channels
> Summing of phase coherent signals- 6dB for every doubling of open
> channels. chances are, that vast majority of your sources incoherent.
> And it is unlikely that any given time, that all channels will be at the
> same (relative) level to your mix buss.
>
> You don't need to calculate anything if you can PFL your submaster or
> mix buss. What you can do, is run your master fader at unity, and AFL
> the output. If you find that you are overdriving the mix buss, either
> attenuate channel faders, or back down your trims a hair.
>
> You don't need to make this a mental science project. Just watch how
> hard you drive the mix buss, and compensate if necessary.

"If one had a bank of oscillators set to 10 different frequencies set at
random and the outputs were all set at 1 volt each and added together, there
would be a time when the phases of each oscillator were the same and the
voltage would momentarily reach 10 volts and this means peaks much larger
than any individual signal. " Danley

Archived from groups: alt.audio.pro.live-sound,rec.audio.pro (More info?)

Geezer Sonics <geeze@deafguy.com> wrote in
news:geeze-ADA7DB.08065114082005@comcast.dca.giganews.com:

> In article <6Oqdna1Sr4BromPfRVn-2Q@comcast.com>,
> "Tim Padrick" <Padrick@comcast.net> wrote:
>
>> "Geezer Sonics" <geeze@deafguy.com> wrote in message
>> news:geeze-C709F9.08130203082005@comcast.dca.giganews.com...
>> >
>> > Summing of incoherent signals- 3dB for every doubling of
>> > open channels Summing of phase coherent signals- 6dB for
>> > every doubling of open channels. chances are, that vast
>> > majority of your sources incoherent. And it is unlikely
>> > that any given time, that all channels will be at the
>> > same (relative) level to your mix buss.
>> >
>>
>> "If one had a bank of oscillators set to 10 different
>> frequencies set at random and the outputs were all set at 1
>> volt each and added together, there would be a time when the
>> phases of each oscillator were the same and the voltage would
>> momentarily reach 10 volts and this means peaks much larger
>> than any individual signal. " Danley
>
> And if I had a million bucks in the bank, I'd call myself a
> millionaire. Neither event is likely to happen in real life.
> Danley's science experiment is not likely to happen during a
> live performance, hence it is not directly applicable to what
> most of the posters do every day.
>
Here, I'll start to disagree, because in music, notes and
harmonics from the different instruments do tend to behave
somewhat coherently, And there is often sufficient vibrato in
performances that one has to be careful of headroom. But,
clipping a half-cycle every few seconds is NOT going to be as
audible as clipping the total wavetrain from a gross overload.


--
Bob Quintal

PA is y I've altered my email address.