Analogue Warmth

Analogue warmth seems to be the Holy Grail in these digital days. But what is it, why does it hold such appeal, and how can you use it to enhance your recordings?

Hugh Robjohns

Get a group of recording engineers together, and sooner or later the conversation will turn to a discussion (probably quickly escalating to an argument) about ‘analogue warmth’ and how things sounded so much better ‘BD’ (Before Digital) — and even engineers and musicians who’ve never worked in earnest with all-analogue systems (digital having become mainstream as far back as the 1980s) seem keen to bring this perceived ‘warmth’ into their productions.

What Is Analogue Warmth?

Not everyone has had first-hand experience of magnetic tape recording and other analogue recording technology, of course, but we’ve all heard and admired the vast back catalogue of classic records made using this technology from the 1950s onwards.

There are many factors that combine to create character in recordings, ranging from instruments, musicians and performances, through the rooms and mics used, to the preamps, processors and effects (and the way in which they’re used), but when we talk about analogue warmth, we’re usually referring to the character that the analogue processing/recording equipment and the recording medium add to the sound.

In this article, I’ll look at some of the key analogue technologies often associated with ‘analogue warmth’, and explain why they create the sound they do. Hopefully, this will enable you to make more informed gear choices and create mixes with an analogue feel, if that’s what you’re after. Some of ‘the science’ may seem daunting, but the alphabetical ‘Technical Terms Explained’ boxes should help with that.

Analogue Versus Digital

I cut my professional teeth on analogue equipment, but I think modern digital recording is a significant step up from the best of analogue in many practical ways. A lot of the early digital gear certainly didn’t live up to the hype that surrounded it, but understanding and technology have come on in leaps and bounds since then, and to my mind digital recording systems can now deliver pretty much all that was once promised: a near-perfect recording medium that gives back exactly what was recorded.

That’s great in some circumstances, but it’s not always what we want: in many cases, the technical limitations and imperfections of analogue systems have become an integral part of the quality of the recorded sounds that we all grew up with — and the end result is perceived by many people as being more pleasing than we can easily achieve today with all-digital recording chains. Further than that, some of the sounds resulting from ‘abuse’ of analogue gear have become recognised effects in their own right (tube overdrive and tape saturation being obvious examples).

Interestingly, sound recording isn’t the only industry that has found this. Digital cameras and imaging software usually provide a range of ‘picture-style image processing’ options. My own camera offers Standard, Portrait, Landscape, Neutral, Faithful, Monochrome, and three user-defined modes, for example, each changing the tonal balance, colour saturation, sharpness, and contrast in different ways, to enhance the subject

In short, enjoyment of an artistic product (be it a sound recording, a photograph, a film or whatever) isn’t necessarily about precision and accuracy: more often, it’s about mood, character and subtle enhancements that make the end result more vivid and interesting than real life.

When it comes to audio, some aspects of analogue technology introduce artifacts and distortions that are perceived as pleasant, and are often musically enhancing — and this is something that lies at the heart of the idea of ‘analogue warmth’. Of course, mechanical equipment can be expensive or impossible to acquire, and a hassle to maintain or use. Small wonder, then, that so many people seek (and so many manufacturers now provide) software and hardware tools that aim to reintroduce some ‘analogue character’ into digital production chains. Some of it works well, some of it not so well — but what is it actually trying to emulate?

Heat Factors

Until now, I’ve talked rather generically about analogue equipment — a term that encompasses a whole world of microphones, tape, valves, transformers and other electronics. Take a look at the diagram of a reasonably simple analogue recording/mixing chain elsewhere in this article, and you’ll see why: multiple opportunities exist to add colour and character to a signal before the master recording is created. There are clearly several factors that make up ‘analogue warmth’ and our ears almost certainly require a combination of all of them; focusing on only one doesn’t seem to deliver a truly convincing result. I’d sum up the most important factors as:

Magnetic recording tape, and the mechanical artifacts of the tape machine itself, such as flutter and other speed-stability issues.

Harmonic and non-harmonic distortions, such as those caused by transformers and inductors.

Active circuitry, whether it includes valves (vacuum tubes) or solid-state devices.

Alongside these, we also have to consider frequency response and dynamics. Ribbon mics, monitor speakers, recording tape and many valve-stages dating from the 1950s and ’60s often had restricted high-frequency performance and a fuller bottom end, for example, and they also tended to reduce the dynamics of signal transients, through thermal or magnetic ‘saturation compression’ effects.

As well as the direct influence this equipment had on the sound, it will also have influenced recording and mix decisions, such as mic selection — with brighter-sounding condenser microphones being chosen, for example, or high-frequency EQ boosts being applied with the knowledge that the top-end emphasis and transients would be smoothed by the recording chain.

The Reel Thing

Of the three factors I’ve listed above, the one most obviously absent in recording chains these days is the analogue tape recorder, with professional machines now too expensive and maintenance-intensive for most people to consider practical.

Most audio aficionados are probably aware to some extent of the sonic influence of magnetic tape, but fewer will have considered the influence of the tape machine itself. The biggest problem for any mechanical tape transport system is speed control, and the imperfect nature of this control produces artifacts that are generically lumped together as ‘wow and flutter’. There are actually four distinct variants of this, namely ‘drift’ (which shows up below 0.1Hz), ‘wow’ (0.1-10Hz), ‘flutter’ (10-100Hz), and ‘scrape flutter’ (in the 1-5kHz region). To explain the last term, which you may not have heard, as tape is dragged across the tape heads under tension, its movement sets up a vibrational resonance along the length of unsupported tape between the heads and/or the preceding rollers or guides — just like a violin string being excited with a bow. This resonance will tend to cause the tape to vibrate against the head, effectively causing it to move in a series of short, rapid jerks, which we call scrape flutter.

Fifty years of tape-machine design evolution reduced wow and flutter to extremely low levels by the 1980s, but it couldn’t be removed completely, and even the mighty Studer A820 two-track machine’s specifications quoted a wow and flutter figure of 0.04 percent when the tape was running at 15ips (inches per second). This is a tiny amount, certainly, but word-clock stability — which is the equivalent of wow and flutter in modern digital systems — can’t even be measured, as digital systems are orders of magnitude more stable in the time domain.

So what audible effect would such low levels of wow and flutter introduce? Well, the minute cyclical speed fluctuations of flutter, and particularly scrape-flutter, create subtle ‘side-bands’ (see ‘Technical Terms’ box) and noise modulation around the recorded audio. These add a perceptible low-level ‘grunge’ to the sound, and while better-designed and maintained tape machines suffered lower levels of this grunge, it was always there to some extent. Although technically flutter is a fault, many argue that its side-bands and noise-modulation effects are an intrinsic part of the sound character of all analogue tape recordings, and that we’ve come to accept (and expect) them as part of recorded sound — and as part of what we call analogue warmth.

The more bounce-downs that are done on the same tape, the stronger these effects become, as each recording pass adds to the grunge, and this made the associated sound character more prevalent in the late 1970s and the 1980s, when large multitrack recording formats became commonplace and lots of overdubbing and bounce-downs were routine.

These once-common recording attributes are absent from all digital recording chains, and I don’t know of any software plug-ins that claim to recreate the specific grunge effects of wow and flutter. A few claim to include some element of wow and flutter in some operating modes — one such example being Digidesign’s Reel Tape Suite — but to date I’ve not heard one that I’ve found truly convincing in this respect.

Tape Saturation

Most people reading this article will have heard about the idea of tape saturation, and the key role it plays in creating ‘analogue warmth’. This is another complex area, but one that more companies have been successful in simulating, both in analogue hardware and in digital plug-ins. Analogue recording tape is inherently ‘non-linear’, its effect being determined by a combination of tape formulation, record and replay head construction, tape speed, tape width, record and playback equalisations (and phase shifts), and the level and waveform of high-frequency bias. Plenty of variables to play with there! These parameters introduce distortions of harmonic content (particularly at low frequencies), and frequency and phase-response irregularities, and they reduce dynamic range, mainly affecting high-frequency transients through magnetic saturation and ‘self-erasure’ effects (see explanation overleaf).

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Analogue Warmth

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