Two signals out of phase.

[RhythmBassist01]

I'm considering a purchase of the M-Audio USB MobilePre.

My question is, if I mic the amp and record DI Simultaneously, is there a possiblilty that the two signals will be out of phase?

If so, is there a way around this using the USB MobilePre?

 

[Wrong Robot]

By 'out of phase' are you referring to a lagtime between when you play a note and when it is recorded and/or played back in your monitor?

that's typically referred to as latency. If I'm following you correctly. Latency is typically not an issue if you're just recording one instrument at a time. But if it is, it's usually CPU related first and interface related second. M-audio doesn't **** around with their interfaces and wouldn't put something on the market if it was going to consistently be a pain in the ass to work with(okay, so they've had some sketch products in the past, but their kicking ass these days)

Remind me, does the mobilepre use USB 1.1 or USB 2.0? If it uses 2.0, you won't have any issues with latency at all. If it uses 1.1, there is a slight chance, but I'd say it's thin at best if you're only recording one input at a time.

if you're using multiple inputs(forgive me if I didn't follow you correctly) then there is a greater risk of having things fail to line up, but again, it'd probably be your CPU failing to keep up before the interface fails.

Lowering the quality settings is a sure fire way to reduce lag, but that's upto you if you can accept that.

 

[Oysterman]

My question is, if I mic the amp and record DI Simultaneously, is there a possiblilty that the two signals will be out of phase?

Well, there's always a possibility, but it's very easy to fix. Usually the mixer part in (most? all?) recording software has a phase switch on each track. Hit the switch on either track and the problem should go away.

Sometimes this phase switch does too much though, the phase problem is subtler than can be remedied with a full "180" switch. If that's the case, it's just a matter of offsetting one of the bass tracks the tiniest bit, by dragging and dropping the clips in the software. You can even do it visually, just watch the two waveforms that cause the phase problems and make them line up. But don't forget to let the ears be the true judge of whether the phase issue's gone or not.

 

[C-5KO]

I'm considering a purchase of the M-Audio USB MobilePre.

My question is, if I mic the amp and record DI Simultaneously, is there a possiblilty that the two signals will be out of phase?

If so, is there a way around this using the USB MobilePre?

If you're running plugin's there's usually one that can phase reverse the track also.

 

[RhythmBassist01]

Thanks for the ideas everyone. I probably need to upgrade my computer as well.

 

[hyperlitem]

i was under the impression that you could only go "out of phase" when using microphones. You must set mics 5 times the distance apart as they are to the surface i beleive, its either 5 or 8 times. Besides that ive never heard of anything being out of phase such as DI's.

 

[Oysterman]

Thanks for the ideas everyone. I probably need to upgrade my computer as well.

That depends. What do you have now?

(You really don't need that much of a computer, by today's standards, to record and mix some music. I've done it on a PIII 733 MHz PC with 256 MB RAM, and I could have gotten by with less.)

 

[Oysterman]

Besides that ive never heard of anything being out of phase such as DI's.

Not a DI on its own, but a DI paired with a mic'ed track could. The delay caused by the sound traveling from the speaker to the microphone can put it out of phase with a direct recorded track, depending on how the mic was placed. Though I wouldn't say it's very likely to happen if put it close enough to the speaker cone. At least it's unlikely to be noticeable.

 

[RhythmBassist01]

That depends. What do you have now?

(You really don't need that much of a computer, by today's standards, to record and mix some music. I've done it on a PIII 733 MHz PC with 256 MB RAM, and I could have gotten by with less.)

As a matter of fact that's what I have now. Do you think I could continue recording and mixing with these spec's? It's not the fastest, but what I'm more concerned with is quality, hence the purchase of USB MobilePre. what I'm also interested in is sampling, in particular the GigaStudio software, and the minimum spec requirements for it.

 

[Oysterman]

Quality as such wont suffer just because your computer is a bit old, but your working conditions might to some extent. The main gripe I had with my PIII was that it wasn't powerful enough to run all the DX/VST effects I wanted in real time (e.g. Waves RVerb ate 50% of the CPU overhead just like that). The workaround is simply a matter of bouncing a 100% wet track of the effect you want, and mix it in with the dry track. While this is simple enough to do, it does take some time and in the long run working like that might annoy you a bit.

With GigaStudio, low processing power will mainly hamper your polyphony. GigaStudio will work with your computer, no doubt, but it's not like you'll get 200 voices or anything. But I suppose you could do the bounce-to-track workaround with GS as well.

I guess there's no doubt that faster is better when it comes to computers. But if you're short on cash, or at least able to find better ways to spend your money than a new computer, you could try using your PIII for a while and see how it works for you. If it doesn't, a used P4 most likely will, and shouldn't set you back a whole lot.

 

[Lyle Caldwell]

Let's not confuse phase with polarity. Polarity means 180 degrees out of phase - total cancellation. Usually you won't get 180 degrees out of phase with a mic and a DI. So flipping the polarity of one track will just give a different kind of out of phase sound.

In that case, you want to time-align the tracks in your audio program. Find a noticeable transient attack on both tracks, and slide the miked track back until its transient aligns with the DI transient.

Also note that people combined mics and DIs for decades before the ability to slide tracks existed, and people got lots of great sounds on record. It's not always crucial.

 

[RhythmBassist01]

Quality as such wont suffer just because your computer is a bit old, but your working conditions might to some extent. The main gripe I had with my PIII was that it wasn't powerful enough to run all the DX/VST effects I wanted in real time (e.g. Waves RVerb ate 50% of the CPU overhead just like that). The workaround is simply a matter of bouncing a 100% wet track of the effect you want, and mix it in with the dry track. While this is simple enough to do, it does take some time and in the long run working like that might annoy you a bit.

With GigaStudio, low processing power will mainly hamper your polyphony. GigaStudio will work with your computer, no doubt, but it's not like you'll get 200 voices or anything. But I suppose you could do the bounce-to-track workaround with GS as well.

I guess there's no doubt that faster is better when it comes to computers. But if you're short on cash, or at least able to find better ways to spend your money than a new computer, you could try using your PIII for a while and see how it works for you. If it doesn't, a used P4 most likely will, and shouldn't set you back a whole lot.

Thank you veru much for the advise.

Thanks to everyone else for ideas and comments.


TB Rocks!

 

[Petebass]

Only yesterday I was reading an article in Audio Technology magazine (Issue 42). It was about recording bass and was written by ledgendary Australian engineer Mark Opitz, known mostly for his work recording INXS:

"..it's vitally important to investigate the in-phase characteristics of the recorded bass signals visually as waveforms. What sometimes happens with amp/DI combinations is that the phase alignment problems can work against the production of full range sound because the DI signal is arriving at the recording device slightly ahead of the miced signal (depending on the distance of the mic from the speaker). When these two "versions" of bass are mixed together, their phase anomalities can weaken the sound, wash it out, making it sound thin and ugly. But with the power of digital recording at our disposal, the accurate re-alignment of these two waveforms can be addressed, producing a full and powerful bass sound."

Unfortunately the article doesn not go into detail about exactly how to do this. He goes on to say he records a DI track even when recording guitars, using it later to check the digital waveform at a later date and address any phase issues created by mic placements, effects, whatever.

As mentioned earlier, the distance of the mic from the amp comes into play. The closer the mic, the less phase shift. "However, as we all know, the physical lengths of bass frequencies is much greater than top end frequencies. So in order to capture them, you need the mic a bit more breathing space from the speaker. But, of course, with most mics, when you do this, the mic loses focus and effectively becomes a "room mic". rather than a "front-end" mic"

He recommends EV RE20 mics in this situation, because they have anti-phase tubing down the sides, and they're shotgun-like rejection that helps everything stay focused. He has a lot of things he likes about this mic. He's also uses the Neumann U47.

 

[BulkHead]

Also note that people combined mics and DIs for decades before the ability to slide tracks existed, and people got lots of great sounds on record. It's not always crucial.

I've done it since the '80s, and it always worked on tape. Maybe now that we can actually see the wave form, ppl are starting to pontificate, problem is: when you mic it properly (experiment while you listen in the cans to both the di and the mic, put the mic in the right place and it all comes together) Mic placement is not mystical, move it around until it sounds good.

 

[justmybass]

Hi everyone, this is actually a subject i've talked a lot about in my recording classes at school, phasing is a big issue when making good quallity recordings, becasue if your not carefull you can elliminate key frequencies that you really want.


hyperlitem said earlier "You must set mics 5 times the distance apart as they are to the surface i beleive, its either 5 or 8 times"

this is correct and incorrect. the rule your thinking of is the 3 to 1 rule. same idea you had when using two mics the mics have to be at least 3 times the distance apart as they are from the sound source. (Ex. mic 1 is set 1 foot from the sound source so mic 2 has to be 3 feet away from mic 1)

back to the original question, using a mic and a DI can create phaseing problems. someone said something like this earlier i think, but it's worth repeating, the DI signal will reach the tape slightly before the mic signal, so when the sound waves form the composit wave the some frequencies will be cancelled out and won't be heard.

so to do a recording with a DI and mic the best thing to do is wear a set of headphones and play with the placement (moving it further or closer to the speaker) of the mic while playing through the amp (so that the DI signal and Mic signal are both in mono set at the same level in the headphones) when the mic is in phase with the DI the sound in the headphones will sound full and should have the full range of frequencies with out any missing. you have to be carefull because those low frequencies can cancel out quite easily.
another thing is i think some software or plug-ins might allow you to zoom in on the sound wave all the way to the sample rate. if you can do this you can zoom in and then move the track slightly to "re-phase" the tracks.