g_randybrown
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OT: Sensitivity vs gain, trim, pre-amp etc
We play at a church every Sunday where I send a sub-mix from our board to the house board. The "sound man" for the church tells me he's not getting a strong enough signal from me (although my VUs are showing I'm sending a strong signal). I look at the house board and he's got the channels for my sends set with the volume sliders way down (like -20 or so) and the "sensitivity" (top pot on each channel where you would ordinarilly find gain or trim) cranked. Me assuming "sensitivity" is the same as gain I tried to explain to him that one ordinarily sets the sliders around zero and then adjusts the gain (if necessary) and then fine tune with the slider but he says "no, that's not the way it works!!!". I've been letting this slide because the guy has been running sound for this church for a long time but now he wants to get together tomorrow to "discuss our responsibilities". I have already been given the authority by the minister to "do whatever is necessary" but I'd like to hear it from you guys that the guy is wrong here.....I've been wrong before  Thanks very much Randy
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papa2004
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 13:42:02
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I have already been given the authority by the minister to "do whatever is necessary" but I'd like to hear it from you guys that the guy is wrong here.....I've been wrong before You're probably right (presuming the board you're sending the "sub-mix" through is properly calibrated and that the "sensitivity" pot on the house board is actually a trim/gain control for the preamps)...I seem to recall working on a console about 25 or so years ago that had a "sensitivity" pot which was, in fact, the preamp trim pot. My advice, call in an outsider. Sounds like the church sound guy is pretty much set in his ways and might have some anger management/control issues. It would probably be in your best interest not to alienate him since you have to work with him on a weekly basis. 
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 14:52:19
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My advice, call in an outsider. Sounds like the church sound guy is pretty much set in his ways and might have some anger management/control issues. It would probably be in your best interest not to alienate him since you have to work with him on a weekly basis. Thanks Papa, I don't know an outsider so I think I'll meet with the guy at the church and try to talk it out...wish me luck. Thanks again, Randy
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jcatena
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 16:04:16
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> although my VUs are showing I'm sending a strong signal
I suppose this means line levels, for example around +4dBu? In this case the main board would need to have the input gain (or sensitivity, it's the same) all the way down, or nearly with an attenuation pad engaged. Some mixers without pads may even saturate with the minimun gain and an higher than +4dBu input signal.
If the main mixer had the input gain crancked up, something is wrong. Check the conection from your output to the mixer's input. If it is fully balanced, or unbal to bal, etc, make sure all three pins are correctly connected as required.
The guy at the church is right if I understood well. The channel fader does not matter when adjusting the input gain. He should be looking at PFL level to adjust gain, and PFL by definition (Pre-Fader Listen) is independent of fader. If he had to crack up the input gain very much, he's indeed receiveing a very weak signal.
Jose Catena DIGIWAVES, S.L.
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 16:30:32
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I suppose this means line levels, for example around +4dBu? In this case the main board would need to have the input gain (or sensitivity, it's the same) all the way down, or nearly with an attenuation pad engaged. Some mixers without pads may even saturate with the minimun gain and an higher than +4dBu input signal.
As I recall this board doesn't have a pad but we haven't needed one
If the main mixer had the input gain crancked up, something is wrong. Check the conection from your output to the mixer's input. If it is fully balanced, or unbal to bal, etc, make sure all three pins are correctly connected as required.
I'm coming out unbalanced 1/4 inch stereo to a direct box. On the direct box there is a -40 and -20 db but I have it set to zero.
The guy at the church is right if I understood well. The channel fader does not matter when adjusting the input gain. He should be looking at PFL level to adjust gain, and PFL by definition (Pre-Fader Listen) is independent of fader. If he had to crack up the input gain very much, he's indeed receiveing a very weak signal.
With the gain all the way down and the fader set at zero it gets good enough signal that I didn't need to add any gain even if I went slightly above zero but still in that optimum range...my point is he had the gain cranked and the fader way down to like -20 or -30 (and if I recall the master fader down some too). I can't think of any situation that would be a correct setting (faders down gain cranked)...would you agree with that?
Thanks very much,
Randy
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 16:39:14
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The person may have the sensitivity/trim/gain what have you set up that way to accommodate a monitor, effect, tape, or broadcast sends.... The sound may not just go in straight line :-) I suggest a nice open minded discussion. :-) best, mike edit spelling
post edited by mike_mccue - 2009/07/07 16:51:38
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jcatena
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 16:40:23
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> With the gain all the way down and the fader set at zero it gets good enough signal The fader does not matter here. If he gets good PFL reading (for example 0 dB) with the input gain at minimum or near the minimum, everything is OK. The right way to adjust the input gain is to use the PFL as meter and set the input gain so that PFL reads about 0 dB, or highest possible while ensuring it does not clip. This ensures proper gain staging and best SNR. Then the channels, group or master faders depend on mix and output requirements. May perfectly be -20 -30 or whatever does it. If you set the faders at unity gain and lower input gain, as you suggest, you are only adding noise. Well, unnecessarily reducing headroom too.
post edited by jcatena - 2009/07/07 17:06:58
Jose Catena DIGIWAVES, S.L.
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 17:30:47
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ORIGINAL: jcatena
> With the gain all the way down and the fader set at zero it gets good enough signal
The fader does not matter here. If he gets good PFL reading (for example 0 dB) with the input gain at minimum or near the minimum, everything is OK.
The right way to adjust the input gain is to use the PFL as meter and set the input gain so that PFL reads about 0 dB, or highest possible while ensuring it does not clip. This ensures proper gain staging and best SNR.
Then the channels, group or master faders depend on mix and output requirements. May perfectly be -20 -30 or whatever does it.
If you set the faders at unity gain and lower input gain, as you suggest, you are only adding noise. Well, unnecessarily reducing headroom too.
My, how quickly things change around here...so maybe I'm full of crap!!!! So perhaps I was taught wrong (many,many moons ago) ....I was taught (in general) that you bring the fader up and around unity and then if (and only if) you need more signal then boost that signal with gain/pre-amp!!! This could be embarrasing as hell at our meeting on Thursday....but damnit I feel sure if you heard my mix you'd agree it sounds much better....OMG what if we're both full of crap!!! I'm over at the Rane site now but I won't have time to truly get into this until tomorrow. I hate your stupid posts....they suck!!!!  but hey....thanks very much for setting me straight!!! I mean I'd rather tell the guy I'm full of crap than tell him he's full of crap and the find out...well you know
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John
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 18:03:27
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What mixer boards are we talking about? I can read up on them and see if one or the other needs special treatment. My first view is you have it right set the fader to unity and adjust the trim. From there make further adjustments with the fader. I don't see any need to complicate this.
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jimmyman
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 18:24:38
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i cant say whats right or wrong. but i think in terms of
reference points. set all the faders to 0. even the master
(if posible) turn the power amps all the way down and
also the trims.
take an instrument or vocal and get say about a minus
20 db level on the main mixers meters using the trim.
bring up the power amps levels to the desired level.
then do the same process for the other instruments
(leaving the power amps set)
at this point whether the stage is getting good
moniter levels or whatever is not yet adressed.
( this is a working with each other process)
between the sound man and the players.
once the main mix is well balanced then its time to
see if the the "band" is happy with things. by the way
if there is a stage mixer much of the same setup techniques
apply.
if the stage mixer is "independant" of the mains
for monitering then things are all the better. if not then
some "working together" is needed.
the object is to try and not even rely on "faders"
to correct but to tweek. what happens is sometimes
a soundman feels that if the "boards" levels on
each channel isnt all "curvey" then somethings wrong.
its all about learining and being willing to. sitting behind
a mixer dont make a person a soundman.
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jcatena
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 18:31:50
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> My first view is you have it right set the fader to unity and adjust the trim Sorry, John, that is not the way to do it. Each stage gain amplifies everything and adds noise, including upstream stages noise. That's why we want the gain to be largest at the front end, the pre-amplifier. We want the signal to be around 0dB at the preamplifier output. All circuitry downstream is designed to work at that level, while the preamps are designed for lowest noise because it may receive much smaller signals. If you work with lower levels at the preamp output, overall SNR is degraded in the same amount. I.e. if we set the input gain to obtain -20dB, for example, we may lose up to 20 dB of SNR at the output. This is best adjusted using the PFL as meter, and normally the channel is muted or at low level while adjusting input gain. If we set the faders at unity gain and then set the input gain, two things may happen: - If you set the input gain so that output is 0 dB, the adjustment is equivalent to the PFL way, only that you will be sending a 0 dB output to the PA, and I think you don't want to do that without need. - If you set the input gain to have "enough" level by ear, whatever it means, you lose SNR as much as the level is below 0 dB, and you lose the ability to raise level later up to higher levels. Take my word on this, I designed pro consoles 26 years ago, and did a lot of demoing and live mixing, I know how they work and how to get the most of their performance. A cousin of me is studying sound engineering and I verified his books tell the same (otherwise the books would be wrong, not me ggggg).
post edited by jcatena - 2009/07/07 18:47:41
Jose Catena DIGIWAVES, S.L.
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kgarello
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/07 19:01:22
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The Mackie Manual for the CR1604 explicitely states to set the fader levels at Unity before setting the trim (I don't think the meter mechanism was prefader). I don't think you can blanketly say either is correct without reading the manual.
I know that my Behringer (as well as my onyx) has a prefader meter.
It doesn't sound right to have the input trim cranked on a line level signal if it is a mic channel. Some boards have a line in button.
Definately review the manual before the meeting.
Ken
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Bristol_Jonesey
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 06:06:02
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All of my Soundcraft manuals say you should set your gain from the channel trim pot FIRST, by using the PFL bus.
Your main faders are used purely for mixing.
Suppose you've got a signal on tape (tape?) that needs to be brought into your song at a very low level.
If you set your fader at unity and reduce the input gain, your fader is amplifying a higher proportion of noise, simply because the gain is set too low (the lower the signal, the lower the S/N ratio is)
But if you set the input gain to read 0db or thereabouts on the PFL, attenuating the signal to the desired level via the fader cannot introduce noise at any point.
Simples.
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 09:07:46
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On these occasions I like explain that we were all taught wrong:
"set the fader levels at Unity before setting the trim"
Is like some mindless mantra many of us (including myself) were specifically taught.
I've been breaking that *rule* for about 25 years now. :-)
At a recent gig I was cornered by one of the bands techs... whom inquired as to why I was not running the trim/fader relationship by the "book". (faders at unity) It didn't stop until the musicians pulled him off and explained I'd been doing this job for a while. :-)
What a pain to have to explain that sort of stuff while you're trying to ring out a system.
best regards,
mike
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cebg
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 09:43:36
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Sounds like a couple of issues:
1) sound trouble
2) people trouble
I can't give advice on sound trouble...other than, can you test the way you think it should be setup before you meet and then talk to him about the results afterward? Chat about cost/benefit of doing it both ways with him.
If you are the one running the show, I'd say you have the authority to make the decision. However, if it really doesn't matter which way the settings go to get the same results, I'd say let him have his way if it means avoiding a potential blowup...
In this world you will have trouble. But take heart! I have overcome the world. -Jesus Christ
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Beagle
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 10:34:49
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regardless of whether you get better SNR using the trim or the fader first - the initial problem is that the soundman says that randy is not sending him a hot enough signal, however, according to randy, the trim is cranked up and the fader is down and the soundman doesn't want to turn the fader up.
there are two solutions:
crank the output of the mixer from the stage until it starts to distort, then back off - that will be sending him the hottest signal you can.
get him to move the fader. if the signal isn't loud enough in the mix - then turn it up. I don't understand the problem there.
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 11:10:07
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On these occasions I like explain that we were all taught wrong:
"set the fader levels at Unity before setting the trim"
Is like some mindless mantra many of us (including myself) were specifically taught.
I was actually taught this in a college music technology class....a long time ago but still...
What a pain to have to explain that sort of stuff while you're trying to ring out a system.
Yikes, I remember the guy saying "that's not the way it works" and "we just have different ways of doing things" when I was complaining about the sliders being down...I was so sure he didn't know what he was doing (until reading Bristol's and Mikes posts)...I'll have to apologize and ask him to forgive me now.
This has been an enlightening thread to say the least....uncomfortable as hell but enlightening.
Time for a big huge plate of crow I guess...damn...live and learn I guess.
Thanks very much to everyone,
Randy
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 11:17:33
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ORIGINAL: Beagle
regardless of whether you get better SNR using the trim or the fader first - the initial problem is that the soundman says that randy is not sending him a hot enough signal, however, according to randy, the trim is cranked up and the fader is down and the soundman doesn't want to turn the fader up.
there are two solutions:
crank the output of the mixer from the stage until it starts to distort, then back off - that will be sending him the hottest signal you can.
get him to move the fader. if the signal isn't loud enough in the mix - then turn it up. I don't understand the problem there.
Thanks Beag, we're going to meet to try to determine the solution.
G. Randy Brown Windows 10, 64 bit, PlatinumIntel Core i7-3770S Asus P8Z77-V LK mobo 4X8GB Corsair XMS3 memory 500 GB Crucial BX100 SSD (OS)two WD Black 1 TB HDDSAPPHIRE DUAL-X 100314-4L Radeon HD 6970 2GB 256-Bit GDDR5 Presonus AudioBox 22VSLyoutube.com/crystalclearnm
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Bristol_Jonesey
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 11:48:10
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The other thing is, where are you taking the feeds to send him? On my board, there's many possibilities - channel direct outs, tape sends, group outs, aux sends, you could also 'sniff' the insert points. Just to add to the happy confusion 
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 11:57:41
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ORIGINAL: Bristol_Jonesey
The other thing is, where are you taking the feeds to send him?
On my board, there's many possibilities - channel direct outs, tape sends, group outs, aux sends, you could also 'sniff' the insert points.
Just to add to the happy confusion
I'm coming out this board "control room" stereo, unbalanced to a 2 channel direct box. I noticed the feed on his end is coming in XLR on 2 channel strips but that's all I know. Any advice will be very much appreciated, Randy
G. Randy Brown Windows 10, 64 bit, PlatinumIntel Core i7-3770S Asus P8Z77-V LK mobo 4X8GB Corsair XMS3 memory 500 GB Crucial BX100 SSD (OS)two WD Black 1 TB HDDSAPPHIRE DUAL-X 100314-4L Radeon HD 6970 2GB 256-Bit GDDR5 Presonus AudioBox 22VSLyoutube.com/crystalclearnm
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 12:12:43
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ORIGINAL: Beagle
regardless of whether you get better SNR using the trim or the fader first - the initial problem is that the soundman says that randy is not sending him a hot enough signal, however, according to randy, the trim is cranked up and the fader is down and the soundman doesn't want to turn the fader up.
there are two solutions:
crank the output of the mixer from the stage until it starts to distort, then back off - that will be sending him the hottest signal you can.
get him to move the fader. if the signal isn't loud enough in the mix - then turn it up. I don't understand the problem there.
It's hard to say what he is thinking... perhaps the trim is cranked BECAUSE it seems the input is too low... I mean that part seems obvious.... perhaps he feels that when you jam the gain at the trim the character of the sound suffers and he would rather have a hot signal arrive so he can use less gain at that stage? Those are possibilities... and once again there is the issue of sends to other places etc. The point is... he thinks he needs some change... I suggest one assume he wants to be helpful and make good sound as much as the musicians... so I recommend that the discussion stay relaxed and open. Maybe give him what he's asking for... at least so he can try it, experiment, what ever... don't look at your meters... just send him what he's asking for... and see if he doesn't ask to return to where you are at now. Try to find out if he is trying to solve a tonal, routing, or mix issue? He may not know yet and just know that he has a lack of control. I haven't paid enough attention is this about an instrument or a sub mix send? best regards, mike
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 12:30:50
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I haven't paid enough attention is this about an instrument or a sub mix send? It's a sub-mix...I basically have a PA setup on stage and sending him that signal for the house system.... if you'd be so kind as to read the post just above yours, you'll see how I'm sending. Thanks Mike, Randy
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 13:51:03
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"I'm coming out this board "control room" stereo, unbalanced to a 2 channel direct box. I noticed the feed on his end is coming in XLR on 2 channel strips but that's all I know.
Any advice will be very much appreciated,
Randy" Ok, so you're coming out with what appears to be a unbalanced output that has a Max output of 22dBU (that's on a good day and probably not looking to closely at the distortion specs) and your hitting a direct box (that, to focus on one simplistic aspect, is essentially reducing your moderate line level signal into "mic" level so it can look into a low impedance input somewhere) which is ironic because it's probably hooked up to a new fangled "mid" impedance input on a servo balanced mixer input. (but I'm just guessing about that) I have to say... In the absence of some other suitable balanced output I'd ask you to place Y-chords on the (28dBu Max output) balanced Mains outputs. I'd want the full monty +4dBu balanced output that your mixer nominally provides. I would ditch the direct box and connect to the FOH mixer on its balanced line level inputs (via whatever snake/bay is used in your set up). I apologize for not paying better attention... I've got a new hobby. :-) very best, mike
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 13:55:43
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BTW is someone using headphones on the headphone output?
The block diagram suggests that the control room outputs and headphones share a driver stage? Which might further drag down the output of the "control room" output.
best regards,
mike
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The Maillard Reaction
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 14:29:26
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Oh and finally, I'm guessing the meters on your onstage mixer are much closer to tracking peaks than Volume Units...
The manual simply describes the meters as "highly accurate LEDs" The thought of an accurate diode makes me smile. The resolution on the faceplate shows one LED at 10dbU and then jumps to the next LED at 28dBu... honestly, that sort of undermines any notion of accuracy... don't you think?
Not to mention that a LED meter bridge is only as accurate as the parts QC anyways.
Which makes me wonder what sort of meters the FOH system is using.
In any event don't spend a lot of time worrying about the meters. :-)
best,
mike
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g_randybrown
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 15:14:31
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I would say I understood about 90% of your posts and then my brain started farting out loud so I had to give it a break. However you made me think about something I have ignorantly overlooked. The headphone jack...we do sequencing and I wear headphones. I brought up the headphone level (also control room ...which I'm sending the FOH) to a level I could tolerate andat some point assumed that was enough for him. I think the first thing I'll do at this meeting is unplug the headphones and give the FOH what it needs and hope it doesn't distort before reaching that level. Thanks Mike, you have been a huge help sir! EDIT: please let me know if you have any more suggestions!
post edited by g_randybrown - 2009/07/08 15:27:21
G. Randy Brown Windows 10, 64 bit, PlatinumIntel Core i7-3770S Asus P8Z77-V LK mobo 4X8GB Corsair XMS3 memory 500 GB Crucial BX100 SSD (OS)two WD Black 1 TB HDDSAPPHIRE DUAL-X 100314-4L Radeon HD 6970 2GB 256-Bit GDDR5 Presonus AudioBox 22VSLyoutube.com/crystalclearnm
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jcatena
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 15:40:56
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I'm coming out this board "control room" stereo, unbalanced to a 2 channel direct box. I noticed the feed on his end is coming in XLR on 2 channel strips but that's all I know.
Any advice will be very much appreciated, Send your balanced outputs to his channel inputs directly. DI boxes are not for this purpose, nor desirable. If his mixer doesn't have input pads, don't send more than +4dBu peak.
Jose Catena DIGIWAVES, S.L.
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g_randybrown
Max Output Level: -40 dBFS
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 15:59:35
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DI boxes are not for this purpose, nor desirable Really??? I thought they were for sending unbalanced line signal long distances to a board. So anyway, I haven't looked at his snake other than knowing it has some XLRs, can you be specific as to the ideal way to do this please? Thanks Jose, Randy
G. Randy Brown Windows 10, 64 bit, PlatinumIntel Core i7-3770S Asus P8Z77-V LK mobo 4X8GB Corsair XMS3 memory 500 GB Crucial BX100 SSD (OS)two WD Black 1 TB HDDSAPPHIRE DUAL-X 100314-4L Radeon HD 6970 2GB 256-Bit GDDR5 Presonus AudioBox 22VSLyoutube.com/crystalclearnm
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jcatena
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 16:14:10
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DI boxes are used to send high impedance unbal to a bal mic input.
You are sending a LOW IMPEDANCE mixer output, and you have also balanced outputs available, so you don't need a DI box.
Even if you use unbalanced outputs, you can also send them to a XLR mic input directly. You may need an adapter cable where in the source connector the -cable is connected to ground.
And you should, a DI box is a lousy device that should not be used when it is not required.
I did not notice you mentioned the DI box earlier: it is what's attenuating the signal (a lot).
Jose Catena DIGIWAVES, S.L.
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g_randybrown
Max Output Level: -40 dBFS
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RE: OT: Sensitivity vs gain, trim, pre-amp etc
2009/07/08 17:45:59
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ORIGINAL: jcatena
DI boxes are used to send high impedance unbal to a bal mic input.
You are sending a LOW IMPEDANCE mixer output, and you have also balanced outputs available, so you don't need a DI box.
Even if you use unbalanced outputs, you can also send them to a XLR mic input directly. You may need an adapter cable where in the source connector the -cable is connected to ground.
And you should, a DI box is a lousy device that should not be used when it is not required.
I did not notice you mentioned the DI box earlier: it is what's attenuating the signal (a lot).
Okay my friend please bare with me here: I don't have the manual with me but I would think that the "Control Room" stereo outs are balanced right? If that's the case I should just come out there with 1/4" balanced TRS to XLR all the way to the board no? Thanks again Jose you are a huge help here!!! Randy
G. Randy Brown Windows 10, 64 bit, PlatinumIntel Core i7-3770S Asus P8Z77-V LK mobo 4X8GB Corsair XMS3 memory 500 GB Crucial BX100 SSD (OS)two WD Black 1 TB HDDSAPPHIRE DUAL-X 100314-4L Radeon HD 6970 2GB 256-Bit GDDR5 Presonus AudioBox 22VSLyoutube.com/crystalclearnm
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