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Q. Why should I record real guitar amps with microphones when I can use virtual amps?

I've noticed that a lot of producers still like to record guitar and bass cabinets with microphones, even though there are loads of excellent virtual equivalents available. I was wondering what advantage those producers are gaining from not using plug-ins exclusively.

Leo James, via email

SOS contributor Tom Flint replies:

There certainly are many excellent virtual amp and effect processors on the market, and they have made it possible to create very convincing soundscapes without actually recording anything with a microphone. Indeed, at the demo stage, it is not unusual for bands and producers to mock up their song arrangements using only plug-in processors and virtual instruments. The problem is that if a whole project is recorded in that way, the end result can sometimes sound a little artificial or flat. For modern pop, where over-the-top processing is almost standard, an artificial sound might not be such a bad thing, but for other styles of music, microphone recordings are very important, as they introduce subtle spatial and tonal variations that the top producers know how to use to their advantage.

If, for example, you are recording a guitar cabinet, the sound will be affected by a whole range of factors which would not come into play if the guitar were simply plugged into an interface and processed with a plug-in. For a start, no two amplifiers sound the same, even if they are identical models. Each will have its own set of cabinet buzzes and resonances, as well as a unique tonal characteristic due, in part, to electronic component tolerances and the varying affect of temperature on the circuit (to say nothing of potential valve noise and amplified mains hum). Furthermore, apart from the standard overdrive and EQ controls, most amps offer a reverb (and sometimes even a tremolo effect, too), and these deliver quite different results to those achieved with equivalent DAW effect inserts.

The mics that are used to record the cabinet also have the potential to dramatically colour the sound. Each design, whether it's a condenser, ribbon or dynamic, will have its own way of responding to the amp's output, and what the mic captures will vary enormously depending on how far from the cabinet it is placed and its angle and height in relation to the speaker cone. A mic will also pick up reflections from the room, further enhancing the spatial character of the sound, and another layer of distortion and noise will be added by its internal circuits and wiring. Finally, before the signal reaches the hard drive of the DAW, it may also be fed through a compressor, subtly changing its characteristics even further.

Producers don't just take advantage of the variables in the signal chain; they also expect the musician to respond in a positive way to the 'live' sound they are experiencing. Playing with feedback from the amp and tweaking pedal and amp settings during a performance is certainly something that can be explored more easily with a hardware setup. While amp sims are widely used and very effective, many top producers prefer to use the real thing in their productions, to add depth and character to their sound.While amp sims are widely used and very effective, many top producers prefer to use the real thing in their productions, to add depth and character to their sound.Q. Why should I record real guitar amps with microphones when I can use virtual amps?

At one time, virtual amps and processors were only really used for demo work, but their algorithms have improved a great deal in recent years, so it is now common for producers to mix their virtual guitar demo parts and microphone recordings together, rather than intending to replace the former with the latter. This actually makes a lot of sense, as mixing layers of sound is an age-old production trick many producers rely on to enhance their recordings. I even recall one producer saying to me that, in their opinion, professional producers typically go to much greater lengths than amateurs when creating and shaping their timbres, and that going that 'extra mile' was the key to achieving a professional sound.

A few years ago, I was lucky enough to interview Martin Rushent, who revealed something about his work on the Stranglers' first two albums which reaffirmed the notion that producers develop sounds far more than is immediately apparent to the ear. The Stranglers' albums in question had been recorded very quickly to capture the raw feel of the band playing live, yet it turned out that even on those supposedly 'unproduced punk' records, almost every sound was multi-layered and cleverly processed in some way. Of Dave Greenfield's keyboards, Martin said, "Dave had a Hammond L100 and Leslie cabinet so we used to take a DI out of the L100, mic up the Leslie top and bottom, and I think he may have had an amp as well, which we'd have miked. And we mixed the whole lot together, bouncing it to stereo there and then”.

Recording the bass was a similar process, as Martin went on to explain: "I also recall that it used to be a little thin out of the amp. Not desperately so, but it didn't have a real sub, so I think we picked that up off the DI and EQ'd the signal. Then we'd blend the two together.”

Today's producers are evolving working methods that are tailored to the digital environment and built around the software tools that make up DAW systems. These methods often involve mixing traditional-style mic and DI recordings with virtual amp simulations and heavily processed samples.

Steven Wilson, whose interview we featured in June 2010, is a good example of a modern producer who has embraced digital editing and virtual instruments, but also makes good use of microphone recordings. He usually starts by creating fairly elaborate demos in his home studio before performing a tracking session in a commercial room using real amps. "I'll go through and try to get better tones with the guitars,” he explained. "That's not always possible and sometimes the virtual tones have become so integral to the sound world of the track that they just work. I've never been snobby about using simulations and virtual instruments — if they sound good, use them!”

So, to sum up, there is no reason not to use plug-ins extensively if they are working, but microphone recordings can add variety and depth, which might just be what's needed when a track is sounding a little bit flat. The key may be to experiment with 'sound mixes' and keep going until they sound right.