Help needed understanding the db numbers regarding gain

[Dan56]

Hello,

This post has been triggered by the issue of not getting enough out of a Yamaha MM8 key board going direct to the mixer. It goes out the Lt/mono out to a Radial Pro D2 to a Behringer SX4342FX board. The MM8 was maxed and yet I had to have the gain on the channel almost full and the fader above 0 to get enough, and no it was not loud. Unfortunately the rest of the guys did get louder as the last set came on. Any higher on the gain and it was at constant clip. It was a real struggle to find that balance as there was very little room. This left Marcel in the dark and to top it off, something went wrong with his ear monitor. He was blind to sound at the end.

I have no other issues with running mic's. I have tried running the MM8 to the line inputs and it seemed worse. I have not tried running the MM8 to the line inputs without the direct box because often we are outside and running through a 100ft snake.

So, I looking at using a converter that will boost the signal. Such as the Radial J +4: http://www.radialeng.com/j4.php or the Samson S-convert. But before I do, I would really like to understand what the spec's for my board mean.

The manual notes the following:
Gain has dual scale. 1st is +10 to +60 bB for MIC input. 2nd is +10 to -40 dBu for line input. It then talks of a "normal" line output level of -10dBV or +4dBu.

The specs at the end of the manual note:
0 ohm, -134dB/135.7 dB A weighted,
50 ohm, -131dB/133.3dB A weighted,
150 ohm, -129dB/130.5dB A weighted

Line input approx. 20kohm balanced, 10Kohm unbalanced Gain range -10dB to +40dB Max input level +22dBu @ 0 dB gain

So what does this mean as far as plugging stuff in? dB, dBu, dBV?

Unfortunately I have found nothing regarding the specs on the outputs of the MM8 and I'm wondering if they are much different from the headphone jack right next to it.

Thanks in advance for any help.

[sine143]

why not try running both Left and Right signals to the radial from the keyboard, this should net you 3db of gain. make sure the pad is not engaged (either via the button, or via a defect).

[Bruce Weldy]

why not try running both Left and Right signals to the radial from the keyboard, this should net you 3db of gain. make sure the pad is not engaged (either via the button, or via a defect).

The left output automatically does this if it's the only one plugged in.

Something else is wrong. Have you checked the software setup to make sure that the gain isn't compromised in some way?

Also, there is a pad on that direct box, make sure that it isn't engaged.

[sine143]

yes, but a phone plug (TS) naturally has 3 db less output than a balanced cable (TRS, which can be split into 2 phone plugs)

[Bruce Weldy]

yes, but a phone plug (TS) naturally has 3 db less output than a balanced cable

uhhh....Neither the plug nor the cable is balanced or un-balanced. That is determined by the device's output. I'm sure you know that, but the way you worded it may confuse some that don't.

(TRS, which can be split into 2 phone plugs)

If we are discussing balanced vs. unbalanced, then this statement is not true (if by phone plug, you mean TS). TRS plugs can be used as balanced cables utilizing 3 wire cable. TRS can also be used as a stereo feed (as in headphones). However, you can't split a balanced TRS into two unbalanced TS plugs (well, you can if you just utilize the hot and shield - but then it isn't balanced anymore).

No question that the balanced signal will be hotter than the unbalanced. But, when running a few feet into a direct box, then through the snake, the gain should still be enough to knock your head off regardless of the connection.

His problem looks to be something else other than whether he's running balanced or unbalanced. I've run crappy acoustic guitars with cheap pickups through passive DIs a thousand times - his keyboard should have plenty of gain.

He needs to use a process of elimination (after checking the pad switch on the DI and the setup in the keyboard) - plug a guitar into the DI and see if it has plenty of signal - if so, rule out the DI. Or, use another DI to see if anything changes.....

It's kinda' hard to screw up a passive DI - my guess that it's in the Keyboard setup, a bad cable, or a problem with that channel on the board (pad engaged, etc).

[Bill Fitzmaurice]

yes, but a phone plug (TS) naturally has 3 db less output than a balanced cable (TRS, which can be split into 2 phone plugs)

If a send has TRS capability, which is the same as XLR but with a 1/4" connector, it has 6dB higher output than if a TS is used, because the voltage is doubled. However, there must be a balanced input on the driven device as well. Using two unbalanced 1/4" outputs there is no voltage gain, being parallel sources.
The output of the keyboard is intended to drive a musical instrument amp, so it's mid level, and should have plenty of output. I suspect the problem is the DI box, which much be seriously padding down the signal.
I'd try making a 1/4" to XLR cord to go direct to the board, following the guidelines here:
http://www.rane.com/note110.html

[BrentEvans]

I'd try making a 1/4" to XLR cord to go direct to the board, following the guidelines here:
http://www.rane.com/note110.html

Presuming the board isn't running phantom power. While most balanced outputs are capable of handling the voltage, some devices shouldn't be connected to a mic pre with phantom engaged.

[Dan56]

Thanks all.

I do know the ins and outs of TRS, TS and XLR. The DI is transform isolated. There is a 15dB cut possible by switch, this was not engaged. I checked. I get patch cables also, that TRS to 2 TS cables. I'll check to see if I had the phantom power on. I might have because I was using two Behringer Ultra DI 100's which use the phantom power to provide the DI as an active unit. They worked, but the Radial allows me to use one compact unit for both his MM8 and Hammond SK1. I have no problems regarding gain with the mixer regarding his Hammond SK1 outs using the passive DI Radial (for the non organ voice that do not go to the Leslie).

I make my own cables and I make sure they are not damaged.

I have a TS to XLR cable I can try, but if it works, what do I do about a 100 ft + run? Also, I am assuming the output is the same on the MM8 whether connected mono or stereo. The outs were used to connect to his Roland keyboard amp but we are trying to get away from that and only have to bring the Leslie.

Can I check the output of the MM8 with my multi meter. Say, plug in a TS cable and connect the meter to get some idea of what it is putting out while rolling the volume control? What would I set it to? Volts? Amps? Hz?

I was hoping to get a bit of a lesson in understanding the various numbers regarding the gain specs of the board. IE: how is it that the mic has a plus to plus dB effect vs a negative to plus dBu effect for line? dB vs dBu vs dBV. I did just discover those large negative numbers regarding the mic are input noise specs based on resistance so not a concern for this issue.

I have scanned the MM8 manual, but I'm going to have to get into it more I guess. I have asked Marcel if there might be some kind of a volume programing that sets the max that the volume knob on the board will go to for the given program. He does not know.

Unfortunately, as I have noted in other postings, I am a one man show when it comes to the tech/sound of our band even though I have put every manual for every piece of electronic equipment in a drop box that all members have access to. I guess they are just musicians.

[dswpro]

I sense a few potential problems you could have.

First, your synth might have a low output for God knows what reason. Perhaps your patches are very delicate, perhaps your output op-amps have issues. Try the left, then the right, then the headphone jack to see if they are all the same level. Use a regular guitar cable ( single ended T/S 1/4 inch ) for the headphone jack if you try that output. Next, try using a different snake channel or mixer input. A problem in either can drop your input level significantly.

If you honestly just have a low level output you could use a small tube pre-amp ( usually less than a hundred dollars) in lieu of a direct box. This should give you lots of gain leaving the stage. I use one on certain acoustic instruments with pickups that do not output much.


Another suspicion for me comes in your statement:

The MM8 was maxed and yet I had to have the gain on the channel almost full and the fader above 0 to get enough, and no it was not loud. Unfortunately the rest of the guys did get louder as the last set came on. Any higher on the gain and it was at constant clip.

Does this mean that you were close to clipping the mixer input channel? If you can clip the input to your mixer, and you cannot get the synth loud enough in your mix, you may need to consider subtractive mixing. this is a fancy term for "turn everything else down".

Solo each input - look at the metering, listen to the levels. turn the GAIN down on other inputs which are washing out your synth. Adjust the monitors and house mix levels accordingly as this will change every monitor mix and the house mix. It is a difficult concept for a lot of FOH engineers to grasp. Sometimes you have to turn everything else down to get something you want up. Remember that during most sound checks, musicians play more quietly than when they have a crowd in front of them, so when you set gains, leave plenty of room for later.

Next time you do a sound check, try this approach- it usually works well for me. I tell the band I want them to just jam, or practice a couple songs while I ring things out. I tell them they will not have ANY monitors until I make sure all the inputs are working and get the house mix set. Most bands welcome extra rehearsal time and they always have parts to work out so they usually work well with this. After I get my house mix dialed in ( including turning DOWN the gains on things which might drown out other things) I start turning up monitors. First for any vocalists who aren't on ears, then instrumentalists.

See if any of these things work for you and good luck.

[Dan56]

DSWPRO,

Get them to turn down? I wish. Also, just to be clear, I'm trying to do all this while being the designated lead guitar.

But, I might have found the problem. The MM8 does have the ability to "edit" the volume on which ever voice is being used at the time. So I just sent Marcel the page numbers to read in the manual and offered to bring my sound analyzer so that we can get real volume levels.

The range of the control is Nigel Tufnel's (Spinal Tap) dream. Zero to 127. Who knows what that means, but it's 117 more than 10.

[Tom Smit]

The keyboard patches are one thing that I was going to suggest.

Another thing to try, would be to swap the inputs on the Radial, and then swap the outputs. As was suggested earlier, it could be cables or mixer inputs, as well.

[Rune Bivrin]

If you're actually able to drive the input channel into clipping I don't think the problem is with the keyboard or DI. However, the mixer - assuming you actually mean Behringer SX 2442FX - has a lot of ways to screw things up. What outputs are you using?

Also, there's the question of how the power amp is connected.

Is there anything between mixer and amp, such as a limiter or cross-over?

How's the gain/attenuation/sensitivity set on all these units?

You haven't missed the "Main" button on the channel, perchance?

In a trouble shooting situation you start by testing each unit separately. If possible you could connect the keyboard directly to the amp to see how that works.

The only thing that I see could be wrong in the keyboard would be very percussive sounds where the attack clips the input of the mixer but the average level is very low.

[Dan56]

Thanks Tom and Rune.

I have used other inputs and cables. The issue was not well known until the show this past Saturday. In practice there was always enough volume.

I think the input channel was driven to clip because the gain was set to almost full on. I think it was the board's channel driving it's self so to speak. The specs say +10 to +60 on the sweep. Well it was at almost full on. That's a lot of extra push of the MM8's signal before clipping.

The board is the SX3242FX as seen here: http://www.behringer.com/EN/Products/SX3242FX.aspx It is connected direct to the speakers which are QSC K series. (The BFM's are in stall mode while my cabinet maker/bass player finishes his 69 Camaro.) Nothing in between. The EQ is via main inserts. But, there was no issue with anything else going through the board. Plenty of sweep left on the dials.

No I did not miss the main button, though I did do that the first time I used the board outside of rehersal. I wondered why the effects were so strong.

We have practice Thursday so I'll get a chance then to see what the program volume is on the MM8.

[Bill Fitzmaurice]

My guess is you had the input sensitivity wrong. The gain on the XLR mic inputs is huge, because the output level of balanced mics is very small. For those occasions when an XLR input is used with a line level source, as is the case with a DI, there's a pad to knock the gain down. If your DI has a low output level it may be necessary to have that pad disengaged, using only the input gain pot to control the input level of that channel.

[Dan56]

So tonight I found the problem. It was a setting on his MM8. In this case, not the volume but the keyboard sensitivity. There are 4 settings. He had it set so that you had to pound the board to get volume. Once it was turned off, the drive was there. He was aware of that setting from another lessor Yamaha he has but never really understood how to check all these settings with the MM8 and then make sure they stayed that way.

Marcel now has his 6 main voice, all on bank one in order from 1 to 6. All set to equal volume, no clipping and plenty of room for him to work his volume pedal. No more hunting the list for the voice he wants to use.

Music director, lead guitar, soundman, tech guy. But, I don't sing so at least I don't have to be worried about that. Our new drummer is great. Tempo is right on. It is so relaxing.

Thanks for everyone's help. Much appreciated.