Using 2 or More Mics for The Guitar Amp Speaker(s) - Part 3
This article is on using three or more mics on three separate speakers miking in front of the speaker(s). We will also cover using two mics on two amps in a stereo set up.
In this era, guitarists such my very good friend Steve Lukather, uses three separate amps and three separate speaker bottoms. One amp and speaker bottom for the non-effected sound and the other two amps and speaker bottoms for stereo effects. The non-effected speaker bottom is placed in the center and the other two speaker bottoms are placed left and right in relation of the non-effected speaker bottom.
You might think that using two amps and two speaker bottoms would be the way to go for a stereo signal since there would be no problem adjusting the blend on a stereo effect to allow the non-effected signal be equally split between both amps giving a phantom center. Yes, that works, BUT the drag is when using a loud distortion sound with an effect such as a stereo chorus, the guitar speakers are going through major movement dealing with the chorusing effect this causes the non-effected part of the signal to sound sloppy (for lack of a better word).
Regarding the two or three amp setup, I suggest reviewing the archived article on Miking The Guitar Amp (Part 3) since so much important physical set up information will not be covered here. Actually, the main mic set up we will use will be in that article as well. You may also want to review the article that mentions mic choices per application.
In this multiple mic series I have mentioned the following in italics. When using more than one mic in a close mic proximity amp miking situation, the key is to position the two (or more) mics the exact same distance from the speaker to eliminate comb filtering phase problems. Yes, even with careful placement, since the speaker is not flat (its kind of bowl shaped), its hard to measure the exact distance with one mic looking at the cone and the other looking about half way from the speaker center and side (typical positions). More on that as things unfold in this multiple mic article series.
In this era of hard disk recorders with many tracks available, if you're using such a format I highly recommend recording each mic to a separate track since this will allow fixing possible comb filtering problems after recording. This will also save time with mic positioning. (In this article, we will be recording to separate tracks.)
So how do you route the guitar to two or three separate amps? There are a few ways to do so and that needs a separate article. The way the pros do so is to use a pedal board setup that uses opamps to isolate the signal to each guitar amp. (Opamps are used for gain in mixers, recorders, etc and also used to isolate a signal, such as spitting off a guitar signal to two amps to get rid of a ground loop.) Bob Bradshaw is the guy that most pros use so look him up on the web for details.
Important! In the three-amp setup, as mentioned, the pedal board concept is typical. The effects are routed through the pedal board to specific amps. Its very important to set stereo effects to 100% wet that eliminates the dry (non-effected) signal out of the stereo chain, which is what we want. OK, in a situation where the effect is a stomp box that is plugged between the guitar output and pedal board input, all three amps will see the effect. That may make sense with a wah-wah. There are so many possibilities such as a mono effect on one side and so on.
Whether using the two amp and two speaker set up or three amps and at least three speakers, the article on using multiple mics on one or more speakers could easily be adapted in the following if wanting to get deep. Let's keep things simple and use two mics on two speakers or three mics on three speakers.
For the two mic set up (stereo effects with phantom center), we want the mics to be positioned the same to avoid possible comb filtering problems. For the three mic set up, possible comb filtering problems will mostly not be in play. This is because the non-effected signal (center speaker bottom) and the stereo effects (left and right speaker bottoms) are all doing something different in the time spectrum. For example, let's say that the stereo effect is a reverb. In this era, reverb programs use reflections and delays that are bouncing around in time all over the place in the stereo spectrum. Even if you reversed the phase on one side, in most cases, you would not hear a difference.
OK, after saying that, you might have set a delay to the exact time on both sides OR you might use all three amps for a dry non-effected sound at some point in the performance. As to play it safe, we will position all mics using the same distance from the speakers.
At this point, its most important to refer to the article on Miking the Guitar Amp (Part 3) for details. The following is from that article but best to read it full. We will use a guitar amp speaker cabinet with one speaker to start. If the speaker bottom has grill cloth and you do not want to remove, or if you cant see the center of the speaker clearly, use a flashlight. Look at the speaker and notice the dust cover in the center. Point the mic at exact center and then move the mic left without changing the height of the plane until you are about an inch left from the edge of the center dust cover. Now place the mic about once inch back from the grill cloth. If you have no grill cloth, imagine where it would be in front of the speaker. Now position the mic capsule at a 20 degree angle pointing towards the center of the speaker.
It's best to read the article in full for stuff like if using speaker bottoms with more than one speaker, you need to find the best sounding speaker. As always, do that test after setting up basic levels on the mixer!!! This will not be mentioned again since this has become that standard way to work in this article series.
Using two amps and two speakers for the stereo effects and a phantom center for the non-affected sound. You may be using a stereo amp such as a Roland Chorus that has two speakers. In any case, its best to mic both amp speakers exactly the same way as explained in the Miking The Guitar Amp article.
In this case, you would want to record to two separate tracks. See article #16 for full set up and routing details. Also, check article #17 for comb filtering issues. The only difference in the sonic path is you would want to pan both recorder track returns to full left/right or somewhere in the panning stereo spectrum. Best to decide which pan positions you will use when mixing the song since when balancing the phantom center dry (non-effected) sound; the phantom center may build up, causing the effects to be distant sounding in comparison.
Signal Path For Three Mics to Three Recorder Tracks
Note this is different that the routing we have been using in previous articles.
Important! Set up the effect patch that will be used for the song. If more than one patch will be used, when setting levels on the record mixer, start with the patch that has the most level.
(As usual, if you are the guitarist and engineer, and if the amp is in a separate room or closet, you will be monitoring over the control room speakers. If you have no guitar amp isolation, meaning the amp is in the same room, you will be using headphones to monitor. In any case, if you're playing chords for the guitar part, play all the open strings when adjusting the level with your other hand. If you'll be playing single notes for the part, simply play one string for now, such as the D or G string, and adjust the level with the other hand.)
For our example, we are recording the guitar on recorder tracks #6, #7 and #8 and using mixer modules #9, #10 and #11 for the three guitar mic inputs. Lets use mixer module #9 for the mic for the left effect amp speaker bottom. Let's use mixer module #10 for the mic for the dry (non-effected) center amp speaker bottom. Let's use mixer module #11 for the mic for right effect amp speaker bottom. If you're using a digital recorder with a built in mixer, simply adapt with the same layout.
1. Plug the mic cable for the left effect amp speaker bottom into mixer module #9s mic input.
2. Plug the mic cable for the dry (non-effected) center amp speaker bottom into mixer module #10s mic input.
3. Plug the mic cable for the right effect amp speaker bottom into mixer module #11s mic input.
4. On mixer modules #9, 10 and #11, to start, set the mic pre amp trim to 20 dB. (If you have only one input gain trim pot per mixer module, that is used for both source line input gain and mic input gain. If using a computer hard disk recorder with outboard analog to digital inputs, use the same setting on the input level control as to start).
5. Assign mixer module #9 to bus #6 (bus #6 routes to the recorder track we are using for the left effect amp speaker bottom). Note that if mixer module #9 has a direct output, instead of using bus #6, patch the direct output into recorder track #6s input. Make sure that module #9 is not sent through the monitor chain and is only routed (bussed) or patched directly into record track #6. Mute this module for now.
6. Assign mixer module #10 to bus #7 (bus #7 routes to the recorder track we are using for the dry (non-effected) amp speaker bottom). Note that if mixer module #10 has a direct output, instead of using bus #7, patch the direct output into recorder track #7s input. Make sure that module #10 is not sent through the monitor chain and is only routed (bussed) or patched directly into record track #7. Mute this module for now.
7. Assign mixer module #11 to bus #8 (bus #8 routes to the recorder track we are using for the right effect amp speaker bottom). Note that if mixer module #11 has a direct output, instead of using bus #8, patch the direct output into recorder track #8s input. Make sure that module #11 is not sent through the monitor chain and is only routed (bussed) or patched directly into record track #8. Mute this module for now.
8. Pan mixer module #6 full left, pan mixer module #7 to center, and pan mixer module #8 full right. Yes, you can change it later but its best to start here.
9. Set recorder tracks #6, #7 and #8 into input mode so we can monitor the guitar signal through the recorder, which routes to mixer modules #6, #7and #8. (In digital land, you may want to monitor the mic-input signal on modules #9, #10 and #11 BUT only do so if you notice a delay when monitoring through the digital mixer and or recorder path. I will get into this subject in future articles. Anyway, if you're monitoring this way, pan mixer module #9 full left, pan mixer module #10 to center, and pan mixer module #11 full right.)
10. Bring up the studio control room monitor level up to a normal listening level.
11. Mixer module #10 level settings: (We are starting with the non-effect channel first) Bring up module #7 (recorder track return) about half way up on the fader throw. Ask the guitarist to play the part for the song. While the guitarist is playing, un-mute mixer module #10 and slowly bring up the fader to zero (unity gain). This level setting is typically around 3/4ths up on the fader throw Look at the etching next to the fader as to find the zero mark.
11a. If using an analog mixer and recorder (hardly used these days) adjust the mic pre amp trim level on the mixer to average zero dB on the recorder track meter for now. For now, mute mixer module #10.
11b. If using a digital recorder format, adjust the mic pre amp trim level to -4 dB on the recorder track meter for now (-4 dB is safe in case the guitarist players louder when recording the odds are good that will happen!) Always remember that going into the red (past zero) on a digital format meter will definitely clip the A to D converter (analog to digital converter) which is not advisable!!! Digital distortion sounds terrible!!! Yea, no rules so this is a good time to slam level as to see what digital distortion sounds like. For now, mute mixer module #10.
12. Mixer module #9 level settings: Bring up module #6 (recorder track return) about half way up on the fader throw. Ask the guitarist to play the part for the song. While the guitarist is playing, un-mute mixer module #9 and slowly bring up the fader to zero (unity gain).
12a. If using an analog mixer and recorder adjust the mic pre amp trim level on the mixer to average zero dB on the recorder track meter for now. For now, mute mixer module #9.
12b. If using a digital recorder format, adjust the mic pre amp trim level to -4 dB on the recorder track meter for now. Dont distort. For now, mute mixer module #9.
13. Mixer module #11 level settings: Bring up module #8 (recorder track return) about half way up on the fader throw. Ask the guitarist to play the part for the song. While the guitarist is playing, un-mute mixer module #10 and slowly bring up the fader to zero (unity gain).
13a. If using an analog mixer and recorder adjust the mic pre amp trim level on the mixer to average zero dB on the recorder track meter for now. For now, mute mixer module #11.
13b. If youre using a digital recorder format, adjust the mic pre amp trim level to -4 dB on the recorder track meter for now.
14. Now listen to all three channels and set a basic monitor blend. More on the blend down below.
EQ Settings : EQ the three mics separately. Refer to the articles on EQ per the application (Parts 4 through 9). Mute mixer modules #9 and #11 since we will EQ the dry (not effected) sound first on mixer module #10. EQ the signal on mixer module #10 to taste. When you are happy with the EQ settings, mute mixer module #10 and un-mute mixer module #9. EQ to taste. If the stereo effect is a chorus, reverb or any effect that is a true stereo effect, simply copy the EQ settings on mixer module #9 to #11. Now un-mute mixer module #11 and see if the EQ sounds the same as mixer module #9 signal. If you're using the same mic model on both, the sound should be the same or very close. OK, the effects may be set up to have different internal EQ on both sides. Man, as usual, there are no rules so if you want the stereo effects to sound different in EQ land, great!
In all of the following steps, you may want to tweak the EQ on mixer modules #9, #10 and #11.
The Blend in full: Keep in mind that we are recording to three separate recorder tracks so the blend is a simple monitor blend that is not permanent. In any case, you should set a good monitor blend between mixer modules #6, #7 and #8. In most cases, you will feature the dry (non-effected) signal and blend in the panned effects to taste. Note that we have panned mixer modules #6 and 8 (the stereo effects) to full left and right. You might try panning in a taste if the overall signal is too wide (try 9 oclock for the left side and 3 oclock for the right side). Typically, you would pan in the same amount but you can make that decision when mixing. Note: If you're using the 5.1 format for monitoring and mixing, you have so many pan possibilities!
To set the blend: pull down mixer module #6, #7 and #8 faders to the bottom of their throws. Make sure both mixer modules #9, #10 and #11 are un-muted. While the guitarist is playing (as always when dealing with electronic settings), slowly bring up both faders and experiment with different level settings to achieve a good blend. When needing to change the overall guitar monitor level when listening to the full band, simply move mixer modules #6, #7 and #8 faders together keeping the same relative levels. If you have mixer automation, set these faders to group mode so one fader controls the other two, or use a separate group fader for all three faders.
Adding the Compressor: Refer to the articles on compressors (Parts 10 through 13). In this case, you will need three compressors. You might want to use a stereo compressor on the left and right effects. In any case, start with the dry (non-effected) sound on mixer module #10. Then work with mixer modules #9 and #11 as a team IF the effects are stereo. If not, work with each side one at a time. Note that if the effect is reverb only, compression may not be needed.
Now redo the monitor mix blend.
Important! I almost forgot to mention: When dealing with the blend, its best to do a quick check for possible phase problems. First bypass the guitar effects (leave the effects switched in on the pedal board and use the bypass switch on each effect active). If using EQ on the mixer or compressors, bypass them for now. Pan all three mixer modules to center (the dry sound is already panned to center). If the signal happens to cancel out with the levels near or the same, there is an electronic phase problem. The problem may be caused from the one of the three speakers one may be wired reverse phase or it may be a wiring path problem in the guitar pedal board chain. In any case, this is easy to discover.
Simply listen to all of the amps in the room (not over the studio monitor speakers). With the effects switched out, put each amp in standby mode one at a time until finding the problem. Swap out the speaker cable WITH THE AMP OFF! If thats not the fix, swap out the cables that are active in the path. That will depend upon how the set up is wired.
If that's not the fix, the phase problem is somewhere in one of the three paths starting with a mic through the mixer/recorder path. The odds are good a cable in the chain is wired incorrectly. If you are using a hard disk recorder format, record a few bars and look at the initial waveform attack on all three tracks. If you see one waveform dipping down at initial attack, that is the path that has incorrect wiring somewhere in the chain. You should find out where the problem is using the following concept.
Mute the mixer module that is showing the reverse phase. Also mute the studio monitor speakers. After each of the following changes, un-mute both and listen to the three mic tracks to see if the cancellation goes away.
1. First swap out the mic.
2. If that's not the fix, swap out the mic cable.
3. If that's not the fix, plug the mic into another mixer module and duplicate the set up on the mixer module to the recorder.
4. If that's not the fix, route the mixer module to another recorder track.
By now you should have found the problem so use a piece of red tape on the incorrectly wired component as to let you know a tech needs to fix the wiring.
Without a hard disk recorder that can view waveforms, you do not know which of the three tracks in the chain is phase reversed. The first thing to do is to mute one recorder return mixer module at a time. Mute mixer module #6. Did the phase problem go away? If so, that is the path with the problem. If not, mute and un-mute mixer module #7 and mute mixer module #8. You get the drift. Try all combinations until finding the path with the problem.
After finding the path with the problem, simply perform the above 4 steps on the mixer signal path and you will find the problem. Again use a piece of red tape on the incorrectly wired component as to let you know a tech needs to fix the wiring.