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Compressing the Guitar Signal on the Mixer - Part 3

Compressing the Guitar Signal on the Mixer - Part 3 Brought to you by: guitar.com

Just Press Play Logo Gif 17809Be sure to read Part 2 before continuing onto this next segment.

This is a trick I use if I want major compression punch without smalling up the sound. This application can be used with almost any instrument as well, not just guitar.

The concept is to split off the guitar signal from one master module to two other mixer modules. One mixer module runs through a compressor and gets compressed big time causing a very small sound. The other mixer module does not use compression and is used as the body of the sound. The combination is the best of both worlds! Major punch and also major body!

 

 

OK, if the non-compressed sound is uneven in level it may need a taste of compression help. This is no problem and actually a good thing if the compressors are digital and the same model since digital processors cause a slight delay. More on the delay thing later.

The basic guitar/amp chain set up is different than others we have been using is past articles since we are going to split off the signal using a total of three mixer modules before routing to one or two compressors.

This set up is basically for a stand-alone analog or digital mixer and a stand-alone recorder. For hard disk mixer/recorder applications, simply adapt the following.

We start with our basic set up of using mixer module #9 for the miked guitar amp. We will route mixer module #9 to mixer module #10 and #11 to blend signals. The combined output of mixer module #10 and #11 will route to recorder track #7 .

 

Further Explanation of the Signal Path:

Mixer module #9 output routes to mixer module #10 and #11. Mixer module #10 may route to a compressor (if needed) and will route to recorder track #7. Mixer module #11 will route to a compressor (for major compression) and will route to recorder track #7.

The Routing Set Up In Full

Plug the guitar mic cable into mixer module #9 mic input. On module #9, to start, set the mic pre-amp trim to 20 dB. (If you have only one input gain trim pot, it 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 to start). Assign mixer module #9 to bus #7 (bus #7 routes to the recorder track we are using for the guitar). Make sure that module #9 is not sent through the monitor chain and is only routed to record track #7. Set recorder track #7 into input mode so we can monitor through the recorder. (In digital land, you may want to monitor the mic-input signal on module #9 BUT only do so if you notice a delay monitoring through the digital mixer and or recorder path. I will get into this subject in future articles). Bring up module #7 (recorder track return) about half way up on the fader throw. Bring up the studio control room monitor level up to a normal listening level. Ask the guitarist to play the part for the song. While the guitarist is playing, slowly bring up the fader on module #9 (guitar mic fader source) 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 to find the zero mark. Above Step #2 further adjustment: If you're 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. Above Step #2 further adjustment: If you're 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 and 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! But, there are no rules so this is a good time to slam level to see what digital distortion sounds like.

Regarding #8 and #9 above, if you are the guitarist and engineer, and if the amp is in a separate room (or closet or the like), you will be monitoring over the control room speakers. If there is no guitar amp isolation, meaning the amp is in the same room, you will be using headphones to monitor. In any case, if youll be 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.

 

Splitting the Signals to Modules #10 and #11

The levels are now set for a friendly gain structure so now its time to split off the signal to modules #10 and #11. The odds are good you will no longer be adjusting the level on mixer module #9, but will be simply using this module for the feed to mixer module #10 and #11.

Note on mixer module #9, we could have used the mic pre-amp output only for the split off point for the feed instead of the full module but many mixers do not allow that patch point. Further, we may want to use mixer module #9 for a master EQ if wanting to roll out an amp speaker cabinet bump or fix a suck out problem. With that in mind, here we go with the rest of the set up:

On mixer module #9, undo the send to bus #7. (Remember this module is no longer going directly to the recorder and is used for the feed to mixer modules #10 and #11.) Assign mixer module #10 and #11 to bus #7, to route the signals from modules #10 and #11 to recorder track #7. (Make sure the mixer monitor is all the way down at this point. You never want to do patching with the monitor volume up in case the patch is incorrect, possibly causing a feedback loop, etc.)

Using a mixer with built in compressors on each module: If you have unused busses, assign mixer module #9 to two unused busses. Patch one of the busses into mixer module #10 and the other into mixer module #11. If you have no extra busses, use the direct output on mixer module #9 and either patch into a mult or Y cord. In either case, patch into mixer modules #10 and #11 line inputs. Using outboard compressors and mixer modules with insert patch points: If you have unused busses, assign mixer module #9 to two unused busses. Patch one of the busses into mixer module #10 and the other into mixer module #11. If you have no extra busses, use the direct output on mixer module #9 and then either patch into a patch bay mult or Y cord. In either case, patch into mixer modules #10 and #11 line inputs. Now its time to patch in the compressor(s). If you want to slightly compress to even out some notes for the big sound path, patch in a compressor on mixer module #10 using the insert patch points. For the total squashed compressor sound, patch in the compressor on mixer module #11 using the insert patch points. Activate the insert if it has a switch to do so. (Note: Regarding the mixer module insert patch points, some mixers use a Tip Ring Sleeve (TRS) connector that is used for both the input and output insert patch point. If so, the other end of the patch cable will typically have two separate connectors to patch into the compressor input and output. Check your mixer manual for the insert wiring if you need to wire up such a cable.) Using outboard compressors and mixer modules without insert patch points: In this case, the compressor needs to be patched in before the mixer modules. If you have unused busses, assign mixer module #9 to two unused busses. If you have no extra busses, use the direct output on mixer module #9 and either patch into a patch bay mult or Y cord. If you want to slightly compress to even out some notes for the big sound path, patch one of the busses (or direct output multed-off signal) into a compressor input and patch the compressor output into mixer module #10. For the total squashed compressor sound, patch one of the busses (or direct output multed-off signal) into the compressor input and patch the compressor output into mixer module #11.

 

Time to EQ the Guitar Signal

Remember that the guitar signal is routed to mixer module #9. Mixer module #9 is not being monitored and instead is routing the signal to both mixer modules #10 and #11. Both mixer modules #10 and #11 are assigned to bus #7 which routes to recorder track #7. Recorder track #7 is set to input mode and the signal returns through mixer module #7, which is used for monitoring the guitar signal.

We may want to use mixer module #9 for a master EQ if needing to roll out an amp speaker cabinet bump or fix a suck out problem. The way to do that is to monitor only mixer module #10, meaning mute module #11 for now. If using a compressor on this module, set it to bypass mode for now. Adjust the EQ on module #9 to fix the bump or suck out. You may also want to EQ further if you like, dialing in the EQ to taste.

Now its time to work on the EQ for module #10. Un-mute module #10 and bring it up about half way on the fader throw. If you did not dial in the EQ in full on module #9, set it to taste on module #10. Now switch in the compressor. Since this leg of the sound is the big sound, you only want to catch a few peaks, so try a ratio setting of around 3 to 1 and a threshold that averages around 2 dB. Try a fairly fast attack and a fairly fast release. Now you may want to revisit the EQ settings to slightly tweak them. By the way, as usual, you want the EQ before the compressor. If you patched the compressor in using the mixer module insert patch point, and if there is a pre/post insert switch, set it to post to position the EQ before the compressor. Note that if this module does not need compression to slightly even out notes, there is no need to use the compressor. Now mute this mixer module since we do not want to hear this module when working with module #11.

Working with module #11: Un-mute module #11 and bring it up about half way on the fader throw. The first thing to do is work with the compressor settings. Start with the ratio of 10 to 1. Set the attack to fast and the release to near fast or fast. Set the threshold to average around 10 dB. If your compressor offers a hard knee option, use it. Refer to the compressor article for input and output level settings. Yes, the signal is squashed big time and should sound very small at this point. You may want to EQ the signal at this point but its best to wait until you blend in the big sounding mixer module.

 

Blending Mixer Modules #10 And #11

Now the fun starts! Make sure both mixer modules #10 and #11 are un-muted and pull both faders all the way down. As the guitarist plays the part, start by bringing mixer module #10 half way up (the big sound). Now start creeping in mixer module #11 fader. You will notice that a little of this signal goes along way, meaning probably about half of the fader throw distance compared to mixer module #10 will be plenty. OK, the trade off is body vs. squash. There are no rules as usual so, if you want mostly the squashed signal, great!

Now look at the meter on recorder track #7. Move both mixer module faders together in an equal level fashion and if using an analog recorder, set to average zero dB. If youre using a digital recorder, set the highest level to 4 dB.

You may now want to do some EQing on mixer module #11 (maybe on mixer module #10 as well). You may want to experiment with compressor settings for the squashed sound, etc. After doing so, check the levels on recorder track #7 as mentioned and adjust the levels as needed. You may also need to change the blend as you tweak stuff.

As mentioned, this concept works with many instruments. Try this with snare drums, kick drums, and tom toms. Its a great way to achieve aggressive sounds that retain body!

 

Phase Issues

In the future, I will do an article on phase issues and delays caused by digital processors in full but for now, there is one thing I need to explain: Digital processors cause a delay since they need to process the signal. Most digital processors in this era use 48kHz as their sample rate and the processor delay is typically 3 samples in the digital domain and typically around 27 samples if converting to analog. In the case of a processor that samples at 48 kHz, you would think that 3 or 27 samples is not a big deal. It is a big deal in our case of combining the same source sound. If you're only using one compressor for the full squash and it is a digital compressor, even if youre using a hard disk recorder/mixer combination, the 3 samples of delay will cause a comb filtering effect thinning out the sound to some degree. Like I said, Ill write more on this in full later but, for now, the workaround is as follows:

If the big sound on module #10 is not using a compressor and the squashed sound is using a digital compressor, or if both the big sound and the squashed sound are using compressors that are not of the exact same model, record on separate tracks. The fix is to time shift the late track forward in time after recording.

In this case, go back to The Routing Set Up In Full section (above) and make one change: Assign mixer module #11 to recorder track #8 (instead of recorder track #7). You now have the big sound on recorder track #7 and the squashed sound on recorder track #8. Set both levels on the recorder as mentioned, meaning an average of zero dB for analog and no more than 4 dB for digital recorders.

After recording, a track time shift will need to happen. With an analog recorder, there is a way to fix this when mixing the song. But, in this era of Pro Tools and the like, its best to transfer to such a format for the fix. If anyone cares to do in the future time-shifting with an analog recorder, email Guitar.com and I will do an article on that.

 

Quick Fixes for Comb Filtering

Ok, the best way to fix the comb-filtering problem is in the digital domain. If you're using a hard disk recorder/mixer system, look at the first sample attack of both waveforms on track #7 and #8. Move the later track back in time to match the first sample of the track with no delay. This will get rid of the comb-filtering problem and the combined sound will be very happy in phase land. I'll write much more on Comb Filtering in future columns.

OK, one more thing on phase for now. If you are hearing serious signal cancellation with near or equal level regarding mixer modules #10 and #11, no matter if recording on 1 or 2 tracks, one side has reversed polarity. If you're using an analog setup, and if your mixer has a phase switch, reverse either mixer module #10 or #11. That is a crap shoot, meaning you may reverse the wrong side, leading to the waveforms starting as negative waveforms. But its much better than being out of phase.

If using Pro Tools or the like, when looking at both waveforms at first attack, if one is going down (negative) and the other is going up (positive), reverse the waveform that is going down. Most all hard disk recording formats with screen waveform viewing have a mode to reverse (invert) the waveform shape.

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