2 mics, recorded tracks offset.

[davidcatpi]

Hi all. A noob here.

I'm recording a guitar riff with two different mic's at the same time. SM57 and MXL R77 (ribbon) at different distances from the speaker. (dynamic at dust cap/cone edge, ribbon 1 feet away, slightly off-center), into separated tracks.

Having a close look at the recorded waves in Cubase, track 2 (ribbon, farthest away from the speaker) has an offset which increases If I move the mic even farther away from the amp which I think it's how it is supposed to be.

Since my intention is to shape a dead (no room ambience) guitar sound, is eliminating the offset by moving second track back to where the waves become coherent (very high precision intended) just a stupid idea or not that much really? I know I'm supposed to go by my "feelings" here, and let the sound decide but maybe there's a bit of science behind this that can guide me some.

Thx!

 

[bouldersoundguy]

Experiment and use your ears to decide.

I often use two mics, one close and one far, on a guitar cabinet. Normally I do slide the far one so the direct sound (as opposed to the reflected sound) lines up with the close mic's signal. Although I rough it in using 1ms/foot (approximating the speed of sound) I do the final alignment by ear.

If you pan the two mics apart they will have better mono compatibility if they're time aligned.

 

[ashcat_lt]

Nudging the track will tend to shorten the early reflections and remove some of the "roominess". Leaving it offset can cause comb filtering issues sometimes.

The big question becomes: are you using the further mic just for "air" or ambience, or are you trying to mix the direct sound of the two mics? If you're mixing them in such a way that the direct sound on both tracks is roughly equal, that's where you'll have the "phase issues" and nudging will help that. This is where the often misunderstood "3 to 1 rule" comes in. I prefer to call it the "(at least) 9db Rule (of thumb)". It says that if the two direct sounds are mixed in such a way that one is at least 9db louder than the other, the comb filtering will not be noticeable.

Of course, the really big question is: how does it sound? Even if there is severe comb filtering going on, if it fits the mix and sounds good to you, then you're doing it right!

 

[miroslav]

Since my intention is to shape a dead (no room ambience) guitar sound, is eliminating the offset by moving second track back to where the waves become coherent (very high precision intended) just a stupid idea or not that much really? !

Just time-aligning the two tracks in the DAW will not remove the room ambience...especially with the ribbon which is further away and picking up more room. With two mics at different distances from the source, you are actually creating a "delay" between them, in addition to the room ambiance which is always there.
The close mic will just pic up less of the room...and time-aligning the two tracks will only remove that "delay" you created.

If you want a dead guitar sounds, try placing a "tent" over the amp, and both mics. You can create a tent with some chairs and a couple of layers of thick blankets. Then you can decide how much you want to time-align the two tracks or not...but the room ambiance will be effectively removed from both mics.

Here's some pics of how I do a "tent"....though lately I've gone without one on most guitar tracks, prefering to have some room life in them, but that's a personal choice.

 

[davidcatpi]

Hey thanks for the quick responses!

Yes, a direct sound is what I'm aiming for here, so aligning both tracks is not a bad idea after all. No "roominess" needed mainly because the room I'm using has no treatment at all, is medium sized and I need to keep volume kinda low.
My logic here was to use SM57's grit and bite, apply high/low pass filters and add a bit of the ribbon's warmer, low-mid tone, so while experimenting a did notice that It just sounds better if I keep the secondary track (ribbon in this case) at about 60-70% and primary mic at 100%. Having both at equal levels left the tone with no character at all.

I guess that, in the case of needing to capture ambience sound, I would use a condenser (from what've heard) and leave the offset just as it is.

Indeed you are right, the sound picked by the MXL should have some ambience into it. I like the tent, might give it a try! I paid a look on how to build an isolation box a few months ago but never really started it.

 

[bouldersoundguy]

Sufficient difference in level (6dB or more) will reduce the effects of interference (that cause "comb filtering"), but the 3:1 distance rule of thumb doesn't apply to this situation. It applies when you want a sound in one mic but not the other, or when there are two sources and you want a mic to pick up only one of them. You use 3:1 when you want to isolate mics and sources, not when you're mixing two mics on one source.

 

[davidcatpi]

I made a couple of examples, it's a random riff where you will hear the SM57 and the MXL (at slighty lower volume), first 5+/- seconds have the unmodified, offset tracks and then switches to the same recording with the tracks aligned.

SM57/MXL 1 FEET

SM57/MXL 2 FEET


One clip has a much stronger effect, and I perceive some scooped out mids on the unaligned tone, maybe suitable for metal and such, aligned tracks sound warmer and louder.

Theres a delay effect along the signal so to provide some "room". No pass filters nor EQs, just raw recording.

I also notice that perceived distortion is much higher that what my ear hears, the amp's gain is set at 40%, and there's a clean ts808 boosting the signal.

So yeah, It's just matter of going with what you like/need.

 

[ashcat_lt]

Sufficient difference in level (6dB or more) will reduce the effects of interference (that cause "comb filtering"), but the 3:1 distance rule of thumb doesn't apply to this situation. It applies when you want a sound in one mic but not the other, or when there are two sources and you want a mic to pick up only one of them. You use 3:1 when you want to isolate mics and sources, not when you're mixing two mics on one source.

Nope, it's for avoiding comb filter effects in any situation where one source might be picked up in 2 mics, or otherwise mixed with a delayed version of itself. Distance is one way to achieve that 9db "threshold of acceptability." Polar pattern can be another. Just turning down the fader on one of the tracks accomplishes the same thing. Yes, it's important when you're mixing two sources "separately", but if one considers the direct amplifier sound and the ambience as separate sources...

 

[ashcat_lt]

Hey thanks for the quick responses!

Yes, a direct sound is what I'm aiming for here, so aligning both tracks is not a bad idea after all. No "roominess" needed mainly because the room I'm using has no treatment at all, is medium sized and I need to keep volume kinda low.
My logic here was to use SM57's grit and bite, apply high/low pass filters and add a bit of the ribbon's warmer, low-mid tone, so while experimenting a did notice that It just sounds better if I keep the secondary track (ribbon in this case) at about 60-70% and primary mic at 100%. Having both at equal levels left the tone with no character at all.

I guess that, in the case of needing to capture ambience sound, I would use a condenser (from what've heard) and leave the offset just as it is.

Indeed you are right, the sound picked by the MXL should have some ambience into it. I like the tent, might give it a try! I paid a look on how to build an isolation box a few months ago but never really started it.

The filters add a couple new wrinkles to the question. Firstly, unless you're using linear phase filters, they will add their own frequency dependent delay. But there can only be noticeable interference where the two signals are close in level (that 9db thing again).

If you were crossing them over with an HPF on one and an LPF on the other, you'd really only have a chance for weirdness (comb filter wise) in the region around the cutoff frequency. Everywhere else will be dominated by one signal or another. In practice you'll either have a bit of a bump or a dip somewhere close to the cutoff frequency, or you wont have any noticeable effect. It's pretty simple math really, but there are enough variables involved to where it's essentially just luck. It's exactly the reason that you should have listened very carefully when placing the mics (with all the processing in place), and why you should just use your ears to tell if nudging is necessary or harmful. Physics makes the calculations instantaneously and our ears are the best instruments on earth for measuring the effects.

 

[bouldersoundguy]

Nope, it's for avoiding comb filter effects in any situation where one source might be picked up in 2 mics, or otherwise mixed with a delayed version of itself. Distance is one way to achieve that 9db "threshold of acceptability." Polar pattern can be another. Just turning down the fader on one of the tracks accomplishes the same thing. Yes, it's important when you're mixing two sources "separately", but if one considers the direct amplifier sound and the ambience as separate sources...

If you're treating the far mic as ambient-only then the ratio is dependent on variables such as the room size and reverberation, amp placement etc. "Critical distance" might be the more applicable term.

When both mics are intended to pick up the same source 3:1 doesn't apply since mix settings will overrule level differences between the mics.

 

[ashcat_lt]

If you're treating the far mic as ambient-only then the ratio is dependent on variables such as the room size and reverberation, amp placement etc. "Critical distance" might be the more applicable term.

I suppose that depends just how much ambience you want. Maybe a foot from the amp is just right. You do need to at least keep the "rule" in mind.

When both mics are intended to pick up the same source 3:1 doesn't apply since mix settings will overrule level differences between the mics.

We're sort of not arguing this point really. It could also be said that 3:1 doesn't apply in the case of micing two sources with directional microphones, since careful use of polar response can "overrule" the distance thing the same way.

It's exactly why I talk about 9db much more often than 3:1. 9db happens to be just a little less than a 3:1 ratio in voltage, but the 3:1 thing implies distance to most folks. It ain't the distance that matters, though, but the volume ratio.

 

[mixsit]

...It's exactly why I talk about 9db much more often than 3:1. 9db happens to be just a little less than a 3:1 ratio in voltage, but the 3:1 thing implies distance to most folks. It ain't the distance that matters, though, but the volume ratio.

Not a bad idea at all- or call it the 3:1 9dB Attenuation rule. Anything that directs away from the implications of 'phase alignment.
Yep.. It's still there Sweetwater...
What is "3:1 Rule of Microphone Placement"?

 

[bouldersoundguy]

Not a bad idea at all- or call it the 3:1 9dB Attenuation rule. Anything that directs away from the implications of 'phase alignment.
Yep.. It's still there Sweetwater...
What is "3:1 Rule of Microphone Placement"?

The first paragraph is just plain wrong. When micing one source there's no ideal ratio, you do whatever sounds right for the situation.

The second paragraph is the usual description referring to the distance between the mics, but it's the ratio of the two source-to-mic distances that matters. The mic-to-mic distance isn't the important measurement. It gets the job done but it's not technically correct.

 

[bouldersoundguy]

I suppose that depends just how much ambience you want. Maybe a foot from the amp is just right. You do need to at least keep the "rule" in mind.

Once it depends on variables it's not really a rule any more. You just have to try things and listen.

We're sort of not arguing this point really. It could also be said that 3:1 doesn't apply in the case of micing two sources with directional microphones, since careful use of polar response can "overrule" the distance thing the same way.

I would say polar patterns can add to the separation you get from 3:1 rather than overrule it.

It's exactly why I talk about 9db much more often than 3:1. 9db happens to be just a little less than a 3:1 ratio in voltage, but the 3:1 thing implies distance to most folks. It ain't the distance that matters, though, but the volume ratio.

You can't look at mics and sources and see 9dB. You can look at the positioning of mics and sources and easily estimate 3:1 distance ratios.

By the way, isn't SPL a power measurement? So 3:1 would be 4.5dB, right?

 

[mixsit]

The first paragraph is just plain wrong. When micing one source there's no ideal ratio, you do whatever sounds right for the situation.

The second paragraph is the usual description referring to the distance between the mics, but it's the ratio of the two source-to-mic distances that matters. The mic-to-mic distance isn't the important measurement. It gets the job done but it's not technically correct.

It's been up for years -I even e-mailed them once (yeah what ever
So, what'a ya suppose?
a) they actually don't know
b) 'No it/that is just a matter of your opinion.'

There's the 'don't give a rat's ass' option too 'I spose

 

[miroslav]

The first paragraph is just plain wrong. When micing one source there's no ideal ratio, you do whatever sounds right for the situation.

While I would go with the "whatever sounds right" approach....there is something to the 3:1 distance between mic1 and source and mic2 to mic 1.

This video covers it...and the end of the video has a demo of what happens to the sound when you are in that "less than" 3:1 area with the second mic.

 

[ashcat_lt]

Once it depends on variables it's not really a rule any more. You just have to try things and listen.

Yep, that's always the best answer. OP asked for "science", so I went there.

I would say polar patterns can add to the separation you get from 3:1 rather than overrule it.

But it can also buy you separation when you can't get the full distance for some reason. It's relative volume that matters.

You can't look at mics and sources and see 9dB. You can look at the positioning of mics and sources and easily estimate 3:1 distance ratios.

Quite true. Only works if the mics have the same sensitivity and gain settings, of course. It's the relative volume that matters.

By the way, isn't SPL a power measurement? So 3:1 would be 4.5dB, right?

Weren't you the one who mention the inverse square law?

 

[bouldersoundguy]

While I would go with the "whatever sounds right" approach....there is something to the 3:1 distance between mic1 and source and mic2 to mic 1.

It's the source-to-mic distances that actually matter. The mic-to-mic distance is incidental but close enough to work in a multi mic/multi source situation.

This video covers it...and the end of the video has a demo of what happens to the sound when you are in that "less than" 3:1 area with the second mic.

Note that he specifies multiple mics on multiple singers for the first part of the demo.

There are two things going on in that part at the end. The phase effects themselves are not due to the ratio of the distances but the absolute time arrival differences. The same phase effects would occur if the source were a mile rather than an inch. How audible the phase effects are does depend on distance ratios, but if you are recording a single source with two mics you will probably compensate for the level difference with gain. If you're going to leave a mic low enough not to sound bad with the other mic why bother with the second mic in the first place?

 

[bouldersoundguy]

But it can also buy you separation when you can't get the full distance for some reason. It's relative volume that matters.

Yep, or add to the separation you get with 3:1.

Quite true. Only works if the mics have the same sensitivity and gain settings, of course. It's the relative volume that matters.

Sensitivity differences between mics is irrelevant because levels will be controlled by gain settings. Gain is set as needed by the given source, mic and placement. If you placement is good, makes use of distance and polar pattern to get sufficient separation, then you can set gain and set mix levels without being constrained by bleed.

Relative volume matters but when dealing with multiple sources/multiple mics it's distance and polar pattern that get you there.

 

[miroslav]

It's the source-to-mic distances that actually matter.

Well either...because if you're distance from mic2 to mic1 is increased three fold the distance of mic1 to source....then the distance of mic2 to source is automatically increased proportionally, and ends up being 4x what mic1 is to source.

The part in the end of the video shows how "phasey" the combination of both mics sounds when mic2 is less than 3:1 of mic1...there's just that point in the distance/time arrival where the phase issue is not as much of an issue.

Anyway...I have not to this day ever bothered to take out a ruler to measure when placing mics/mulitple mics....it's more of a by-eye and then what-sounds-best technique.