Signal Noise problem...

[ajrosales]

Need some help from a few folks that might be smarter than me...

In a live performance setting I've been experiencing a distorted signal at times, leaving me to resort to using a mic on my acoustic. The distortion is rather heavy. However, I'm not sure that I'm entirely able to understand the cause of it.

Here are the clues and details I know of:
Pickup: under the bridge Fishman transducer from the mid-90's
Culprits:
a) cable - I have a brand new cable and I've tried more than one new cable so I know this is not the problem.
b) battery - I just tested a battery with a multimeter (after experiencing this problem) and it was reading 8.72V. Is this drop in the voltage enough to cause this? I thought that these batteries were supposed to be ok with less than 8 volts. correct me if I'm wrong though.
c) 1/4" input: I cleaned the input recently with conditioning fluid so I know this is not the problem - unless there is something wrong with the parts inside?

post script: I played two gigs in the same day yesterday. The first one used one sound system and I did not experience any problems. The second one was a different venue and I had all sorts of distortion problems at that place. Is it possible that the battery voltage was inadequate or is there potentially some other culprit I'm not aware of here?

[YamahaGuy]

So many variables...
Did the second place have wedge monitors?
Were you using your own system at the place where you had the problems? If so, what is your rig?

Please tell us about the sound system/amp/stage conditions at the place where you had trouble so we can help get to the bottom of this.

[Big Band Guitar]

Batteries need to be tested under load.

The best way to test a battery is to replace it with a fresh battery.

Checking a 9 volt battery with a volt meter with the battery not in the circuit is pretty much meaningless.

[lschwart]

First thing that comes to mind is the input gain setting on the mixer's channel--assuming you were plugged into a PA system, but as YamahaGuy says, you need to describe the whole signal chain for us.

Louis

[ajrosales]

Originally Posted by YamahaGuy

So many variables...
Did the second place have wedge monitors?
Were you using your own system at the place where you had the problems? If so, what is your rig?

Please tell us about the sound system/amp/stage conditions at the place where you had trouble so we can help get to the bottom of this.

Both places had wedge monitors. But the volume on them was not enough to cause any vibration distortion. Neither of the rigs were mine - there were two different guys EQing and I didn't actually pay attention to the specs of the mixers, unfortunately. I don't have any details on the settings to provide...

They both seemed like fairly medium-quality mixers from glancing at them. Nothing pro is what I mean.

[ajrosales]

Originally Posted by Big Band Guitar

Batteries need to be tested under load.

The best way to test a battery is to replace it with a fresh battery.

Checking a 9 volt battery with a volt meter with the battery not in the circuit is pretty much meaningless.

How does one test under load? I've already changed my battery to potentially eliminate the problem tonight.

[ajrosales]

Originally Posted by lschwart

First thing that comes to mind is the input gain setting on the mixer's channel--assuming you were plugged into a PA system, but as YamahaGuy says, you need to describe the whole signal chain for us.

Louis

hmm that could be. I'll have to see if that is a setting that might be a problem if this happens again in an unfamiliar place.

also: I forgot to mention that the distortion comes (mostly) when strumming, as I do strum family hard (probably harder than most people). When plucking it doesn't seem to be as much of an issue...

[jimmorgan]

The most likely (but not only) scenario is that you're clipping the input on the mixer. The sound guy needs to turn the gain down on your channel.

[lschwart]

Originally Posted by ajrosales

hmm that could be. I'll have to see if that is a setting that might be a problem if this happens again in an unfamiliar place.

also: I forgot to mention that the distortion comes (mostly) when strumming, as I do strum family hard (probably harder than most people). When plucking it doesn't seem to be as much of an issue...

Distortion in sound reinforcement usually comes from a signal overloading the amp or preamp of the next stage in the signal chain. So, if whoever was in charge of the mixer had the gain setting on the guitar channel up a little too high, that might very well cause distortion on your loudest playing while leaving your quieter playing sounding just fine. Note that this doesn't mean that the volume coming out of the speakers would be extra loud. The level of the distorting channel preamp might still be attenuated by the channel fader. So you might have the guitar at the right level in the final mix, but with distortion occurring every time you play loud enough to overload the channel preamp.

If that's the problem, then the solution is easy. Just turn down the input gain on the mixer in question so that your loudest playing doesn't go into the red. It's worth also paying attention to the output control on your pickup's onboard preamp, if you have control of that.

It's possible, however, that it's something else--for example, something might be wrong with the piezo element under your saddle or with the way the saddle is sitting, etc. Or there may be something wrong with the preamp in the guitar itself. You just have to start with the obvious possibilities and eliminate them one by one until you find the source of the problem.

I will say that the fact that you got the problem in one situation and not in others suggests that the problem is somewhere in the PA system you were using and not in your own setup. And since you described the sound as distortion, the gain setting on the mixer input is a pretty likely cause.

Louis

[Kalani]

Yes, sounds like the gain/trim on the mixer is too high. You (or the soundman) have to mute the channel during sound check and you have to strum/sing the loudest you are going to during the performance and make sure the clip light doesn't light up red. If it does, just turn the gain/trim knob lower so you get yellow at most.

This forum has several great posts on setting your gain (gain staging)---very important.

Players will often sing/play really dainty and soft during soundcheck, then start wailing away during the performance. Then they can't figure out why they're distorting.

[pieterh]

Originally Posted by jimmorgan

The most likely (but not only) scenario is that you're clipping the input on the mixer. The sound guy needs to turn the gain down on your channel.

What he said. If it wasn’t happening at one venue and is happening at another with different gear then this is the first thing that should be checked. Strumming generates more signal level than picking or fingerstyle and a decent sound person should check gain structure with you playing your hardest/loudest.

[varmonter]

Originally Posted by Kalani

Yes, sounds like the gain/trim on the mixer is too high. You (or the soundman) have to mute the channel during sound check and you have to strum/sing the loudest you are going to during the performance and make sure the clip light doesn't light up red. If it does, just turn the gain/trim knob lower so you get yellow at most.

This forum has several great posts on setting your gain (gain staging)---very important.

Players will often sing/play really dainty and soft during soundcheck, then start wailing away during the performance. Then they can't figure out why they're distorting.

It's a secret trick .. If you sing or play softly at sound
check then when the real performance happens you'll be
louder than everyone else..(/sarcasm). ha!!

like said above it's all about gain staging. your
clipping somewhere.

[Vancebo]

I will offer a less likely but yet possible scenario. An under saddle piezo pickup distorts while strumming. It is the Natural occurrence of any piezo material under the pressure of the strings. This is known as piezo quack. The first sound guy knew what to do to minimize the quack effect, the sound guy at the next venue did not. Now, it’s most likely clipping at the input of the mixer but I thought I would mention it.

[ajrosales]

Thanks for the great replies - I haven't solved this yet but I'll try to figure it out based on these ideas. I think I understand a few things better now.

[Big Band Guitar]

Originally Posted by ajrosales

How does one test under load? I've already changed my battery to potentially eliminate the problem tonight.

If the fresh battery does not cure it then it is not the battery.

Testing under load means measuring the voltage while the battery is in the circuit and turned on.

Batteries can be thought of as a voltage source in series with a internal resistor (all inside the battery). As the battery ages the internal resistance goes up. This causes a larger voltage drop inside the battery so less voltage appears across the battery terminals. Only while in circuit. The more current draw the higher the voltage across the internal resistor and the lower voltage appears outside the battery.