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Double Bass Dissonance when amplified

D

Dyfsunctional

Dec 1, 2006
10
1
57
Rockland County, NY, USA
#1
For years, I've got the distinct impression that certain notes--specifically C on the G string and F# on the D string--sounded vaguely out of tune, but only when amplified. I always thought it was either my imagination or my intonation to blame, but the other day I was playing with my volume pedal, did a little swell, and noticed the C had kind of a Leslie/synth organ feel to it when the attack was clipped off. My feeling is that my ears are hearing two different notes from the instrument and the amp.

I use a Rev Solo II into a Fishman Pro EQ preamp. The preamp has a "phase" switch, which essentially "flips" the wave to fight feedback. This had no effect on the problem. At the other end of things, my EA Doubler head has a more involved "phase" control, as well as a notch filter. Again, neither of these improve the situation.

Nobody but me can hear it, and it's super subtle. I have to remind myself not to subconsciously micro-adjust my left hand when it happens, because then I actually will be playing out of tune.
 
#4
Dyfsunctional said:
Nobody but me can hear it, and it's super subtle. I have to remind myself not to subconsciously micro-adjust my left hand when it happens, because then I actually will be playing out of tune.
Click to expand...

If no one else can hear it just be thankful it's not voices in your head instead.

Have you done any standard procedure troubleshooting like swapping the pickup to check the amp and swapping the amp to check the pickup? Borrow an Underwood and a different amp.
 
#5
Sounds most likely to me that your bass has some resonance either from the afterlength, or possibly the tailpiece, or somewhere on the bass that's not loud enough to hear acoustically, but is strong enough at the pickup location that it's being amplified disproportionally . If the TP is one of those coat hanger wires like they had installed on my Strunal when I first bought it, that'll make the problem worse...even more so if you're unlucky enough to get one of those horrible pressed aluminum tailpieces...
Other than Jeff's suggestions above, I'd try it out with some foam or whatever in the afterlength, check the fit of the pickup itself, try it with the enpin all the way out...maybe hold the TP rigid while you or someone plays the bad notes, and go from there.
 
#6
I'm actually having some difficulty reproducing this at home right now, which is a sure sign it'll be worse when I play at the next gig!

I've always kept a little pillow I had made tucked between the tailpiece and the bass for feedback. I think pretty much 90% of the feedback I've experienced has been either from the tailpiece or the afterlenghts (no surprise). I might get one of those little vinyl tube things to put between the strings, but i feel like that's just ugly, and probably does something to the tone of the instrument.

The tailpiece wire is newly installed, thick and braided. My luthier put it in without my asking him to the last time I had work done. The dissonance problem has been going on for years, though.
 
#7
I'll throw Link Removed into the mix as something to consider, although it may not explain what you're experiencing. :)

Add to that:
"Studies with the sounds of musical instruments show less perceived pitch change with increasing intensity. Rossing reports a perceived pitch change of around 17 cents for a change from 65 dB to 95 dB. This perceived change can be upward or downward, depending upon which harmonics are predominant. For example, if the majority of the intensity comes from harmonics which are above 2 kHz, the perceived pitch shift will be upward." (from this link, which I don't recommended for the rest of what's there)
 
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#11
I'll tell you one thing I've learned in speaker design. If there is a response resonant peak say 1/4 tone up from a note--- the note can stimulate that peak and that slightly higher resonant peak can ring out. I've had to go crazy at times cleaning up resonant peaks. They behave exactly like you describe. Did it get worse as your amplified volume increases?
 

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