AF’s Weblog

February 4, 2011

Dynamics Processing Meets Rock Guitar: How to Compress a Guitar or Bass

Dynamics processing with studio-oriented processors? Been there, done that. But have you re-visited it lately in a guitar context? Dynamics control for vocals or program material is very different compared to guitar. Much of this is because there are many ways to use dynamics processing for guitar (or bass). So, let’s take a look at the different ways to apply dynamics, with examples of suggested settings.

For an introduction to compression, check out the article “Compressors Demystified.” If you’re already up to speed, let’s give a few basics on how to set up studio processors with guitar (however, note that these same basic techniques work with plug-in software compressors as well as hardware).

The Interface Space

“Stomp box” dynamics processors, while designed specifically for guitar, are more limited than rack-mount studio hardware – but the latter have issue levels with guitar. Interfacing involves one of four approaches:

Use the instrument input. If the processor has an “instrument” input, you’re golden. Plug the guitar directly into the processor, then run it into the mixer, amp modeler, guitar amp (assuming you can adjust the output level to avoid total overload), or whatever. Look for an instrument input impedance above 100kilohms, and preferably above 220kilohms, to avoid dulling high frequencies and reducing level. But too high an impedance (in the 5-10Megohm range) reaches a point of diminishing returns, because now the input may be too sensitive and prone to noise pickup. A 1Megohm impedance is a good compromise setting.

Use a preamp or suitable direct box. Adding a preamp or direct box (assuming it has an appropriately high input impedance) before the processor will preserve the guitar signal’s fidelity and allow for best level matching. If you’re driving a guitar amp, you may be able to use the dynamics processor’s output control to add some extra overdrive, but don’t go overboard (or do, if you like really nasty sounds!).

Insert into your guitar amp’s effects loop. If you want to record with your guitar amp but are using a line-level processor, patch it into the guitar amp’s effects loop. The loop should be able to provide line levels for the send (goes into the processor’s input) and return (comes from the processor’s output).

If you’re using a hardware mixer, insert the dynamics processor into your mixer’s channel inserts. This will also match levels properly, although you’ll still have to figure out how to interface the guitar with the mixer. The choices are the same as above: If the mixer has an instrument input, great. If not, use a preamp, direct box, etc. between the guitar and mixer.

Now let’s take a closer look how to really do it…

Double Your Pleasure

Patching two compressors in series, with both set for small amounts of compression, can give a significant amount of compression but sound less obvious than using a single compressor to give the same amount of compression. The first stage essentially “pre-conditions” the signal so that the second compressor doesn’t have to work so hard.

 

If you have a stereo compressor that can be set to dual mono operation, you can patch the two individual compression channels in series. With plug-ins, you can just insert two in series in a track. The drawback is that unlike standard compression, where you have to adjust only one set of controls, an ˆ la carte approach requires adjusting both sets of compressor controls. While this might seem like a disadvantage, most of the time you’ll set them to similar settings anyway.

Window Shopping

To get an idea of what’s out there in compressor-land, visit a few retailers and manufacturers and you’ll see the choices are huge, ranging from under a hundred dollars to thousands (and thousands!) of dollars. But realistically, for the type of application we’re describing here, you don’t need anything too fancy – it’s not like you’re using the compressor to re-master vintage recordings for audiophile releases. Besides, these days technology is at a level where even fairly inexpensive devices can deliver excellent results.

 

In any event, all the above tips are just guidelines. Experiment with your dynamics processor, and you may find yet another way to exploit these perhaps unglamorous, but extremely useful, devices.

To read the full detailed article see:  How to Compress a Guitar or Bass

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