Tech: Input levels

Subject: Tech: Input levels
From: Herge
Date: 15 Sep 07 - 08:24 PM

Why is it I get such a range of input levels into our desk? If you take each PFL to balance before it reachs red on our desk - our mics and guitar line in allow for plenty of scope on the slider, but our fiddle input (either plugged staight in or slightly better with pre-amp) and radio mic have nearly maxium gain and full on the slider to compete. In total contast the line in from our ipod needs only min gain and min power on the slider and still nearly blows the roof off! Not very well articulated for those of a technical perspective but am trying to find out why some inputs have loads of power and others have very little

Subject: RE: Tech: Input levels
From: Joe Offer
Date: 15 Sep 07 - 10:22 PM

Refresh.
I'd like to get an answer on this one, too. I suppose somebody could come in and call us stupid and say inputs are different because they're different - but it's a real problem when you're trying to keep things in balance. How can I predict what input source is going to be at what level? How can I keep some sort of balance?
I have that problem with various inputs on my computer, and with various input sources on sound systems.
Herge, why don't you give a little more specific information about the problem you're having? I have to say I don't understand what you mean by "desk" and PFL. I'm guessing by "desk," you mean those big mixers that seem to be configured like the angled top of a school desk.
-Joe-

Subject: RE: Tech: Input levels
From: GUEST,QWTF
Date: 16 Sep 07 - 06:10 AM

Hiya,

Of course all inputs are different! But that doesn't make you stupid.

It sounds like it's impedance matching problems going on rather than actual level differences. It's a very complex subject, but in general the input impedance wants to be substantially higher than the thing that's being plugged into it. An normal Mike is 600 ohms, and wants to be plugged into something in the region of 10,000 ohms. An electric guitar will be several thousand ohms and will want to be plugged into several million.

An IPod is slightly different. It wants to drive a pair headphones, generally between eight and 400 ohms, but it's putting lots and lots of actual power into doing it.

One thing some people seem to do wrong is to assume that the connector type is the defining thing; if you cut the plug off and put a different on one it will all work fine. This isn't the case, an input needs to be matched. Most desks will have mike inputs shared with line inputs on each channel. The mike input will want to see something of about 600 ohms, and very low voltage (Millivolts) a line input will want to see something around 10,000 ohms and a voltage around 1 volt.

A DI box will match a line signal, or a guitar signal - around 10,000 ohms, but only millivolts - to a mike input. It's one of the most useful things you can have to bring levels slightly closer to each other.

It sounds like you're doing the right thing in setting up the mixer. Start by Pfl-ing each channel to get it to the right level, then bring the fader (sorry, not slider!) up to zero and everything should be pretty much balanced. If you find that you can't get the fiddle and radio mike up, then turn the gain on everything else down. Some people get terribly fretful about running a system at true unity gain, but it's really not that important!

Sorry about a slightly incoherent sunday morning essay. Hopefully someone else will sya it all much better!

Cheers,

QTWF

Subject: RE: Tech: Input levels
From: s&r
Date: 16 Sep 07 - 06:12 AM

The reason for the range of input levels can be poor design of the preamps from the pickups, poor pickups, wrongly fitted pickups, quiet instruments, quiet playing techniques etc. If your Ipod is so loud - are you going in to a line input or mic input - should be line. Is there an additional 20dB pad in the input channel as well as the trimpots?.

Pads to reduce the level can be obtained or made. Increasing the level needs a better pickup or preamp...

Needs more info to give better answer - get a good PA guy to check it out

Stu

Subject: RE: Tech: Input levels
From: Herge
Date: 16 Sep 07 - 08:01 AM

Hi
We use a band pickup through a fishman pre-amp and line input. We also use a Shure headset into a XLR input. Ipod into a line input. I dont know what a 20dB pad is or trimpots!

I think I'll hire a PA guy

Subject: RE: Tech: Input levels
From: s&r
Date: 16 Sep 07 - 08:21 AM

Looking at the specs for Ipods it seems that the only audio out is via headphone socket. If this is so, turn the volume down on the Ipod. Trimpots are just a name for the controls usually close to the input sockets used to balance the levels.

Never used the 'band for fiddle. The adverts claim that they plug directly into a desk - so does my Fishman bridge pickup, but it's better with a preamp. I suspect that position and tension could vary the fiddle output. The shure (radio?) headset should give plenty of sound, but there are a couple of things to watch - is the output level turned down on the receiver? Where is the mic positioned - should be close to the mouth but to one side to limit hf annd pops (they're equalised for this position)

Stu

Subject: RE: Tech: Input levels
From: GUEST,Ray
Date: 16 Sep 07 - 12:55 PM

Hi Herge - as you say the easiest way is to hire a PA guy to show oyu what to do - although its basically simple.

I don't know what type of desk you have but if its typical you will have an input socket - possibly a jack and an XLR - at the top or at the back of the desk for each chanel. For each chanel you will likely have a pad and a trim pot (also called chanel gain) - using a combination of these the idea is to even out the level of each thing you plug into the desk so that if two things are to come out of the speakers at the same level the position of the chanel faders should be roughly the same.

What you don't want is whatever you're plugging into the desk to overpower the chanel or, on the other hand be so low that you end up with elecrtical noise. The way to go is to monitor the chanel using PFL (with the chanel fader turned down) and gradually bring the chanel gain up until the meters give a good amount of green but not so much that they turn red. If you do this systematically for every input everything should end up at the same level.

You'll soon get to know when to use the pad - mics almost never & things with line outputs (e.g. keyboards) most of the time.
Ray

Subject: RE: Tech: Input levels
From: treewind
Date: 16 Sep 07 - 02:14 PM

Generally the input levels are different because of the physical characteristics of whatever's generating the input.

Dynamic mics, e.g. most stage mics like the SM58 and SM57 produce a small signal and need the input gain turning up relatively high.

Condenser mics have higher output. In short, the reason for this is that they have some simple amplification built in.

Electronic devices that run on batteries or AC tend to put out much higher levels (called "line level"). Ipods, CD players and electronic keyboards come into this category.

The input gain control, usually a small rotary knob right at the top of the mixer's channel strip near the connectors, and sometimes called "trim control" or "gain trim", is the proper place to adjust the inputs to compensate for these differences. As Ray says, there may also be a "pad" button which introduces a big step reduction in the gain, basically to give the input control more range, and a "line input" jack which similarly has fixed lower gain than the mic input (to the same channel)

Joe asked what's PFL - that stands for Pre Fade Listen and it's a push button for each channel. When you press it that channel's signal after the input gain stage but before the main fader is fed to the headphone socket and a meter. You use it to set the input level so the meters kick but don't go too high on each channel, all about the same amount, and then everything should be reasonably well matched and you only need to use the main faders for fine adjustments of balance and they should all be set in the top half of their travel.

That leaves a puzzle for me:
The radio mic has a powered receiver that should pout out a hefty signal. So should the fiddle mic when used with its preamp. I don't know why they should need full gain on the mixer. It looks like something may be wrong.

Anahata

Subject: RE: Tech: Input levels
From: Bernard
Date: 16 Sep 07 - 02:25 PM

You may find with the radio mic that the transmitter (belt pack or hand held) has its audio 'padded down' - it varies how this is done. Simpler VHF models usually have a gain control you tweak with a screwdriver, but UHF types are normally set up via the menu.

The input you use on the desk can make a big difference - if you go in on XLR ('Cannon' three pin) it is usually mic level, but a jack socket on the same channel would be line level, thus a lot less sensitive.

Subject: RE: Tech: Input levels
From: treewind
Date: 16 Sep 07 - 02:44 PM

Using the line jack could explain the low level from the fiddle pickup and the radio mic.

Herge: what mixer are you using?

Anahata

Subject: RE: Tech: Input levels
From: Herge
Date: 16 Sep 07 - 03:52 PM

We are using a Behringer XENYX 2222FX
Premium 22-Input 2/2-Bus Mixer with XENYX Mic Preamps, British EQs, 24-Bit Multi-FX Processor and USB/Audio Interface

Subject: RE: Tech: Input levels
From: GUEST,.gargoyle
Date: 16 Sep 07 - 11:28 PM

Keep this thread alive long enough - I may have some answere.

Agreed, VERY, EXTREAMLY!!!!! frustationing area.

Most requently our OUTPUT/INPUT (from stage) exceeds....we can tone down....we can manipulate.

HOWEVER, PLEASE in advance it would be very nice to know the tolerance levels and the OPTIMAL levels.....even with your own mix each venue is different....and if they give you 30 minutes pre it is a blessing..... and sometimes only UNION can be at the board!!!! (just let our man handle the mix)

CRAP!!!! At least let us know in advance what your system is..... and a picture of board would be nice.

Sincerely,
Gargoyle

it is one thing to sound like SH(*&%T because you are.....it is totally another because the venue is too big and you should have brought along a sound-man.

Subject: RE: Tech: Input levels
From: treewind
Date: 17 Sep 07 - 03:31 AM

OK - which input connectors are you using for the radio mic and fiddle?
If you're using the jack sockets for those, and the XLRs for all the other mics and instruments, you have 20dB less gain available on the jacks and that would account for the low levels on those two channels.

Your ipod is best connected to a stereo pair of line inputs e.g. 9-10 or 11-12 etc. and should not overload those. Set the button for -10; that's "consumer audio" live level, the +4 setting is for professional audio line level. Or you could use the CD/TAPE phono (RCA) but you won't have any EQ controls on it if you do that.

If you can set up using the PFL (called "solo" on that desk) buttons so the meter readings are about the same on each channel, they should sound about the same level in the mix. You should set the main faders to 0 (that's about 3/4 of the way up) use the master fader to set the approximate overall listening level, and then you should be able to get a decent balance by adjusting the main faders no more than +/- 10dB.

Anahata

Subject: RE: Tech: Input levels
From: treewind
Date: 17 Sep 07 - 03:34 AM

P.S. if the problem is the use of the jack sockets, just rip off the jack plugs and solder on some male XLRs instead!

Hot to pin 2, ground/shield to pins 1 and 3. Make sure phantom power is turned off on the mixer!

Anahata

Subject: RE: Tech: Input levels
From: s&r
Date: 17 Sep 07 - 04:05 AM

Or better still use a DI

Stu

Subject: RE: Tech: Input levels
From: Bernard
Date: 17 Sep 07 - 07:20 AM

The main purpose of a DI is to balance the signal so you can send it to a mic input over a distance of more than around six feet without inducing hum or other interference.

However, it is also very useful (as Stu just said) for impedance matching, as most have a 0dB, 20dB and 40dB pad switch, plus an earth lift switch.

Please note that some guitar transducers don't like transformer balanced ('passive') DI boxes, and prefer a good quality electronic version. Passive boxes can make them sound thin and nasty, with reduced level.

Using a DI also removes the problem of shorting the Phantom Power when putting an unbalanced line into an XLR input on a desk where Phantom is global (as opposed to switchable on each individual channel).

Subject: RE: Tech: Input levels
From: Andy Jackson
Date: 17 Sep 07 - 11:38 AM

The trouble is that the answer is in the thread title...its a very "TECH" business.
Although I can see an element of truth in some of the answers above, te real answer is a bit of homework. There are plenty of books available at very reasonable prices which will give you an insight into the problems.
Avoid generalisations relating to the connectors, for they are only convenient joins in the wire. It is what level of signal that is coming down the wire compared to what the input "expects" to see that matters.
A simple book will shed the light on the small print on all the bits you are connectg together and help you match levels.
Good luck, you have passed the first hurdle of realising something is wrong and wanting to know why.

Andy

Subject: RE: Tech: Input levels
From: Herge
Date: 17 Sep 07 - 01:26 PM

I do use the phantom power for a AKG 1000S mic (I could turn it off and use the battery) - do you think this would help?


All inpits as follows
1 x SM87 (banjo)- XLR - XLR (no problems)
1 x shure VHF radio headset XLR - XLR (low volume even with gain up on reciever and desk)
1 x band fiddle pick-up - jack to jack (low volume even through fishman pre-amp)
1 x AKG 1000s mic (accordion)XLR - XLR (no problems)
2 x line in for guitars jack to jack (no problems)
1 x SM58 vocal mic - XLR - XLR (no problems)
1 x Ipod from head phone out to XLR (loads of volume)

Subject: RE: Tech: Input levels
From: s&r
Date: 17 Sep 07 - 01:34 PM

Turn volume down on Ipod.
Make sure headset is against corner of mouth, and talk/sing louder (G)
Try other pickups on fiddle if poss and see if the problem is acousti - ie quiet fiddle or player.

Stu

Subject: RE: Tech: Input levels
From: treewind
Date: 17 Sep 07 - 02:57 PM

The Ipod is stereo. You need to connect that to two inputs (that's definitely not pins 2 and 3 of the same XLR, it will give you a mono signal consisting of the differentce betwen L and R from the ipod - very weird)

Do what I suggested and use two jacks into a stereo channels on the mixer.
The wiring goes like this:
* headphone tip - left jack tip
* headphone ring - right jack tip
* headphone ground - both jacks ground

You can buy a ready-made cable to do that from a good audio shop.

I'd use the phantom power for the C1000 and get a DI for the fiddle.
Batteries are just one more thing to worry about.

Anahata

Subject: RE: Tech: Input levels
From: Herge
Date: 17 Sep 07 - 05:38 PM

Any make or model for the DI?

Subject: RE: Tech: Input levels
From: s&r
Date: 17 Sep 07 - 05:53 PM

Something like this

Subject: RE: Tech: Input levels
From: s&r
Date: 17 Sep 07 - 05:58 PM

The shure could be the same as we used to use for our caller - it was directional and she often had it twisted so the mic was facing outwards. Not obvious because of the windshield

Stu

Subject: RE: Tech: Input levels
From: Herge
Date: 18 Sep 07 - 03:59 AM

Should I connect the DI box to the sesk by a jack lead or XLR?

Subject: RE: Tech: Input levels
From: treewind
Date: 18 Sep 07 - 04:07 AM

XLR
(otherwise you'll have the same problem all over again, the whole point was to get into the desk's XLR input to get 20dB more gain...)

Anahata

Subject: RE: Tech: Input levels
From: GUEST,.gargoyle
Date: 19 Sep 07 - 01:37 AM

Scrap the IPEE crap.

Is there a meter, if we adjust to 1/3 or midtone range that can tell us precisely, what each mic/instruments output is? (They all seem different)

Let us just say.....coming OUT of the MIXING board we want EVERTHING equal....(They are not because there were not equal going in).....the mixers change with every venue.

It is enough to scream - go punk - and then return to all acoustic with a omni single mic.

Sincerely,
Gargoyle

Subject: RE: Tech: Input levels
From: treewind
Date: 19 Sep 07 - 03:34 AM

BTW Behringer Ultra-DI's cheaper HERE

Anahata

Subject: RE: Tech: Input levels
From: Grab
Date: 19 Sep 07 - 08:35 AM

IIRC when I went shopping last year, it was £20 for a 2-way DI or £50 for the Behringer 8-way job, so I got the 8-way for our band (potentially 4 guitars, keys and violin feeding it). But that's a rack-mount job so really needs a flight case, where the little 2-way DIs are small and tough and can just be chucked in a gig-bag.

Re balancing levels Herge, if you can find a soundman to do the job then you'll sound better out front.

Graham.

Subject: RE: Tech: Input levels
From: Herge
Date: 19 Sep 07 - 11:05 AM

Got the DI today so will try it at a gig tonight - will let you know how it goes

Herge

Subject: RE: Tech: Input levels
From: Bernard
Date: 19 Sep 07 - 12:24 PM

I still think your radio mic problem is the TRANSMITTER gain - there is a trim control in the belt pack that needs tweaking with a small plastic screwdriver (usually supplied with the system).

Subject: RE: Tech: Input levels
From: GUEST,Qtwf
Date: 19 Sep 07 - 12:56 PM

It's not a bad idea Graham!

Where are you Herge? Does anybody out there want to volunteer an evening at a gig to help out??

Cheers,

QTWF

Subject: RE: Tech: Input levels
From: s&r
Date: 20 Sep 07 - 03:24 AM

How did it go?

Stu

Subject: RE: Tech: Input levels
From: Herge
Date: 20 Sep 07 - 12:32 PM

Hi Folks - well


Got the DI - read the instructions - wired up the DI to mixer - plugged in fiddle - turned on - played music - no sound - turned up on fader - some sound and loud humming - fiddled with a selection if the buttons on DI - no difference - unplugged DI - plugged fiddle in direct - fiddled with gain and fader until reasonable sound obtained, taking on board suggestions above lowering gain on other inputs - played gig - went well - went home - need sound person - anyone in Northern Ireland can help - ordered new radio mic mic.

Subject: RE: Tech: Input levels
From: treewind
Date: 20 Sep 07 - 02:19 PM

I presume the DI had either a working battery or phantom power switched on?

Anahata

Subject: RE: Tech: Input levels
From: Herge
Date: 20 Sep 07 - 02:25 PM

Had a working battery in it, but I ran it off phantom

Subject: RE: Tech: Input levels
From: fiddler
Date: 21 Sep 07 - 04:30 AM

Great thread, I mix from the satge quite often - not ideal - a big headache when you are playing as well.

I'd like to get a good sound man - or woman - very rare.

Andy

Subject: RE: Tech: Input levels
From: Herge
Date: 21 Sep 07 - 06:39 PM

Ran out of ideas?

Subject: RE: Tech: Input levels
From: Herge
Date: 23 Sep 07 - 04:59 AM

Got a new headset - sennheiser EW152 - difference is amazing must have been a problem with our shure set - (it had been gigged for 7 years) - much happier with overall sound.

Thanks for the advice

Herge

Subject: RE: Tech: Input levels
From: Grab
Date: 23 Sep 07 - 04:11 PM

Andy, check your local musicians website. There's a good one for my area called CambridgeBands.com - see if your local music shop knows of something similar for your area.

Graham.

Subject: RE: Tech: Input levels
From: s&r
Date: 24 Sep 07 - 03:16 AM

Did you get the fiddle sorted Herge?

Stu

Subject: RE: Tech: Input levels
From: s&r
Date: 26 Sep 07 - 01:53 PM

refresh