weird sound problem


Well-Known Member
My school has a 16 channel Spirit 8. Today while I was running some mic cables for the talent show tomorrow I was playing the soundtrack to Wicked. I got to the end, and heard 2 vocal lines not come over the sound system. I investigated.

Now, before I go on, I should explain my school's odd sound system. The main out of the spirit board is going in as 2 mic inputs to a powered Peavey board, since we do not have any amps. The main out of that is running around the gym, right next to all of the lighting power cables, and to the speakers. Yes, we have horrible hum. Yes, I am working to get a snake to go under our gym, and yes I am working on getting amps, but for now, it works.

Anyway, back to the problem. I was listening to these lines, and was really confused that I didn't hear these two lines. These lines are high in the vocal range, so I assumed that going through the lines it lost the signal, or that the EQ was set incorrectly. I went into the booth and checked the settings of the sound board. On the Spirit 8 there is a button that you can push to run through the EQ or not, the button was up, so the sound was not running through the boards EQ.

I then checked through the headphones, checking whatever is coming out of the spirit 8 board. I did not hear the lines. I tried the same thing in a different channel, and yet again, did not hear the lines. Does anyone have any idea what could cause this, and why the soundboard does not want to use these sounds? The sound is inputing from my iPod, and I hooked up the headphones directly to the iPod, and it worked fine, so I know it is somewhere in the board.

For those with the Wicked soundtrack, it is "Thank Goodness", starting at about 3:27 minutes in, according to iTunes.
Hmm, after re-reading your post I see that the problem is those last two (high) lines in the song that don't go through. A number of questions: Are you using the headphones jack on the iPod or a line out (say, from the dock)? If it's headphones, what is the volume level on the iPod and the gain set at on the board? How is the iPod connected to the board, XLR or 1/4"? Have you tried connecting the iPod directly to the powered Peavey board to see if it's problem with the Spirit 8?

Edit: Have you tried burning the song to CD and running it off of that? what is the result?
I'm using a headphone jack. I took headphones and played it just through the headphones, and it all came through. Volume on the iPod was at about 60 or 70%. iPod is connected from a headphone out to 1/4 inch into the board. gain on the board is at 0. I have not tried going just into the peavey board.

I used the headphone out of the Spirit board and did not hear the lines, so it must be a problem with the spirit board.

I haven't tried burning a CD, but I'll try doing it tomorrow.
I would try using a different cable between your iPod and your board. When I used my laptop into a sound board I had the same really strange vocal dissappearance when I was using a small guage cable (It was a thin headphone cable with a 1/8th inch plug on each end, with an adapter to 1/4 inch standard audio on the end going into the mixing board.

The fix I will be using tomorow night when I am going to be DJing (see my post elsewhere for more on this) is simply to use a heavier cable between the laptop and mixing board. I stumbled onto this the first time quite by accedent, but now i go from a 1/8th inch (heaphone) output from my external sound card imediately to an adapter that switches it to 1/4 inch. I then use a normal "monster" cable (actually one that is borrowed from a friends electric guitar) to go from that adapter into my mixing board. Problem solved!

Note: the adapter I am talking about is very similar to the one on this page: although it is not exactly this one.
Let me see if I get this right. All the soundtrack is heard except for the last 2 lines?
I think that's right, Inaki2. It sounds really really close to the problem I was having. It seemed like interfearence from the rest of the music (especially base in my case) drowned out / canceled out the vocals. Maybe someone will have a better explanation of why this happens.... I would be VERY interested in hearing why this happens.
MM....well, yes, there is a psychoacustic property called frequency masking. Basically above a certain threshold, frequencies will cover up other frequencies.
Its weird that it happened on a recording like that, since someone would've noted it. And it's never so extreme as to completely mask it.
Another posibility is that if you were inputing it thru an unbalanced 1/4" input, and using a TS jack in the console end, you had phase cancellation due to the vocal being mixed in mono and the balancing circitry flipped the phase on your vocals. I've had this happen before. Its kinda weird sounding, as you only hear the reverb which is in stereo.
Inaki2 said:
Another posibility is that if you were inputing it thru an unbalanced 1/4" input, and using a TS jack in the console end, you had phase cancellation due to the vocal being mixed in mono and the balancing circitry flipped the phase on your vocals. I've had this happen before. Its kinda weird sounding, as you only hear the reverb which is in stereo.

More likely, to make the vocal sound distant, it may have been put on the two channels out of phase in the original recording. Through stereo headphones or speakers it's great, but mixing it down to mono, the out-of-phase vocals cancel.

I am just home from tonights gig, and I really quickly tested it out, and had the same type of vocal problem when using a thinner headphone type cable. I switched it to the heaver cable and it worked fine for the rest of the night.

Random comment:I should have gotten pics of the whole setup tonight, I was running from my laptop into a mixer then from that into a mixer->amp chain for the gym's built in speakers, and also from the primary mixer into a PA system type mixer that powered 6 aditional speakers (nearly all the speakers from our auditorium, including the monitors) I had an Aux out of the mixer in to a friends laptop's Mic In port, and had that laptop runing g-force (a cool free visualization program) through a projector. This projector was aimed through a blanket of rising fog that I chilled in a homemade custom fog chiller, so the fog rolled allong the ground out of a cemetary scene that had been made, when it left the cemetary the smoke drifted up into the beam of the projector making a REALLY neat effect. All together it was probabaly the neatest dance in our school's history.

Anyway, now that I am WAY off topic, I got the whole rig working with decent sound quality by using heavy 1/4 inch cable on every connection.
thats weird, ussually cable wouldn't kill anything that much. Have you changed connectors as well as the cable? At the vry most it could be the impedance or capacitance of the cable, but its almost unnoticeable, even more so in such a short run.
I'm leaning more towards the conector side.
I am not really sure what you mean by changing connectors. I only have two of those heaphone cables, and both of them did it so I am really puzzled. There is a chance that the input on my mixer or the ouptut on my soundcard are not making the best connection, at some point when I extra time (haha, like that ever happnens!) I'll fool arround with it abit more. I am fairly sure that it only happened with really heavy, loud, bass intensive music, I dono if that helps anyone with ideas. How "intense" of a song is the song you were playing zac?
I mean, did you have a TRS (aka "Stereo") connector on the console endo or a TS (aka "Mono") connector? What both DMXTools and I are aiming at is that due to the way that the track was recorded, by using one of the connectors, the vocals may have cancelled out on themselves or by the console's input system.
So let me have these 2 pieces of info from you:
1) What type of channel were you going into? Was it a normal console channel (ie: Mic & Line) or a dedicated stereo channel with both jacks for L & R?
2) If going into a normal channel, what connector did you have on the console end? If going into a stereo channel, what connector or adapter/cable did you have on it?
Hmm YA!!! that makes sense, it was a sterio cable right from start to finish, and it was into a line input on my board. Maybe that was causing a problem. My board doesnt have any sterio inputs except one tape in, but that input only goes streight into the main with only one volume knob between the input and the master fader. (So i cant send it to my monitor speakers running on an aux channel) I'll have to try it with a sterio to mono adapter, and mabye a sterio to two mono adapter if i can find one. (our school has NO adapters of it's own, so i only have what i have in my growing personal collection)
I think that what Peter sugested is going to work, simply based on that everything he said is true. I'm going to try burning it onto a CD and seeing if the lines show up.
Yeah there you go. Here is what I make of it and I'll try to explain it so it makes sense. I am, by the way, a really sucky teacher.
The line inputs on your console are balanced. The way balanced inputs work, when there is no transformer present, is by using an Op Amp (Operational Amplifier) in what is called a Unity Gain Inverter circuit. basically what this does is flip the phase on Pin 3 in an XLR (or Ring on a TRS), and when summed with Pin 2, all noise in the line is cancelled because you have them 180 deg. out of phase with each other.
By placing the output of your IPod or whatever device into the channel, what you did is flip the phase on one side of the stereo spectrum. (I think Ring is Right) Thereby, anything mixed in mono would then cancell out as it is being summed to the Left channel also, which is 180 deg. out of phase with the Right channel. The fact that yo may hear the reverb tails only is because most effects are stereo, and they would not be cancelled.
If you need more explaining, please ask, I'll be happy to get into more detailed things.
As a solution I would NOT recommend the Stereo-Mono adapter, but a Stereo to double Mono adapter, that way you can get the Left & Right channels onto separate input strips, and pan these hard left and right (or wherever you may please if you don't have a stereo system in you auditorium). You'll get much more clarity, dynamic range and oh yeah, the vocals back!
I don't think I did.

The way it was set up is that left channel went into one channel, which was panned hard left, and the right channel went into another channel, which was panned hard right.

I think, as was sugested earlier, that it is the cable. I'm going to try burning a CD and seeing if I here the lines.
Hmm, ya I understood that too! Thank you. It kinda sounds like we might have a slightly different problem if you are running your iPod into a sterio input. I know i was definatly not.

To restate what you said Ignacio, bascily what is happening is the same exact thing that happens when you run the same track through two chanels of an audio editing program and push the invert button on one of them.

It makes perfect sense that that would be what is hapening, my only question now is why was I not noticeing it more and for other songs. I get REALLY noticeable results for just about every song I invert in different Audio software I have, what I heard from my system was no where as extreme as the software results.

Thanks for the help!
Well, Phase cancellation depends on how the songs are recorded, some others may have the vocals panned or one of the most popular is to have 2 vocal tracks at the same time, panned left and right. There a number of reasons why the cancellation is not extreme in all tracks. Besides, you may have gotten vocals cancelled out, but maybe still heard background vocals or short reverb tails and didn't notice the vocals missing.

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