phase aligning a DI with a mic on amp in a live situation

[Killspringer]

I'm a bass player who makes my living from live sound and recording. In recordings, its always great to phase align the DI of the bass with the mic on the amp. Since they'll be a few milliseconds apart you just slide the mic'ed waveform forward in your DAW. If you're using tape you can use something like the little labs phase aligner and your ears to do the same job:

Little Labs

I know there are venues with real nice sound setups that have this box. I was wondering if there were any bass players who had something like this in their rig and work with the soundman on achieving a better mic/DI blend this way, or if any soundmen can chime in on working with somebody who had this in their rig. Did you think it was worth the $, space, and time during soundcheck? I figured that unless there's a drastic tempurature or elevation change from the last show, it would work on the same setting for each gig since my mic clips the same distance from my cab every time, plus or minus a centimeter or two.

I am touring with my music man Big Al running into the house out of my Eden WT DI and an RE20 clipped onto my cab. Thought about adding the little labs box to my aresenal of over-the-topness.
I'm kind of new here, apologies if this is an old topic.

 

[fokof]

I use this one :
[Invalid or Expired Link Removed]

I use it all the time when doin sound.
Also practical in various situations : 2 mike kicks , OH , grand piano , etc...

Very usefull tool.


I have yet to see a place with one of these in the rack. Heck , majority of tech don't know it exists !!!

 

[fokof]

Thought about adding the little labs box to my aresenal of over-the-topness.
I'm kind of new here, apologies if this is an old topic.

I'm a soundman and it's a "must have" tool. But I'm also a bass player.

When I gig as a bass player , I'm DI all the time so I use it to cancel annoying frequencies between my monitor and the PA wich sometimes happens onstage.
I send a clean signal in front and pass through the Phazer just before my active monitor.
(Or else , it wouldn't do nothing .... doh! )

Your soundman should have one , it's more his "area" than yours. If you guys have a digital board , problem solved !

 

[testing1two]

These types of boxes are used to cure two different bass phasing issues in a live setting: first, to align the phase between the DI and mic by delaying the DI signal and second, to align the phase between the player's amplifier and the PA subs by delaying both the DI and mic.

The first is easy because the relationship between a DI and a cab mic are fixed provided you mic your cab the same way every time. The Radial or Little Labs devices should work great for this purpose and you could even keep them onstage with you. The second is not so easy because the distance between your amp and the PA changes with every venue which changes the required phase adjustment/delay time. It is also dependent on how much your amp can be heard by the audience. In this scenario, the phase needs to be adjusted at the mix position (very easy to do with a digital console).

 

[fokof]

These types of boxes are used to cure two different bass phasing issues in a live setting: first, to align the phase between the DI and mic by delaying the DI signal and second, to align the phase between the player's amplifier and the PA subs by delaying both the DI and mic.

Just to use the right terminology ; these units doesn't add delay , its a phase shifter. Not the same thing.

The second is not so easy because the distance between your amp and the PA changes with every venue which changes the required phase adjustment/delay time. It is also dependent on how much your amp can be heard by the audience. In this scenario, the phase needs to be adjusted at the mix position (very easy to do with a digital console).

In this scenario ,for the FOH guy , a delay is a better tool to align "distances".
But a Phazer can also do the job , or help a lot anyways.



IME When I use it onstage as a bass player it can be usefull because the ringing frequencies onstage are not always heard in front. It gives a level of "freedom" to kill those without EQ'ing.
Important to note that it's not the magical solution to all problems onstage , there can be lot's of low frequency sources creating these problem.

 

[steveksux]

Just to use the right terminology ; these units doesn't add delay , its a phase shifter. Not the same thing.

Actually, that IS the same thing. You're adding the appropriate fraction of a wavelength of delay to one signal so the two signals are in phase with each other.

Randy

 

[fokof]

Actually, that IS the same thing. You're adding the appropriate fraction of a wavelength of delay to one signal so the two signals are in phase with each other.
Randy

The way I understand it, correct me if I'm wrong:
It is not a Delay principle but a 0°-360° principle.

10ms delay to a signal will move it in space. All frequency equally.
A 76° phase shift will not do the same thing to a 100Hz than to a 1Khz relative in time

180° to a 1khz signal is what ? 0,005ms?
180° to a 100hz signal is what ? 5ms?
Not the same thing......

 

[steveksux]

The way I understand it, correct me if I'm wrong:
It is not a Delay principle but a 0°-360° principle.

10ms delay to a signal will move it in space. All frequency equally.
A 76° phase shift will not do the same thing to a 100Hz than to a 1Khz relative in time

180° to a 1khz signal is what ? 0,005ms?
180° to a 100hz signal is what ? 5ms?
Not the same thing......

True, but if you're talking about correcting phase due to distance from mic to speaker or bass amp to subwoofer, then you want to shift the signal in time, a delay equal to the time it takes sound to go the distance between them. That's the context I was referring to, what the thread was about.

Randy

 

[walterw]

makes sense. the slight time delay is what you're actually correcting for, while (thinking and typing here) maybe rotating the phase of one of the signals might fix the problem with the lows but not the highs, or vice versa.

you could end up with one frequency range in-phase with the other, even though the whole waveform is a cycle or two behind.

 

[ugly_bassplayer]

Why not just reverse polarity on one of the 2 if there's a phase problem.....click problem solved.

 

[walterw]

polarity is not phase!

you could be somewhere between "the same" (0 deg) and "the opposite" (180 deg), in which case flipping polarity won't do it.

 

[Killspringer]

Thanks for the replies everybody. Sounds like I opened a can of worms. As walterw put above, i was also "thinking and typing" when I wrote this thread. A couple ideas...

The second is not so easy because the distance between your amp and the PA changes with every venue which changes the required phase adjustment/delay time. It is also dependent on how much your amp can be heard by the audience. In this scenario, the phase needs to be adjusted at the mix position (very easy to do with a digital console).

Correct me if I'm wrong, but after about 12 feet between mics or sources the timing differences will be experienced psycho-acoustically as ambiance, not phase, and is no longer technically phasing. Forgot exactly how this works mathematically, but it is explained very well in a book called "The New Stereo Sound Book". If your amp is less than 12 feet from the PA mains, then yeah, maybe... This is not to say that using a phase aligner in this case would not make it sound better, but is that technically phase? Maybe this only applies for two mics 12 feet apart in a recording situation? I'll have to think about the science behind that a little...

The way I understand it, correct me if I'm wrong:
It is not a Delay principle but a 0°-360° principle.

Great point. I guess it is a 0-360 thing, and isn't really adding more than a tiny tiny bit of delay. There is a delay knob on the IBP but I think it only goes to 4ms. Not sure if that's enough to really move things back in time enough. I'll have to do some math on tuesday when I've had a full night of sleep

Unfortunately, my band isn't playing a lot of places yet where the sound dudes are as smart as you guys, have phase aligners, and digital consoles. One day... until then maybe I'll check out that Radial box.

 

[fokof]

IME when mixing FOH , if I want to put the backline and the PA "in line" , I use a delay , but if I want to correct multiple sound sources from a single instrument , DI + mike , OH drums, grand piano , front+ back kick mike , 2 mikes on a Clarinet or baryton sax etc..... I use a Phazer.
YMMV

 

[Killspringer]

IME when mixing FOH , if I want to put the backline and the PA "in line" , I use a delay , but if I want to correct multiple sound sources from a single instrument , DI + mike , OH drums, grand piano , front+ back kick mike , 2 mikes on a Clarinet or baryton sax etc..... I use a Phazer.
YMMV

Yeah dude, thanks. That seems to be what my research and advice around town is telling me. I want to try this out cuz i hear so many engineers mess up the DI/amp blend, and when the attack is spot on, the whole room is just way more solid. The IBP has a delay knob on it that goes from 0-4 ms, so if it takes 1ms for sound to travel a foot, i should be covered if the phase knob doesn't do enough.

 

[steveksux]

IME when mixing FOH , if I want to put the backline and the PA "in line" , I use a delay , but if I want to correct multiple sound sources from a single instrument , DI + mike , OH drums, grand piano , front+ back kick mike , 2 mikes on a Clarinet or baryton sax etc..... I use a Phazer.
YMMV

Not following why that's different. The 2 signals from the same instrument are different based on their distance to the instrument. Mic is a little bit away, the DI is essentially right there. That's still a time delay isn't it?

The mic may have phase issues in its response I suppose, THAT could be compensated for by the right phase shift at a certain freq. Each mic would be different, how do you know what freq and how many degrees to shift for each mic?

Randy

 

[rockstarbassist]

I've never had anyone live tell me they could hear the audible difference in a loud, PA, blasting Mesa Recto + drums setting fwiw between the two signals.
And even through my in-ears I can't tell even when I try to find it.

 

[fokof]

Not following why that's different. The 2 signals from the same instrument are different based on their distance to the instrument. Mic is a little bit away, the DI is essentially right there. That's still a time delay isn't it?

Phazer is to put in phase 2 diffrent sounce of a single instrument if sources have a different "tone"
Not necessarily a distance thing (delay) but a "tone" thing
Like a front and back mike on a kick , both will pickup up a very different tone , I'm better served with a phazer than a delay. A DI and a Miked amp , it's a "tone" thing , not a delay thing.
Yes you can get away with a delay but calculate the right amount is a bit complicated and a lot of gear don't give you 0,1 increments. IME it's A LOT easier with a Phazer/IBP , just by ear.

If a bass amp is loud onstage , it can create phasing issues in front then a delay is the right tool 'cause it's a single "source" opposed to the PA.

In resume , a phazer is a better tool to match multi sources/tone of a single instrument.
A delay is a better to align in space @ the FOH position.

YMMV
(I don't hold the holly thruth)

 

[fokof]

I've never had anyone live tell me they could hear the audible difference in a loud, PA, blasting Mesa Recto + drums setting fwiw between the two signals.
And even through my in-ears I can't tell even when I try to find it.

So it's either that your soundman has set it up properly or that you WOULD hear a difference if he do it right.

With a HPF on the mike and a LPF on the DI setup at the same frequency you can get away with it too.

And no , my mother don't hear a difference either .......

 

[Munjibunga]

Why not just reverse polarity on one of the 2 if there's a phase problem.....click problem solved.

So you change the phase 180°. What if the two signals are, say, 72° out of phase?

 

[Killspringer]

I've never had anyone live tell me they could hear the audible difference in a loud, PA, blasting Mesa Recto + drums setting fwiw between the two signals.
And even through my in-ears I can't tell even when I try to find it.

that's because you've never known anybody who's phase aligned a DI with a mic in a studio situation and realized how much better it was than a non-aligned bass mix. try it some time. record a DI and a mic into pro tools, zoom in ALL the way, and drag the mic'ed waveform forward until the zero-crossing of the first transient of the waveforms line up perfect. now A/B the before and after and tell me it doesn't sound better. why people don't do this live?!? I dunno