Direct injection (very frequently abbreviated to DI) is the apparently simple practice of sending the output of an electric or electronic musical instrument straight to a mixing desk or recording setup. It's an alternative to putting a mic in front of an amplifier, and it's a highly desirable alternative, because it saves a lot of setup and soundcheck time, cuts out problems with sonic leakage, and makes everything more predictable and manageable.
With some instruments - keyboards, drum machines, etc - direct injection really is as simple as it sounds. But with electric guitars? Nope. It took the full might of the music tech industry many years to develop a way to directly inject a rock guitar without losing its critical essence. Many would contend that it still can't be done without losing a little je ne sais quoi, but since the 1990s there's at least been an array of widely acceptable solutions. This post charts the historical progression of direct injection for guitars, from crude yet effective successes in the pre-digital age, to mass market monetisation of what in many ways was, and is, the recording guitarist's Holy Grail.
IN THE BEGINNING
If you timewarp back to the 1970s and early 1980s, you can listen to various pop classics, marvel at the guitar sound and think: “Wow! That is one hell of an amp”…
But in some cases you’d be wrong. Some of the great guitar sounds of the pre-digital age, in actual fact, turned out to be the result of guitarists simply plugging their instruments straight into a studio mixing desk, sprinkling on one or two effects and a bit of EQ, and calling it a take. “One hell of an amp”, in reality, was no amp at all.
The shockingly underrated British rock ‘n’ roll guitarist Mickey Gee was known for this approach, and his some time colleague Dave Edmunds has acknowledged recording with direct injection in the '70s too. If you listen to Mickey Gee's brilliantly-crafted work on Shakin’ Stevens’ mammoth 1981 hit You Drive Me Crazy, you’ll hear how present and musical clean electric guitars can sound in a mix, when not robbed of harmonics by a guitar amp and speaker.
Before the progressive DI epiphany of the 1980s, that was the whole point of using direct injection for electric guitars: to preserve the full harmonic content of the instrument’s output. In most cases, during the pre-digital age, the direct injection of electric guitars was confined to clean tones. A clean electric guitar did, and still does sound great with all its harmonics intact. And of course, it would be silly to suggest that 1970s guitarists were the first to use direct injection. Sending clean electric guitars straight to a mixing desk is a concept that will inevitably have precedents dating right back through rock 'n' roll history. Hendrix, for example, is acknowledged to have used direct injection for some clean tones in the 1960s, on the advice of one Mr Les Paul, who of course used the technique much earlier.
But there was a huge question mark over the compatibility of distortion and overdrive sounds with direct injection. A distorted guitar has a buzzy, dissonant top end, which most listeners regard as undesirable. Guitar amps and speakers will smooth out this buzz or fizz by filtering the dissonant high harmonics. But sending the output of a distortion effect straight to the mixer would reproduce all of the nasties.
In some instances, distortion was directly injected in the pre-digital age, but in professional circles, only on a very exceptional basis. It took some pretty brave and forward-thinking creatives even to release material featuring DI’d guitar distortion before the 1980s, let alone actually succeed with it.
The ultimate exception to this rule is Thomas McClary’s solo on The Commodores’ hit Easy. Regarded as one of the best guitar solos ever, the line has all the classic hallmarks of 'wasp in a jam jar' DI distortion. Many will say it works because of what was played – not because of how it was recorded, but the direct feed and consequent alien nature of the sound within the mix, does make it stand out in a way it otherwise wouldn’t. It was the right approach for recording that solo. Genius really, and a very bold step on such an otherwise slick track.
By the middle of the 1990s, flashy pre-amps with direct-to-mixer outputs were big business in the world of electric guitars. But early in the previous decade it was a very different story.
DIRECT INJECTION EPIPHANY
The epiphany period, during which guitarists and the tech industry unified their respective goals and provisions regarding direct injection, would run for over a decade. Through the early 1980s, there was a progressive development from so-called ‘power soak’ technology to the initial attempts at amp simulation. Tom Scholz spearheaded this innovative initial phase with the commercial release of the Power Soak in 1980, and later, the famous Rockman ‘personal amp’.
The Power Soak was not an amp simulator, but a means of permitting an amplifier to be driven hard (and thus facilitating the desirable sonic properties of a really loud setup), without the deafening volume. Placed between power amp and speaker, the Power Soak literally soaked up the power of the amp’s output level, so guitarists could get the richness and sonic vitamins of seriously cooking valves, at a more polite volume.
Whilst the Power Soak didn’t in itself simulate an amp, it did raise the profile of managing guitar volume in recording situations – something which would eventually become the preserve of amp simulators. But the point of the Power Soak was completely lost on so many people…
“But, like, does the amp’s volume control not turn down the volume?… Duh…”
It was again Tom Scholz, in 1982, who released the Rockman unit for electric guitar. This device specifically set out to eliminate the use of a regular guitar amp and speaker in applications such as personal practice and recording. As a product designed to offer distortion in contexts that didn't include a guitar amp, the Rockman needed some form of amp/speaker simulation to prevent undesirable fizz, and it implemented such a feature within the scope of the era’s technology. Historically, the Rockman was a hugely important piece of gear.
It was, however, interesting how few purveyors of guitar solutions followed suit and set about developing the amp sim concept. The Rockman idea was ripped off by copycats, but this was really just straight parroting. There was a distinct lack of manufacturers saying: “Ah, speaker simulation. Maybe we could develop that concept further.”
I do, however, recall from experience on the live music scene in the mid 1980s, that “power soak” had become a minor buzz phrase. Some people were experimenting with their own methods of limiting volume, and/or routing guitar amp outputs directly to the PA system, using dummy loads to avoid straining the amps when running them on mute.
One PA provider we met would use what looked like home-made DI boxes for guitars. The gadgets were different from the standard line-balancing DI boxes for PA, and they did sound like they were smoothing the top end of guitar signals so as to make the overdrive more palatable.
So at street level, the quest for volume-managed, and mic-eliminated rock guitar production was a happening scenario. It’s just that the bulk of the tech industry was still to catch up with what was going on. The real problem most likely lay at distribution and/or board level. Inventors knew the value of amp/speaker simulation, and guitarists who’d experienced the frustration of owning equipment that performed best at prohibitive volumes were obviously interested. But the facilitators and distributors didn’t have the same insight. Their attitude was:
“WTF? Why would anyone buy an amp with speakers, and then disconnect the speakers?…”
They just didn’t get it. They couldn’t visualise anyone buying the gear.
HUGHES & KETTNER RED BOX AND CREAM MACHINE
But in the second half of the ‘eighties, the street level experimentation and crude, duct-tape-encased magic boxes did start to appear as professionally-made products. Hughes & Kettner’s Red Box was a very notable example of a transitionary device which formed a bridge between the power soak and the standalone amp simulator.
I’d say the Red Box was very similar to some of the DIY contraptions people had been using. But it was clearly more sophisticated and better made, and crucially, it was in the magazines. The Red Box is to a considerable extent overlooked today, and whilst its capabilities were extremely limited, it was really the first device to go right into the thick of the UK consumer market and say: “Hey! Speaker simulator! Full stop.”
Hughes & Kettner also integrated their Red Box ‘Cabinetulator’ technology into the Cream Machine, which served as a complete, valve-driven, power-soak-integrated, direct-to-desk recording solution for overdriven and distorted electric guitar – from 1988. Although these H&K products were reviewed in rather an unenthusiastic tone in Britain (it probably didn’t help that the manuals were written in German only), they were a milestone, and years ahead of the market. Whilst other companies were still trying to sell Dalek Flangers to spandex-clad Dr Who fans, H&K were pre-empting the trend of the next few years. Due to H&K, every observant guitarist now knew what speaker simulation was all about.
Another early arrival in this first real burst of diverse amp sim toys came from Portastudio manufacturers Tascam. The Tascam GS-30 was clearly designed as an all-in-one solution for recording overdriven guitar sounds directly, without an amp or mic. But before the end of its highest-publicity UK review, the reviewer was primarily talking about routing it through a guitar combo – which totally defeated the purpose of the product.
None of these late ‘eighties gadgets were perfect solutions, and they all lacked versatility. You weren’t selecting from a range of amp models – you got one generic amp simulation, and that was that. It was commented in reviews at the time – I thought very fairly – that the standard policy for direct injection gadgets had thus far been to smother the overdrive sounds in additional effects, in a bid to divert attention away from deficiencies in the amp simulation. The first mass market devices to stop doing that (which included the H&K Red Box / Cream Machine and the Tascam GS-30) were inevitably going to face new levels of scrutiny. Even in their day it was hard for them to impress.
For reference, Paul White was pretty much the UK's lead reviewer of these early speaker and amp sim products. He was not easily pleased, but the tepid reviews probably helped the gadgets' cause in the long term. If everyone had gone out, bought, and been disappointed, there would have been a lack of trust when the more exciting simulations did start to arrive.
Notably, early guitar multi-FX processors did not feature any amp/speaker simulation.
PALMER SPEAKER SIMULATOR
The Palmer Speaker Simulator became the next UK DI sensation when it began to get major hype and publicity around summer 1990. However, this was only really a variation on earlier speaker simulators, packed in a rack format and therefore targeted at professionals – some of whom were virtually soiling themselves with excitement at its capabilities.
The Palmer took a significantly more complex stab at speaker simulation than the H&K Red Box, and it did have limited options to vary the simulated cab/speaker type. But it was not really a new concept. Priced at £225, it was also well over four times the cost of a Red Box, and even more expensive than H&K’s all-in-one Cream Machine, which offered real tube overdrive onboard. Unlike the Cream Machine, the Palmer did not dispense with the need for an amp.
UK advert for the original SansAmp. As you can see, by the time the product hit the UK market, it had already built up a big professional userbase.
THE ORIGINAL SANSAMP
Meanwhile, a new approach to direct injection had materialised in the original SansAmp. Manufactured by Tech 21, the SansAmp was a small all-in-one box, setting its teeth into the UK market in early 1991. On a very basic level it could be equated with the Cream Machine, and indeed it could directly replace the Cream Machine. However, the SansAmp’s overdrive was created with solid state electronics, and far more importantly, the character of the unit’s amp/speaker simulation could be extensively tailored.
With the SansAmp, the physical modelling of specific amp setups was finally now possible, although the amp brands were not marked or even implied on the product. Instead, the user would need to combine selectable modelling characteristics in recipes, but the manual did reveal which recipes would simulate specific classic amps.
The all-analogue SansAmp was initially pitched on its review rounds with a retail price of £178, but there was adverse reaction to that price, and it was actually lowered to £145 before at least one of the reviews had even hit the shelves. Now that things were starting to get competitive in the sphere of direct injection, price had become a bigger issue.
…AND THE DIE WAS CAST
It would still take some time before the best features from all of these groundbreaking developments were unified and better packaged for the consumer, but the die was now cast. In the course of the next couple of years, the market would adopt speaker and amp simulation en masse, completing an era of over a decade during which the knowledge and vision of the select few, had slowly become indispensable in the mainstream.
I've now posted an addendum to this article, in which you can hear an audio test of some oldie speaker simulations (including the original Red Box). You can find it in Guitar Speaker Simulations Audio Test.
If you use PC-based recording techniques, you can get a virtual version of a guitar amp simulator in the shape of this site's own freeware Stomp King SK-5 Guitar Amp VST plugin - as depicted above.