You are here

Push the levels - desk or PA?

For performing musicians and engineers: stagecraft, engineering and gear.

Re: Push the levels - desk or PA?

Postby Hugh Robjohns » Wed Jan 30, 2019 12:09 pm

Dave B wrote:So if I read this right, the power amp runs at full power at all times, and the knob is merely controlling how much is being fed in?

This is the normal case. Power amps generally have a fixed voltage gain -- typically 25-30dB. Any required level adjustment is normally courtesy of an input attenuator.

Small signal amplifiers (eg, mic preamps) usually (but not always!) do have adjustable gain, but most other gain stages are typically fixed gain and are either preceded or followed by adjustable attenuators (eg, faders).

H
User avatar
Hugh Robjohns
Moderator
Posts: 26386
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Push the levels - desk or PA?

Postby Wonks » Wed Jan 30, 2019 12:15 pm

I was just trying to point out that +24dBu for the line and +20dBu for the mic input which is then increased by 30 dB or more in the pre-amp in mic mode, to say +50dBu just doesn't make any sense. Therefore those figures logically can't be for maximum signal output.

Nuff said. Dave can check it out at his next rehearsal, tomorrow night. Take a pillow to cover the speaker, Dave!
User avatar
Wonks
Jedi Poster
Posts: 10739
Joined: Thu May 29, 2003 12:00 am
Location: Reading, UK
Correcting mistakes on the internet since 1853

Re: Push the levels - desk or PA?

Postby Sam Spoons » Wed Jan 30, 2019 12:16 pm

I have DXR10s and when I asked the tech dept what the power amp specs really meant they were unable or unwilling to tell me, It seems that (semi-) pro PA manufacturers have become infected with the same disease as 'In Car Entertainment' makers. Yamaha quote 'continuous' and 'dynamic' for the power amp outputs.

I do realise the important figure is the max SPL but, being a little "Old School" and, I guess, a bit of an anorak, I like to know these things. I also know that the concept of 'RMS Watts' is itself flawed but it is, at least I believe it is, consistent.
User avatar
Sam Spoons
Jedi Poster
Posts: 11620
Joined: Thu Jan 23, 2003 1:00 am
Location: Manchester UK
Finally taking this recording lark seriously (and recording my Gypsy Jazz CD)........

Re: Push the levels - desk or PA?

Postby Wonks » Wed Jan 30, 2019 12:23 pm

The problem with rating larger class D power amps is that their music (and obviously peak) power rating can be much larger than the available electrical power supply, so whilst their practical music power rating can be a lot higher, their RMS rating remains limited as they can only produce a large RMS value for a few milliseconds before all the stored energy in the capacitors is drained and the voltage levels plummet.
User avatar
Wonks
Jedi Poster
Posts: 10739
Joined: Thu May 29, 2003 12:00 am
Location: Reading, UK
Correcting mistakes on the internet since 1853

Re: Push the levels - desk or PA?

Postby manleyelop » Mon Feb 11, 2019 10:56 pm

This op's question really interests me also i usually have my power amps on full each of these are through a dbx crossover would it be best to have my desk fader levels more around unity & back off the power amp level?
i usually find my faders are below unity but still get good sound results but would rather do things different if what im doing is bad practice
User avatar
manleyelop
Regular
Posts: 290
Joined: Tue Aug 24, 2010 12:00 am
Location:

Re: Push the levels - desk or PA?

Postby AlecSp » Mon Feb 11, 2019 11:24 pm

Blimey, the OP does seem to have complicated things with all the crunching of (unreliable?) numbers.

My approach is much more hands on. Ensure no clipping in the channel strips/mixer signal path. Run your typical noise at 0dB on the desk i.e., fader positions - I don't care about what the numbers on the meters say, as long as they're allowing for plenty of headroom (digital mixer here). Then adjust the speakers for the required level for the show. That way, you can mix at 0 as standard, but have another 10dB of master gain if you need it.

Whatever happens, you shouldn't be damaging the speakers by asking too much from them - that's the benefit of the system protection. Doesn't mean they won't sound ropey as you push them past the limiter. But carry on hands on - look and see if the limiter light on the speaker is on more than occaisionally at both "standard" and "more pokey" levels. Do this a few times and you should soon be familiar with what your kit can do.

In the end, gain is gain, whether it's in the channel pre, the channel fader, the DCA, the master fader, or the speaker input (although the latter is more about attenuation, but that's no more than negative gain).

Using your ears can be way more effective than using a calculator... :thumbup:
AlecSp
Regular
Posts: 434
Joined: Tue Nov 16, 2004 1:00 am

Re: Push the levels - desk or PA?

Postby Folderol » Mon Feb 11, 2019 11:28 pm

Late to the party here.
I've always considered this to be conflicting requirements.
In the most extreme cases, for the best noise performance you want the last control in the line to be doing most of the attenuation, but for the best distortion performance it should be the first (bear with me I'm an old valve jockey).
However, over time input stages have become quieter and with better linearity. These days, even on my modest setup I tend to start out with everything in their mid ranges and adjust final volume at the amplifier for convenience more than anything else.

As for what peak power means to the listener. It is meaningless without the centre frequency, bandwidth and duration. The surprising one is duration. Try playing with various simple waveforms at different frequencies and an envelope shaper and you will find the fewer the cycles the quieter it sounds. What's even more strange is that (especially at higher frequencies) if you increase the drive you find a point where it becomes very uncomfortable without sounding loud - and I'm not talking about when you're going out of your normal hearing range.

P.S. I forgot the magic words.
"In my opinion/experience"
User avatar
Folderol
Jedi Poster
Posts: 10115
Joined: Sat Nov 15, 2008 1:00 am
Location: The Mudway Towns, UK
Yes. I am that Linux nut.
Onwards and... err... sideways!

Re: Push the levels - desk or PA?

Postby witzendoz » Tue Feb 12, 2019 12:40 am

I have a touchmix 16 and the touchmix does seem to have less output than some other mixers.

What I have found is that even if you push each channel quite hard with the manual knob the main left / right outs still seem a little low output at fader unity. However if you go into the individual channel settings there is a digital gain control. This gain is after the channel manual knob so that a gain increase here does not overdrive the channel (as long as you don't go mad I suppose). So gain each channel up a few dB and then when setting the manual gains on each channel to a sensible level the master left / right will increase without clipping the channel gain.

Hope that made sense.
User avatar
witzendoz
New here
Posts: 6
Joined: Tue Apr 09, 2013 12:00 am
Location: Fremantle Australia

Re: Push the levels - desk or PA?

Postby Hugh Robjohns » Tue Feb 12, 2019 10:43 am

manleyelop wrote:...would it be best to have my desk fader levels more around unity & back off the power amp level? i usually find my faders are below unity but still get good sound results but would rather do things different if what im doing is bad practice

It depends how much below unity they are!

You want to keep your channel faders around unity to maximise the precision and ease of your balancing adjustments. If you end up running the main output fader at -10dB to achieve a sensible level in the room, that's no big deal but if they're at -30 the gain structure is going a bit awry.

It's all about optimising the signal-to-noise ratio while also maintaining a sensible headroom margin.

In your case, you also have the option of optimising levels between the mixer and amps with the DBX crossover, of course...
User avatar
Hugh Robjohns
Moderator
Posts: 26386
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Push the levels - desk or PA?

Postby manleyelop » Tue Feb 12, 2019 11:34 am

Hugh Robjohns wrote:You want to keep your channel faders around unity to maximise the precision and ease of your balancing adjustments. If you end up running the main output fader at -10dB to achieve a sensible level in the room, that's no big deal but if they're at -30 the gain structure is going a bit awry.

It's all about optimising the signal-to-noise ratio while also maintaining a sensible headroom margin.

In your case, you also have the option of optimising levels between the mixer and amps with the DBX crossover, of course...

Yes i must admit some of my channel faders where floating around fairly low but not -30 should i adjust those faders to around -10 check gain levels & lower the power amp volume ?
Although my desk master fader was in good health floating around unity

Thing is i do pfl each channel when setting up im using an old allen & heath mix wizard
User avatar
manleyelop
Regular
Posts: 290
Joined: Tue Aug 24, 2010 12:00 am
Location:

Re: Push the levels - desk or PA?

Postby Hugh Robjohns » Tue Feb 12, 2019 11:53 am

I wouldn't worry too much if the masters are -20dB or so, especially at the start of the gig (it's not unusual for the master to creep up a bit as the gig progresses). A decent desk should still be quiet enough that your signal-noise ratio isn't too badly compromised running in that way -- at least in a live sound situation.

But if it's a regular thing and concerning you, then dial the power amp input attenuators back by 10 or 20dB and run the console masters closer to unity.

H
User avatar
Hugh Robjohns
Moderator
Posts: 26386
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Push the levels - desk or PA?

Postby manleyelop » Tue Feb 12, 2019 1:25 pm

Hugh Robjohns wrote:I wouldn't worry too much if the masters are -20dB or so, especially at the start of the gig (it's not unusual for the master to creep up a bit as the gig progresses). A decent desk should still be quiet enough that your signal-noise ratio isn't too badly compromised running in that way -- at least in a live sound situation.

But if it's a regular thing and concerning you, then dial the power amp input attenuators back by 10 or 20dB and run the console masters closer to unity.

H
Thanks Hugh My desk master fader usually sits around unity during live gigs from memory,ive read about folk liking to see there ch faders sit around unity also but some of mine are way down from that but that is where the mix sounded good to me perhaps im just worrying about a problem that doesn't exist :headbang:
User avatar
manleyelop
Regular
Posts: 290
Joined: Tue Aug 24, 2010 12:00 am
Location:

Re: Push the levels - desk or PA?

Postby Hugh Robjohns » Tue Feb 12, 2019 2:14 pm

manleyelop wrote:ive read about folk liking to see there ch faders sit around unity also but some of mine are way down from that but that is where the mix sounded good to me perhaps im just worrying about a problem that doesn't exist :headbang:

The faders have a non-linear scale, so the finest resolution (level change per mm of travel) is around the unity mark. That's why it's a good idea to arrange channel input levels so that you can keep the faders near unity during the mix/show.

If you find you're having to work with a channel fader well below that, it's simply because you don't need much of that source's contribution in your mix (perhaps you're hearing a lot of it acoustically from the backline, or it's a banjo that you don't want audible in the mix... ;-) ).

You could simply turn down the channel's input gain control to allow you to raise the fader closer to unity while still contributing very little to the mix -- but bear in mind that will also reduce the level being fed out to any pre/post fade aux send and any direct output recording feeds.

H
User avatar
Hugh Robjohns
Moderator
Posts: 26386
Joined: Fri Jul 25, 2003 12:00 am
Location: Worcestershire, UK
Technical Editor, Sound On Sound

Re: Push the levels - desk or PA?

Postby manleyelop » Tue Feb 12, 2019 3:35 pm

Hugh Robjohns wrote:The faders have a non-linear scale, so the finest resolution (level change per mm of travel) is around the unity mark. That's why it's a good idea to arrange channel input levels so that you can keep the faders near unity during the mix/show.

You could simply turn down the channel's input gain control to allow you to raise the fader closer to unity while still contributing very little to the mix -- but bear in mind that will also reduce the level being fed out to any pre/post fade aux send and any direct output recording feeds.

H

yes that's what i was wondering about some of my ch faders have been hovering around -20 mainly drums & bass & im wondering if that's a bad way of doing things.the trim gain pot on the kick drum was pretty low so perhaps i should have padded it down & raised the trim level so i could raise the ch fader more
User avatar
manleyelop
Regular
Posts: 290
Joined: Tue Aug 24, 2010 12:00 am
Location:

Re: Push the levels - desk or PA?

Postby AlecSp » Tue Feb 12, 2019 3:51 pm

manleyelop wrote:ive read about folk liking to see there ch faders sit around unity also but some of mine are way down from that but that is where the mix sounded good to me perhaps im just worrying about a problem that doesn't exist :headbang:
If it sounds good to you (and others) then don't sweat over it. Better working practices can make you life easier, but your ears shouldn't be lying!
AlecSp
Regular
Posts: 434
Joined: Tue Nov 16, 2004 1:00 am

PreviousNext