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Combining Signals....volume loss

Discussion in 'Effects [BG]' started by Rumzini, Mar 26, 2006.


  1. Rumzini

    Rumzini

    Feb 14, 2004
    Jackson, MI
    Here is my current signal chain.

    Bass...tuner...Sansamp BDDI, (signal is split here)....one affected signal goes straight to a Morley ABY box then to MXR Micro Amp.....the other unaffected signal goes to an MXR M-80...Rocktron Moan/Wah...Chourus...Flange...Delay...then to the ABY/Micro Amp...then everything goes to my QSC.

    Reason for this of course is for the bass drop off from the wah. Everything would work beautifully except for when I want to combine the signals. If I play one or the other they are fine. However when I combine them...there is a compressed signal loss...low volume.

    I'm running the BDDI in the instrument level at this time...so it's essentially an effect right now, (not a pre amp). That's wht I have the MXR Micro amp for...a pre. All the tone shaping is done with the bass itself, M-80, and BDDI. Anyways...how do I get rid of this signal loss when I combine the two. If I could get the tubular valviness of the BDDI mixed with the ultra clean fat low of the MXR, and it's hyper distortion....Heaven.
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    One guess would be you are experiencing phase cancellation. To avoid that, you could use a mic pre with phase switching on one of the channels, or you could EQ each channel to occupy different ranges.
     
  3. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    IF any stuff is digital on one side or the other that could also induce phase problems as there can be a delay induced by ADC and DAC.
     
  4. Rumzini

    Rumzini

    Feb 14, 2004
    Jackson, MI
    ADC, DAC??? What does this stand for?
     
  5. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Analog-to-Digital-Converter - and you can guess the rest ; }
     
  6. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    What about (a) using a wah with no bass drop-off, or (b) splitting just the wah unit out a loop on the chain, so that only the frequencies passed by the wah are at risk of phase cancelling (no low end lost, anyway).
    Have you tried running them in series, without the splitting and ABY? AFAIK, the only way to run them in parallel without phase cancellation would be to do the phase switching or EQ trickery.
     
  7. bass-shy

    bass-shy

    Jan 11, 2005
    Florida
    +1 on the phase issue. Radial Engineering makes an A/B switcher with a phase inverter. It's called the Big Shot. I would swap the Morley you have now for the Radial. If you take it to Elderly Instruments in Lansing, you can trade in your Morley toward the cost of the Radial. It's around $69.00. This should solve the problem. Good luck.
     
  8. SubMonkey

    SubMonkey

    May 3, 2004
    Denver, CO
    Bass-shy's suggestion is a good one, I might suggest rigging up a reversed cable to test the theory before dropping the money on a new box.

    I use a whirlwind "selector" to do this function in my rig.

    http://www.talkbass.com/forum/attachment.php?attachmentid=26220&d=1133571495

    I use the Whirlwind Selector for the "combiner" function. I don't know if there's any magic there, but I doubt it...

    I'd be interested to know if Greenboy's idea is on, as in try removing any digital stuff from the chain as a test...

    I use a SansAmp GT-2 in the dirty side of my split, and an Aphex Punch Factory in the cleaner one... anyone know if those are analog/digital pedals ? (just as input on the ADC/DAC idea..)

    SM
     
  9. That won't work, unless you're system is entirely balanced and you're using XLRs or TRS jacks end to end.

    Same goes for that idea. The phase switch on a mixing desk or mic preamp only works for balanced signals.
     
  10. Jazz Ad

    Jazz Ad Mi la ré sol Supporting Member

    You need buffered lines to avoid feedback and phase cancelling.
    A Boss LS-2 for example.
     
  11. bass-shy

    bass-shy

    Jan 11, 2005
    Florida
    IIRC, the Punch Factory and GT2 are both analog. No conversion necessary.
     
  12. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Nifty, could you elaborate on that? I have owned unbalanced gear with (supposed) phase switching capabilities, but I don't have them now to look at the signals on a scope. I don't understand how/why using only two wires to convey an AC signal would prevent phase reversal. What's the scoop?
     
  13. jaffabass

    jaffabass

    Mar 28, 2002
    Don't get distracted by the idea that using digital effects on one side will introduce a shift in phase. I have a Boss LS-2 and if I run both channels in parallel, one side clean and the other with either my very analog Mutron or Meatball in low pass mode, I get the same loss of volume and bottom end.

    This is a problem any studio engineer comes across all the the time and the answer I have found from them is to simply eq the two signals differently, reducing the energy in the out of phase frequencies (in this case the low ones).

    In the LS-2 / Envelope filter setup I've tried, a solution is to put the filter into band pass or high pass mode, thus reducing a lot of the bass in that signal and therefore reducing the potential for phase problems in the low end.

    I'm not sure but I think our man Bootsy Collins may have run his pedals like this. I remember him describing having an un-effected signal thumping through a fifty foot stack of Crown power amps and then having his pedals feeding another couple of fifty foot stacks of the same Crown amps.
     
  14. Rumzini

    Rumzini

    Feb 14, 2004
    Jackson, MI
    At this point I'm sure that I'm just gonna go the split route into seperate channels and cabs. The low end from the MXR to the 212 and eerything else to the 410. Easy, simple, and I don't have to buy more gear.

    Also as far as the Wah is concerned, I've yet to find one that dosn't lose low end.
     
  15. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc

    Hey! - I've had that very problem! Don't negate what you haven't experienced ; } ...Luckily I figuerd it out very quickly. It's definitely something to consider though it may not be THE cause or the only cause ... Getting back to generalities, personally I wouldn't want ANY items or routing choices in my signal chain that are really playing havoc on freq response, phase, or transients.
     
  16. jaffabass

    jaffabass

    Mar 28, 2002
    Apologies Greenboy. I was just making the point that both analog and digital devices can cause weird shifts in the phase of a signal for whatever reason. It's just the nature of, what is essentially, the low accuracy electronics in an effects pedal.
     
  17. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    It's not that simple, Man.

    If there are phase cancellation issues when mixing signals, then you're just fooling yourself to think that you won't have cancellations in the air - they'll just manifest themselves as strange lobing in your dispersion, with hot-spots and dead-spots.

    Going to two cabs could be great, but FIX the phase problem first!

    Joe
     
  18. bass-shy

    bass-shy

    Jan 11, 2005
    Florida
    He's right. Although you may not notice it right in front of your rig, your audience will. It will appear as though certain notes disappear. The best fix would be to correct the phase issue with a transformer, like the one found in the Big Shot.
     
  19. Unbalanced signals can be phase reversed, but it takes more than just swapping the conductors around on the cable. It is most easily done by making a small, unity gain inverting amplifier either using a transistor or an op amp. A switch on such a piece of equipment would simply re-route the signal via the inverting amplifier thus flipping the phase by 180 degrees.

    Swapping the conductors on an unbalanced signal cable simply shunts the signal to ground via the shielding = no signal.

    Balanced signals already have a phase reversed portion built in. Three conductors, one is normal signal, one is phase reversed signal and the third is ground. By swapping the two signal cables, the phase of the signal is essentially flipped through 180 degrees. But, accidentally tie one or the other to ground (ie; swap the wrong two cables) and you loose half your signal level.

    (This is why when a sound engineer does a bodgey job of feeding a balanced signal into an unbalanced input he has to apply a lot of gain to get a usable signal.)
     
  20. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Ah OK, thanks for the explanation. Still, though, some of those channel strip units have 1/4" inputs on the front panel to accomodate use as a DI, and it seems to me that the signal would be converted to balanced at the preamp, then effectively phase-reversible. Of course the output would then be balanced, and it would have to be sent to a balanced input instead of an ABY pedal. Better in this case to use the Radial box or a home-made inverting amplifier box.
     

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