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Capturing Lifelike Guitar Sounds Without Microphones: Part 1

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If you're recording anything acoustically, or playing live through a PA, microphones remain the usual and accepted route for capturing guitar sounds. From studio exotica costing thousands of pounds down to handheld and USB devices, the microphone reigns supreme.

As popular as this is, however, there are some drawbacks.

The relationship between the mic and its source needs to remain the same. The slightest movement in any plane of direction can change both the tone and volume of what’s captured. Anyone who's tried overdubbing an acoustic guitar part will know the challenge of creating a consistent recording.

Then there's the question of noise. Whether it comes from the recording space or stage, the player, the instrument, or even the recording equipment, all this can diminish the resultant quality.

You may believe that there's no alternative.

DI

This stands for Direct Injection, and refers to connecting an instrument electronically to an amplifier or recording device. For guitarists, whether recording or playing live, DI means capturing sound via the instrument’s onboard pickups.

For acoustic guitars, the most common pickup is the piezo. A crystal located under the guitar’s saddle, it translates vibrations from the strings into a small electrical signal.

Coupled to an onboard or external preamp, this is the sound audiences hear.

It certainly gets around the issues of using mics, and is ideal for a noisy live environment. However, because the piezo’s at the bridge, it captures the sound of the strings, but very little of the guitar’s body. It's okay for live work, especially in the context of a larger band sound. For recording, however, definitely not.

As for electric guitars, electromagnetic pickups are the norm. You can DI them very easily, but as with an acoustic guitar, you won’t get the sound you expect to hear, as you’re missing crucial elements of the overall sound, such as an amp and its speakers.

What is required, therefore, is something that sounds as good as a microphone recording, but with all the benefits of DI.

Thankfully, there’s a way to achieve this.

Impulse Responses (IRs)

I first came across these nearly 20 years ago. I’d just finished recording with a band, and the engineer was creating rough mixes. He knew I was interested in recording and production, so he clicked on a plugin, and said, “Listen to this”.

The sound of my band was suddenly given a really live, cohesive feel, despite having tracked each part separately in an sound-deadened room. The plugin was imprinting the recording with the acoustics of a rural church somewhere in the middle of the American Mid-West. 

I was fascinated both by how lifelike it sounded, and the possibilities it represented.

How Impulse Responses Work

An impulse response is a measurement taken of anything that deals with acoustics, be it a space, a speaker, or an instrument. Particular audio signals are either played through it or into it, and the resultant response is captured. Whatever this response is applied to then exhibits the characteristics of the original.

To start with, IRs were usually limited to reverb plugins, with Altiverb being one of the most well-known.

Reverbs still remain the most ubiquitous use of IRs, to the point where some DAWs have IR-capable plugins as standard. Logic’s Space Designer is one such example.

But as technology and processing power advanced, IRs have moved beyond just reverbs and this is where guitarists get involved. 

In the next tutorial I’ll examine acoustic guitars, but for now, I'll show you how IRs assist the recording of electric guitar amplifiers.

Electrickery

To this day, recording the sound of an amp and its associated speakers usually involves one or more mics being placed strategically around it. Even live, most sound engineers expect to mic up a guitarist’s combo or cabinet.

Some amplifiers have an emulated speaker output. This allows a DI connection between the amp and either a DAW interface or PA system. They’re very useful, but they’re slightly misleading. 

The emulated speaker is in fact the application of EQ to create a reasonable facsimile of a guitar speaker. It does the job, but doesn’t fully capture how a speaker works, or indeed, the influence of the speaker cabinet on the resultant sound.

An increasingly common occurrence in studios is to DI the amp and then use IRs to apply the sound of speaker cabinets. 

There are several reasons why this is a good idea.

Record Silently

Valve amps in particular really come alive as volume increases, but this isn’t always appropriate to every recording situation. Using DI means you can crank the amp without the resultant high levels of volume.

A word of caution, however.

Amps are designed to supply certain levels of current in order to drive speakers. If the speakers aren’t there, the current has nowhere to go, which can cause permanent damage to the output transformer

If you wish to record silently, and thus cannot attach speakers, you’ll need to use a reactive load box.

You Don’t Need Expensive Mics

Nor do you need mic preamps, an acoustically-treated space, or even knowledge of mic placement.

You Don’t Need a Selection of Speakers

Instead of spending thousands on different speakers and cabs, you can select from a huge range of IRs.

You Can Change the Tone

If you're not happy with the sound, just change the IR. This also means you can audition different speakers until you’re happy.

Conclusion

IRs are becoming more and more popular, and with good reason. They represent sounds of spaces and equipment at your fingertips that you wouldn’t otherwise have access to. 

Going direct means:

  • You get a consistent tone
  • Noise becomes less of an issue
  • The recording environment is less critical
  • You can change the sound during or after the recording
  • It’s a lot cheaper than owning lots of physical equipment

In the next tutorial I’ll show how IRs benefit acoustic guitars and their usage in the live environment.

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