Mic & DI recording

[Dirty Soul]

Hi everyone (hope this is in the right place - 1st 'New Topic')

I’ve been recording for a number of years now (not for this whole time of course!)

When it comes to bass, I like to record the DI from the back of my SVT-3 & use a large diaphragm condenser mic around 9” (oo-er) away from the cone of a Ampeg SVT-410 HLF cab. Both sent to separate tracks in Pro-Tools.

I’ve never been able to achieve the specific results I wanted although it’s never sounded too bad………….now I know why!

Apparently the signals are slightly out of time with each other! The mic signal is delayed slightly because of the time taken for the sound to travel from the speaker to the mic (around 1 millisecond per foot travelled). When the 2 signals are mixed it results in undesirable comb-filtering! See this article in Sound on Sound: [url="http://www.soundonsound.com/sos/jul01/articles/micdi.asp"]Phase Matching DI & Mic Signals[/url]

Having learnt about this, I went back to Pro-Tools on the tracks our band are currently working on and put a delay on the DI signal of 0.9 milliseconds – and lo and behold………. A BEASTLY full, deep, consistent sound. I’ll try and upload some audio if I can.

Just though I would share this tip with everyone and wondered if anyone else has experienced this??

[Wil]

I think some mics have a phase reversal switch on them, not quite sure how this works, but I guess it's to combat this problem. Never realised it was due to the tiny delay between the sound leaving the cab and hitting the mic, though! Interesting.

[51m0n]

[quote name='Dirty Soul' post='800785' date='Apr 9 2010, 12:57 PM']Hi everyone (hope this is in the right place - 1st 'New Topic')

I’ve been recording for a number of years now (not for this whole time of course!)

When it comes to bass, I like to record the DI from the back of my SVT-3 & use a large diaphragm condenser mic around 9” (oo-er) away from the cone of a Ampeg SVT-410 HLF cab. Both sent to separate tracks in Pro-Tools.

I’ve never been able to achieve the specific results I wanted although it’s never sounded too bad………….now I know why!

Apparently the signals are slightly out of time with each other! The mic signal is delayed slightly because of the time taken for the sound to travel from the speaker to the mic (around 1 millisecond per foot travelled). When the 2 signals are mixed it results in undesirable comb-filtering! See this article in Sound on Sound: [url="http://www.soundonsound.com/sos/jul01/articles/micdi.asp"]Phase Matching DI & Mic Signals[/url]

Having learnt about this, I went back to Pro-Tools on the tracks our band are currently working on and put a delay on the DI signal of 0.9 milliseconds – and lo and behold………. A BEASTLY full, deep, consistent sound. I’ll try and upload some audio if I can.

Just though I would share this tip with everyone and wondered if anyone else has experienced this??[/quote]

Since you are in pro-tools, cant you just move the entire set of objects on the mic track forwards to get them in time and as on the beat as the DI??? By moving the DI back you are getting a lazier take (although at 0.9 ms its not going to be noticeable, but if your mic were further away it would become more and more noticeable).

I always try and get a device to pump a tone into the jack that plugs into the bass, run everything up to get channel levels, and a good basic position for the mic, then get eyeline on a meter and move the mic until you get max output on the meter. Job done!

[Dirty Soul]

[quote name='Wil' post='800791' date='Apr 9 2010, 01:01 PM']I think some mics have a phase reversal switch on them, not quite sure how this works, but I guess it's to combat this problem. Never realised it was due to the tiny delay between the sound leaving the cab and hitting the mic, though! Interesting.[/quote]

I think Phase reversal on mic's (and pre-amps) tends to be if you have 2 mics facing each other with the sound source in between (i.e. mic'ing the top and bottom of a snare or back and front of a kick drum)
The delay is obviously so small I never noticed the difference either, I just knew it didn't sound right.

[Dirty Soul]

[quote name='51m0n' post='800797' date='Apr 9 2010, 01:05 PM']Since you are in pro-tools, cant you just move the entire set of objects on the mic track forwards to get them in time and as on the beat as the DI??? By moving the DI back you are getting a lazier take (although at 0.9 ms its not going to be noticeable, but if your mic were further away it would become more and more noticeable).[/quote]

I might try that. I was monitoring the Mic signal (at the pre-amp stage) and not the DI when recording so it might be slightly ahead of the beat - not sure definitely some experimentation required!

[quote name='51m0n' post='800797' date='Apr 9 2010, 01:05 PM']I always try and get a device to pump a tone into the jack that plugs into the bass, run everything up to get channel levels, and a good basic position for the mic, then get eyeline on a meter and move the mic until you get max output on the meter. Job done![/quote]

Now THAT is a good idea! Thanks for sharing

[cheddatom]

I read that article ages ago. I just try and line them up as best I can in cubase. Monitoring both at the same time while looking at a meter is a brilliant idea which i'll be stealing thankyou!

[51m0n]

Thank you thank you, I'm full of it, sorry them

[Bankai]

I use a bass drum mic right up against the cabinet and a DI.

[Rimskidog]

Your absolutely right that all of the above create a fix for the problem mentioned. It creates a small problem in itself though that you actually lose the benefit of some of the natural room sound created by the space. A better fix which sorts out the phase issue and keeps all the benefits of having a bit of space is the use of a Little Labs IBP (in-between-phase) tool. I use this method on bass all the time: perfect bass sounds every time!

[51m0n]

Now thats a cool little piece of kit, bet you've got more than, or have wanted to get another at some point!

Can that help fine tune room mics on a kit as well?

[Rimskidog]

[quote name='51m0n' post='801382' date='Apr 9 2010, 11:28 PM']Now thats a cool little piece of kit, bet you've got more than, or have wanted to get another at some point!

Can that help fine tune room mics on a kit as well?[/quote]

Yeah they are awesome. Great on drum kits, for double micing guitar cabs, all sorts of uses. I have a pair. :brow:

[cheddatom]

I can't figure out how they work?

[flyfisher]

Phase reversal won't solve the problem (unless the delay just happens to be the exact equivalent of a 180 degree phase difference), it's really just a simple mismatched delay issue and can be solved in various ways as descibed above.

Television studios have a similar thing with their cameras and they use delay lines to match the effective length of the cables from each camera to eliminate any problems when mixing/cutting between them.

A dual-beam oscilloscope is one way of checking the delays between two signals derived from the same source, but I accept this is not exactly a common piece of equipment in the average band or studio. But, as the original poster mentioned, if the delay can be calculated - and it manageably small - then it can also be easily compensated for using an extra length of cable in one of the sources.

[99ster]

These little [url="http://www.audient.com/audient/product/mico"]Audient dual channel pre-amps[/url] are useful for recording bass with DI/mic as they have sweepable Phase on one channel.

[Rimskidog]

[quote name='cheddatom' post='803548' date='Apr 12 2010, 11:37 AM']I can't figure out how they work?[/quote]

in short rather than just a phase reversal button which simply flips it 180, you can sweep through 360 degrees. This means that, for examply when you are double mic-ing something rather than look for the best position vis a vis the phase of the other mic you can simply put it where it gets the tone you want and then sync the phase up.

Edited April 17, 2010 by Rimskidog

[cheddatom]

ahhhh, thanks. Maybe I could make a box to sweep phase.

[shinhoman]

there is a feature in protools that corrects this... and its name has escaped me... argh!

i was using a protools 8 HD system though, it might not be on other versions

[Ian Savage]

[quote name='Wil' post='800791' date='Apr 9 2010, 01:01 PM']I think some mics have a phase reversal switch on them, not quite sure how this works, but I guess it's to combat this problem.[/quote]

The microphone phase reverse switch is a simple little thing that swaps the signal going to pin 2 of the XLR onto pin 3, and vice versa. Puts the output signal 180 degrees out-of-phase with the input signal, although as someone's already said unless your input signal to the microphone happens to be in the area of 180 degrees out of phase with the DI signal it's not a cure-all. The visual metering method's certainly the best way of doing things technically, although I just tend to get a lackey to move the mic around while the bassist's playing until it 'sounds best'.

[Rimskidog]

[quote name='shinhoman' post='818711' date='Apr 25 2010, 11:53 PM']there is a feature in protools that corrects this... and its name has escaped me... argh!

i was using a protools 8 HD system though, it might not be on other versions[/quote]

that'll be the cleverly named "phase reversal" button. There's one on pretty much every eq plugin.