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Compressing the Guitar Signal on the Mixer - Part 1

Compressing the Guitar Signal on the Mixer - Part 1 Brought to you by: guitar.com

Just Press Play Logo Gif 13406Around 90 percent of the time, we want to compress the guitar, and for a few reasons. We typically use the compressor to kind of even up note or chord levels, and to add punch. Punch in this case has nothing to do with punching in on the recorder. Instead, it is energy applied to the attack of a signal to create excitement. For those of you who do not know how a compressor or a limiter works, here we go:

A compressor (or limiter) controls the amount of level reduction that passes through the compressor, set by the compressor threshold point. The amount of level that passes beyond the threshold is also affected by the ratio control. Lets start with a compressor first. For example, lets say that the threshold is set to 0 dB. Lets say that the ratio control is set to 2 to 1. For every 2 dB the compressor sees in level above the threshold setting, it will pass only 1 dB of signal. If the ratio is set to 4 to 1, for every 4 dB of level the compressor sees above the threshold setting, it will pass only 1 dB of signal.

A limiter is more extreme, meaning its typical use is to totally brick wall the sound all input signal hitting the threshold level equals the same output level. Many limiters allow threshold ratios that are adjustable but, to make things simple, we will assume the limiter is used to totally brick wall the signal.

Limiters are typically used for radio and TV audio and are not typically used for instruments. But hey, there are no rules so, if you like the limiting mode (when offered in a compressor or when using a stand alone limiter), and it works for the sonic application, use it. The following relates to both limiters and compressors but we will be dealing with compressor settings for the most part.

 

Setting Compressor Thresholds

Back to compressors. For clean guitar playing such as Pop or R&B rhythm and lead, the note(s) attack creates a major transient (also known as a spike). For example, if looking at a waveform on a screen, the attack will have an amplitude way above the rest of the waveform level. When the transient goes beyond the compressor threshold setting, and if its a level of at least 5 dB past threshold, the compressor (or limiter) squashes it hard, causing a very strong hard hitting attack this is known in the industry as punch.

The higher the ratio setting and the more input level added past the compressor threshold, the more punch. There are other factors such as the attack and release time set on the compressor. A fast attack time makes the sound more punchy while a slower attack time allows more of the non-compressed signal to pass through before the threshold is activated, equaling less punch. Yes, a spike will pass through the threshold if the compressor is set to a slow attack setting.

With guitar distortion we know that the amps distortion heavily compresses the signal within its electronics. Even so, as mentioned above, there can be uneven notes, especially when playing low string power 5ths, caused by the speaker cabinet creating build-ups and suck outs. This is especially true in low to low mid-range frequency areas. If the levels are uneven you should be able to smooth out the frequency problems by carefully EQing (as described in several of the previous columns in this series) before compressing. If not, try compressing more than usual.

Regarding solo line playing: Solos typically provide only little frequency bumps or suck out problems, and the compressor will surely take care of those. Solo line playing loves compression to add some punch. Note that even if the guitarist is using a compressor as an effect from the guitar through the amp chain, further compression within the recorder mixer chain is common to smooth out the speaker cabinets small bumps and suck outs.

 

Possible Adjustable Parameters for the Compressor (or Limiter)

- Threshold level (may be the input level as well) - Input level - Output level - Ratio setting - Attack time - Release time - Compressor or limiter mode - Stereo mode (if using a two-channel unit, or two mono units that allow the option) - Side chain mode

Before we get into patching in the compressor (or limiter), here are some common settings for the compressor for various applications. Refer to this information after patching into the mixer/recorder path.

 

Pop or R&B Rhythm and Lead:

- Threshold level (may be the input level as well): For rhythm, typically an average of 3 dB over the threshold setting with a peak around 6 dB. For a clean lead sound wanting to be aggressive in punch land, you may want an average of 6 dB over the threshold setting with a peak around 10 dB. - Input level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the input level if the level does not match, i.e. a 10 dB compressor seeing +4 dB level input from the mixer. Level matching will be explained in the next article. - Output level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the output level if the gain does not match. Level matching will be explained in the next article. - Ratio setting: 4 to 1. Note that the higher the ratio, the smaller the sound since more squash is in play. - Attack time: Medium to fast. The faster the setting, the more snap/punch. - Release time: Medium to fast. The key here is if playing many notes quickly. A fast release will allow each attack to be attacked by the compressor. The slower the release time, the more time it takes the compressor to recover so all notes played before recovery will sound lower in level. - Compressor or limiter mode: I always set to compress, but there are no rules as usual. - Stereo mode: (if using a two-channel unit): Typically not needed. More on this in the next article. - Side chain mode: Typically not needed. More on this in the next article.

 

Distortion Guitar:

- Threshold level (may be the input level as well): Typically an average of 2 dB over the threshold setting with a peak of 4 dB. - Input level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the input level if the gain does not match, i.e. a 10 dB compressor seeing a +4 dB level input from the mixer. Level matching will be explained in the next article. - Output level: Set to unity gain (zero dB). Output level: Set to unity gain (zero dB) if using an outboard compressor, you may need to increase or decrease the output level if the gain does not match. Level matching will be explained in the next article. - Ratio setting: 3 to 1. Note that the higher the ratio, the smaller the sound. - Attack time: Medium to fast. The faster the setting, the more snap/punch. - Release time: Medium to fast. The key here is, if youre playing many notes quickly, a fast release will allow each attack to be attacked by the compressor. The slower the release time, the more time it takes the compressor to recover so all notes played before recovery will sound lower in level. - Compressor or limiter mode: I always set to compress. - Stereo mode: (if using a two-channel unit): Typically not needed. More on this in the next article. - Side chain mode: Typically not needed. More on this in the next article.

 

Crunch Guitar: This area can use more compression since part of the sound is clean.

- Threshold level (may be the input level as well): Typically an average of 3 dB over the threshold setting with a peak of 6 dB. - Input level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the input level if the level does not match, i.e. a 10 dB compressor seeing a +4 dB level input from the mixer. Level matching will be explained in the next article. - Output level: Set to unity gain (zero dB). Output level: Set to unity gain (zero dB) if using an outboard compressor, you may need to increase or decrease the output level if the level does not match. Level matching will be explained in the next article. - Ratio setting: 3 to 1. Note that the higher the ratio, the smaller the sound. - Attack time: Medium to fast. The faster the setting, the more snap/punch. - Release time: Medium to fast. The key here is, if youre playing many notes quickly, a fast release will allow each attack to be attacked by the compressor. The slower the release time, the more time it takes the compressor to recover so all notes played before recovery will sound lower in level. - Compressor or limiter mode: I always set to compress. - Stereo mode: (if using a two-channel unit): Typically not needed. More on this in the next article. - Side chain mode: Typically not needed. More on this in the next article.

Jazz Guitar and Chord Melody Guitar: The following compression suggestions are for straight-ahead jazz guitar. If the style being played is closer to a smooth jazz style, its best to cross-reference with the compression suggestions Pop or R&B Rhythm and Lead.

For straight-ahead jazz guitar, watch out here since compressors mess with dynamics and make the sound small. As I have mentioned before, jazz guitarists dislike an engineer messing with their dynamics and thinning out their sound. I rarely use compression for this application but, there are no rules friends. The key here is a medium attack setting to let the transient pass through.

- Threshold level (may be the input level as well): Typically an average of 2 dB over the threshold setting with a peak of 4 dB. - Input level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the input level if the level does not match, i.e. a 10 dB compressor seeing a +4 dB level input from the mixer. Level matching will be explained in the next article. - Output level: Set to unity gain (zero dB). Output level: Set to unity gain (zero dB). If using an outboard compressor, you may need to increase or decrease the output level if the level does not match. Level matching will be explained in the next article. - Ratio setting: 2 to 1. Note that the higher the ratio, the smaller the sound. - Attack time: Medium. - Release time: Fast. The key here is, if youre playing many notes quickly, a fast release will allow each attack to be attacked by the compressor. The slower the release time, the more time it takes the compressor to recover so all notes played before recovery will sound lower in level. - Compressor or limiter mode: I always set to compress. - Stereo mode: (if using a two-channel unit): Typically not needed. More on this in the next article. - Side chain mode: Typically not needed. More on this in the next article.

Refer to the above after setting up the following signal path.

As a reminder and to avoid having to read past articles, here is the mixer set up example that Ive used throughout this series: For our example, we are recording the guitar on recorder track #7 and using mixer module #9 for the guitar mic input. If you're using a digital recorder with a built-in mixer, simply adapt with the same layout.

- 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, used for both source line input gain and mic input gain. If you're 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 (buss #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) to 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. - If using an analog recorder (yes, hardly used these days, but some artists and producers swear by them) adjust the mic pre-amp trim level to average zero dB on the recorder track meter for now. - If you're using a digital recorder format, adjust the trim level to 6 dB on the recorder track meter for now. Always remember that going into the red (zero) on a digital machine peak meter will definitely clip the A to D converter (analog to digital converter) which is not advisable digital distortion sounds terrible! But then, there are no rules, so this would be a good time to slam the level to see what digital distortion sounds like.

Regarding #7 above, if you are the guitarist and engineer, if the amp is in a separate room (or closet or some kind of seriously baffled enclosure), you will be monitoring over the control room speakers. If you have no guitar amp isolation, meaning the amp is in the same room (and only partially baffled), you will be using headphones to monitor. In any case, if youre playing chords for the guitar part, play all the open strings when adjusting the level. If youre playing single notes for the part, simply play one string for now, preferably the D or G string.

OK, you should be hearing the guitar signal. If you have no sound or metering, pull down all the volume controls in the path as well as the master volume control and check your routing path. In haste, I still sometimes make stupid mistakes when doing the routing. Take your time and slowly think through the path. It is always best to start at the beginning (the amp).

 

Plugging in the compressor

Now that all of the above has been performed we need to insert the compressor in the signal path. There are a few ways to do this. This set up is basically for an analog or digital mixer that has insert patch points on each input module OR has a patch bay (or outputs on the back of the mixer) that allows patching from mixer busses to recorder inputs. The digital routing is explained as well.

 

On module #9:

- If you're using a hard disk recorder with compressor plug-ins, simply route one to soft module #9. - If you're using a digital outboard compressor and a digital mixer, and if the compressor and mixer allows for digital wire or light pipe connections, plug into the insert patch point (if available) on module #9. If there is no insert digital connection on the mixer, there may be digital connections at the module output into the digital recorder. In any case, the following will relate so simply adapt. - If you're using a mixer with built in compressors on each module, simply switch in. If you want to use an outboard compressor instead, he we go: - If youre using an outboard compressor, and if there is an insert output and input patch point on mixer module (module #9 in our example), patch the insert output into the outboard compressor input and patch the compressor output into the insert input. The mixer may have a switch to activate the insert. If so, switch in. - 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. - If there is no insert patch point, the mixer will surely have bus outputs and possibly direct outputs that route to the recorder inputs. Simply patch the bus or direct module mixer output used for the guitar track (bus #7 in our example or a direct output from module #9) to the compressor input and patch the compressor output into the recorder track (track #7 in our example). For this patching, the EQ will be before the compressor, which is what we want as explained next.

 

Positioning the EQ in the chain

If you're using a digital recorder/mixer combination, simply position the compressor in the soft path AFTER the EQ, meaning post-EQ.

The mixer will typically have a switching mode to position the insert path pre-EQ or post-EQ. If there is no switch the odds are good the EQ will be positioned after the EQ. If there is a switch, set it to post-EQ since we want the compressor to see the EQ (if EQ is being used).

 

Adjusting Compressor Settings

If you're engineering and you are not the guitarist, ask the guitarist to play the part for the song that he or she will be recording. While the guitarist is playing, adjust all the compressor (or limiter) settings to taste using the settings explained above as a guideline.

If you are the guitarist, and if the part you're going to record involves playing chords, play open strings with one hand and adjust the compressor settings with the other. Play the amount of strings that you would use for the rhythm part, meaning if the part requires just the upper four strings, just play those strings using the typical stroke pressure you would use when playing the rhythm. If you're playing a solo or a single line part, play open strings one at a time. When playing the solo or line, you will most likely need to tweak settings. I typically record around 8 bars and then playback. If adjustments are needed, I tweak compression settings, EQ, and possibly level settings. I do this as many times as needed. When happy with the settings, its time to have fun playing the solo or line. I'm getting ahead of myself and we still need to talk about levels, so here we go:

The compressor (or limiter) will have some type of level indicator. If it is an analog compressor using a VU meter, and if the input control is not the same as the threshold control, disable the compression and set to average zero dB on the meter. If the input level and the threshold are the same, the VU meter will show that compression starts past zero dB on the meter. In many cases, the compressor will offer a meter mode showing the amount of compression. In any case, adjust the compression level to taste as well as all other settings available.

The same applies to other types of metering such as LED, etc. In this case and for analog recorders, its best to stay out of the red to avoid possible distortion. If you're using a digital unit, I NEVER LET THE SIGNAL GO PAST ZERO since digital distortion is very ugly sounding! Its best to set the level to not go past 4 on the meter. OK, many engineers say that hitting the red a bit in digital land is not a problem since that is only a few samples that got chopped off into a square wave. Again, there are no rules.

OK, after doing the above, if you're using a separate recorder and mixer, look at the recorder track meter for the guitar. Are you seeing a similar level on the recorder meter set to a logical level before adding the compressor into the chain? If the level is lower or higher, if the compressor (or limiter) has an output volume control, set to the level before you added the compressor in the chain. If you're having problems setting levels to match there could be a mismatch in gain structure. The mixer may be a 10 design and the compressor may be a +4 design or the reverse. Further, the mixer and recorder could be gain mismatched as well.

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