Working Around a Level Mismatch

Working Around a Level Mismatch Brought to you by: guitar.com

Just Press Play Logo Gif 16698The following applies to all analog outboard gear and digital outboard gear that allow analog routing. Even if using a digital mixer or a mixer/hard disk recorder, the odds are good there will be analog inserts for outboard gear. There are two basic gain structures used for recording gear. Inexpensive to mid-line gear usually incorporates a 10 dB gain structure. Some mid-line through pro gear incorporates a +4 dB gain structure. Some units have a switch for either 10 or +4 levels. In some cases, the same goes for stand-alone mixers and recorders. Obviously if switch-able, match your gear levels.

When using gear that is not level matched, the gain path either needs to be made up for, dropped down and possibly brought back up. Let's use a compressor for the work-a-rounds. As usual, the guitarist will obviously need to play at the full level the part will be recorded with when dealing with mixer/gear/recorder chain level settings.

Plugging in the compressor

Well be using the same mixer/recorder setup as detailed in previous columns. If you need to review that setup, read Part 3 Miking the Guitar Amp. You may also want to review parts 10, 11, or 12 (about compressor setups). Otherwise, here are compressor suggestions for dealing with level mismatches:

 

On module #9:

If you're using a digital outboard compressor and a digital mixer, keep in mind that if routing digitally, there will not be a gain mismatch problem. Analog routing may create level mismatches. Again, we are using an outboard compressor using analog routing. If there is an insert output and input patch point on the 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 you have 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).

 

Setting the Levels on the Compressor

The compressor (or limiter) will have some type of level indicator. If you're using an analog compressor using a VU meter, and if the input control is not the same as the threshold control, disable the compression (use the compressor bypass switch) and set to average zero dB on the meter. If the input level and the threshold are the same pot, 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 with analog recorders, its best to stay out of the red to avoid possible distortion. If using a digital unit, I NEVER LET THE SIGNAL GO PAST ZERO since digital distortion is very ugly sounding! Its best to set the loud peaks to not go past 4 on the meter. OK, some recording engineers say that hitting the red a little in digital land is not a problem. I disagree, but there are no rules. Note that some digital gear manufacturers set the metering to allow for a few dB of headroom past zero on the meter. I do not like the concept since the user should know the true clipping point. 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, and if the compressor (or limiter) has an output volume control, set it to the level before you added the compressor in the chain. If you need to review details regarding levels in full, refer to the basic 9-step set up information in Part 3 Miking the Guitar.

 

Dealing With the Level Mismatch

When adding gain (-10 dB compressor and +4 mixer), its always best to add in the beginning of the signal chain. i.e., the guitar mic pre-amp for mixer module #9, and or mixer module #9s fader (and or trim pot if a separate trim for the line level path). When dropping gain (+4 dB compressor and 10 mixer), its always best to lower the gain as far down in the chain as possible. In either case this helps keep the noise (electronic hiss) down in the signal path.

 

-10 dB Compressor with a +4 Mixer/Recorder Chain

If you're using a 10 dB outboard compressor and a +4 dB mixer and recorder, the compressor will see too much level at its input using a normal input level setting. If the compressor has an input volume control separate from the threshold control, turn off the compression (bypass switch) and set the level as mentioned in Setting the Levels on the Compressor. OK, after setting the basic input level, its time to jack up the level as far as possible without adding distortion. Crank up the input level until you hear distortion and then pull back at least 4 dB on loud notes to allow for some headroom. Activate the compression (switch out of bypass) and adjust the threshold and other compressor settings to taste. If the compressor has an output volume control, bring up the level as noted in Setting the Levels on the Compressor. If you have no compressor output volume control that will be covered as you read on.

Lets say that the compressor does not have a separate input level control. In that case, the threshold level control is also the input level control. Set to achieve the desired compression. If the compressor has an output volume control, bring up the level as noted in Setting the Levels on the Compressor. If you have no compressor output volume control, that will be covered as you read on.

In either of the above two examples, if you have no output volume control on the compressor, and if you're using the insert patch point on the mixer module used for the guitar mic (mixer module #9 for our example), the odds are good that bringing up mixer module fader #9 will not affect the send level to the compressor. Thats good news, so bring up the fader to achieve the proper level as noted in Setting the Levels on the Compressor. Most likely you will be bringing up the fader to the top of its throw. If you need more level to the recorder, and if youre using bus #7 to feed recorder track #7, the odds are good the mixer has a sub master level control for each bus. In that case, the odds are you could add gain using the bus sub master level control for bus #7.

If you're patching into the compressor via mixer module #9 using bus #7s output to the compressor, or patching mixer module #9s direct output into the compressor, and patching the compressor directly into recorder track #7, and if the compressor does not have an output volume control, perform the following: Patch the compressor output into an unused mixer module and patch the direct output of that module into recorder track #7s input. Use the newly patched module to get the necessary level to the recorder. By now you should have enough gain but, if not, use the trim pot on this module to get the needed gain. Note that since this mixer module is only being used for the compressor return to the recorder input and no mic pre is used in this path, and if the mixer module only has one trim pot for any type of input signal, it will be active.

 

-10 dB Compressor with a +4 Mixer and a 10 dB Recorder Chain

All of the above applies and the only difference is to lower the level to the recorder input. There are a few ways to pull this off.

If the compressor output is not patched directly into the recorder, and if using mixer module #9 for the insert send and return for the compressor, the odds are good the mixer module level will only affect the level to the recorder. In that case, set mixer module #9s fader to achieve the proper level to the recorder track. Refer to Setting the Levels on the Compressor if need be. If the compressor output is patched directly into recorder track #7, and if the compressor has an output volume control, adjust it to achieve the proper level to the recorder track. Refer to Setting the Levels on the Compressor if need be. If you have no output volume control, you need to use an unused mixer module to drop the level to the recorder track input. In that case, patch the compressor output into the unused mixer module and either bus to an unused bus or patch the direct output into recorder track #7. Set the new mixer modules fader to achieve the proper level to the recorder track. Refer to Setting the Levels on the Compressor if need be.

 

+4 dB Compressor with a 10 dB Mixer/Recorder Chain.

If you're using a +4 outboard compressor and a 10 mixer and recorder, the compressor will need major gain to cross the compression threshold. As mentioned above, its always best to get the gain as early as possible in the chain.

Using the insert patch points on Mixer Module #9 for the compressor. Since the odds are good the fader on mixer module #9 will only affect the level to the recorder and not to the compressor, the mic pre-amp is the first place to add gain. Crank up the mic pre-amp level on mixer module #9 to the point of hearing distortion. Now back it down about 4 dB on the loud notes to allow headroom. Now set the compressor input level as explained in Setting the Levels on the Compressor. The odds are good you have enough gain to work with the threshold setting. If you still need more level to cross the threshold, use the routing explained below in Using mixer bus #7 output or mixer module #9 direct output to feed the compressor.

Regarding the compressor output level for this routing, if the compressor has an output volume control, set it to unity gain (marked by zero next to the pot). Mixer module #9 should be set to unity gain (zero marking on the fader throw, typically 3/4ths up on the throw). Refer to Setting the Levels on the Compressor and use mixer module #9s fader for the proper level to recorder track #7. The mixer should have at least 15 dB of headroom (the low headroom standard) so the level from the compressor should not distort mixer module #9s input. On the other hand, if you are hearing distortion using an inexpensive mixer with very little headroom, set mixer module #9 to unity gain and use the compressor output volume control for the proper gain to recorder track #7. If the compressor does not have an output volume control, use mixer module #9 for the level setting. (Lets hope the mixer has at least 15 dB of headroom in this case.)

Using mixer bus #7 output or mixer module #9 direct output to feed the compressor. In this case, mixer module #9 will affect the level to the compressor. Set mixer module #9 all the way up on its fader throw. That should get around 10 dB of gain, which should be enough. OK, if that's not enough gain for a compressor without an input level control, use the mic pre-amp trim on mixer module #9. So why not use the mic trim first as in the insert patch point? You could but I went with the fader thing to allow a good amount of headroom within the mic pre-amp circuit and then add at the mic pre trim if needed. (Yes, this adds a slight bit more noise but, in guitar amp land, the noise from the amp is much more noticeable. If you're recording something like a vocal, you surely want to keep the noise down and using the mic trim for the gain would be best).

With this routing, the compressor output is patched into recorder track #7s input. Since we are going from a +4 output to a 10 input, the gain obviously needs to be lowered. If the compressor has an output level control, great. Simply adjust as needed in Setting the Levels on the Compressor. If you have no output level control, you will need to patch the output into an unused mixer module. Simply patch the compressor output into a non-used mixer module and either bus to an unused bus or patch the direct output into recorder track #7. Set the new mixer modules fader to achieve the proper level to the recorder track. Refer to Setting the Levels on the Compressor if need be.

 

+4 dB Compressor with a 10 dB Mixer and a +4 dB Recorder Chain.

All of the above applies. The obvious difference is the level needs to be bumped up to the recorder.

If the compressor output is not patched directly into the recorder, and if using mixer module #9 for the insert send and return for the compressor, the odds are good the mixer module level will only affect the level to the recorder. In that case, set mixer module #9s fader to achieve the proper level to the recorder track. Most likely you will be bringing up the fader to the top of its throw. If you need more level to the recorder, and if youre using bus #7 to feed recorder track #7, the odds are good the mixer has a sub master level control for each bus. (Note the bus is after the insert patch points and will not affect the level to the compressor input.) In that case, the odds are you could add gain using bus #7s sub master level control. If you have no bus sub master level control and need more gain, use the routing that includes another mixer module, described below. When setting levels, as usual, refer to Setting the Levels on the Compressor if need be. If the compressor output is patched directly into recorder track #7, and if the compressor has an output volume control, adjust to achieve the proper level to the recorder track. Refer to Setting the Levels on the Compressor if need be. If you need more level to recorder track #7, use the following routing. If you have no compressor output volume control, you need to use an unused mixer module to add level to the recorder track input. In that case, patch the compressor output into the unused mixer module and either bus to an unused bus or patch the direct output into recorder track #7. Set the new mixer modules fader to achieve the proper level to the recorder track. If you need more level to the recorder, and if patching the compressor output directly into recorder track #7, change the routing to use bus #7 to feed recorder track #7. The odds are good the mixer has a sub master level control for each bus. In that case, the odds are you could add gain using bus #7s sub master level control. As usual, refer to Setting the Levels on the Compressor if need be.

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