Review: Avid Audio Heat
What else can you do to a cold digital recording? Apply some heat of course!
2 November 2010
Review: Brent Heber
Avid Audio recently announced ProTools HD version 8.1 and with this release came support for its new interfaces, upgraded I/O hardware and the David Hill designed HEAT option – the subject of this review.
HEAT is an acronym for ‘Harmonically Enhanced Algorithm Technology’. David Hill, the man behind this new ProTools option, is a bit of a legend in the audio industry, well known for his early work as founder of Summit Audio, and in more recent years, Crane Song. Crane Song in particular is renowned for its unique perspective on converter technology and analogue ‘warmth’ in the digital domain, most notably the innovative HEDD A/D – D/A that mastering houses the world over have latched onto in droves.
Dave Hill is as passionate about innovation as he is about avoiding replication – creating “clones of clones of clones” as he puts it – and many of his products have been specifically designed to “make digital sound better.” Who better then for Avid to turn to for adding ‘warmth’ to its HD mix engine?
WHAT IS HEAT?
First and foremost, it’s important to make one thing abundantly clear: HEAT is not a plug-in. It’s not something you insert onto individual channels and apply in varying degrees across different tracks at your discretion. HEAT is a new fixture (albeit optional) in the HD Mix window that’s designed to add a unifying colour and tone right across your mix – ‘glue and warmth’ some might simplistically call it.
The controls for HEAT appear across the top of the mix window on each individual audio channel as a simple two-button set, featuring ‘Pre’ (pre & post insert) and ‘Bypass’ controls, with an interesting horizontal meter that looks a bit like a cross between a valve lighting up and a Cylon’s eye, which displays how much ‘heat’ is being added to that track. These controls are made visible in the Mix window above ‘Inserts A-E’ (more on this in a moment). A master control set on the right-hand side of the Mix window then determines the nature of the saturation model you’re applying across all channels. Think of it like this: the buttons on the individual audio channels of HEAT represent the characteristic effects of individual channels on a multitrack tape machine, and the master control determines the brand and model of machine you’re recording to.
HEAT runs on the DSP chips of a ProTools HD Accel system within the mix engine itself. Using it across 60 mono tracks at 48k, for instance, will eat up two Accel chips. Not an insignificant portion of DSP, and this grows larger as more tracks are added to the fire.
NOT A SUMMING DEVICE
The cool thing about HEAT (if you’ll pardon the pun) is its non-linear nature; its behaviour is both volume and tone dependent. Better still this treatment is applied individually on a per-channel basis, as opposed to acting globally like, say, a sub-master bus compressor across an entire mix. The distinction to be made here is that, although HEAT’s master control determines the type of harmonic distortion you’re applying – call it a ‘global tendency’ if you like – the individual channels themselves don’t sum to the master controller first and then have HEAT applied subsequently to the premixed sound. Each channel gets its own individual treatment in the same way as a snare might when it’s recorded hard onto Channel 2 of a tape machine independently of the guitar solo, which might be striped to Channel 16. Sure, the two have been recorded onto the same tape machine – which has its own characteristic sound – but the individual recordings themselves don’t directly affect one another.
Moreover, it’s not only the gain structure of each track but also the frequency content that determines what processing happens on that individual piece of audio. So, for example, HEAT will affect bass guitar differently to hi-hats, differently to vocals, differently to piano, as they all inevitably possess different tonal characteristics and dynamic content.
And to press this point further, the Tone control on the HEAT master section is not merely some sort of post processing EQ. Rather, it’s an emphasis (or de-emphasis) to the harmonic distortion being applied to each track, adding yet another layer of complexity to the treatment.
HEAT can add two flavours of subtle low-midrange distortion. One is based on tape saturation alone, the other based on combining tape saturation with further analogue circuitry distortion, including tube saturation.
NEED TO KNOW
HOW IT WORKS
There are two knobs on the master control: Drive and Tone. That’s essentially all that defines the subtle sound being added to your tracks.
To restate an earlier point, HEAT can only be applied to Audio Tracks – not Auxes, Master Faders or MIDI/Instrument tracks. HEAT is inserted either pre or post inserts onto your audio being played off your hard drives. Consequently, it can’t be used on aux sub masters etc. Apparently, Avid chose not to implement it on other ProTools tracks to minimise the chance of double processing and eating up DSP.
The Drive and Tone master controls are hidden by default, and revealed on the right-hand side of the Mix window in much the same way as the Track and Group lists are on the left. The controls default to 12 o’clock on the pot – ‘midday’ is neutral: nothing added. From there you can take five steps in either direction on the Drive pot and three either way on the Tone pot. Turning the Drive to the left adds Tape saturation modelling: warmth, odd-harmonic excitement in increasing levels as you approach the fifth most extreme setting. Turning it to the right gives you tape saturation in addition to further tube saturation modelling, adding both odd and even harmonic excitement that produces a crunchier, livelier, gutsier feel as you crank it all the way. This can cause the loss of perceptual top end on the tape side, as might occur on a real tape machine at extreme level settings, and this can be compensated for with the Tone control if you need to brighten things up a little. Conversely, too much tube goodness can make for a crunchy, bitey feel and you may find this tone needs to be backed off to soften the top end. Either way the Tone control is not simply an EQ-added post process or some sort of exciter. Rather, it inherently changes the character of the distortion model being used and consequently – as with the Drive control – your gain structure and frequency content will dictate the results on individual tracks.
SO HOW DOES IT SOUND?
First impressions: warm and gooey on the ‘Tape’ side; crunchy on the ‘Tube’ side. But again, it all comes down to gain structure and the nature of your recordings. Like real analogue circuitry, the outcome isn’t completely predictable and getting the sound you want involves trial and error, listening and experimentation. I’ve tried adding HEAT to existing mixes with limited results, yet by contrast, turning it on and mixing with it from the get-go can produce totally different outcomes – gobsmacking, lovely, warm sounds… the top-end of the faders just seem to push against a molasses of goodness that you quickly miss when it’s bypassed.
The HEAT process defaults to post-fader mode, which tends to produce subtler results, particularly when various other dynamic controls have been applied to individual channels first. In Pre-fader mode, however, HEAT can be quite temperamental, as you might expect. Hitting it hard with dynamic, transient material yields almost instant, easily discernable distortion no matter how soft you
drive it.
THE HEAT IS ON
Acoustic piano and guitar seem to show HEAT at its best. The complex harmonic content of these instruments really allow the maths to highlight all those third-order harmonics. It’s not always obvious what’s going on until you bypass the effect and your mix drops back, sounding lifeless and flat by comparison – particularly in the low mids.
By its very nature, HEAT is designed to effect different sounds in different ways. There’s no simple description of what it will do to your music and craft. Yes it will add some ‘body’ in the low end but is that desirable? I’ve always been an advocate for the clarity of mixing ITB and my go-to plug-ins have always had that natural tendency (avoiding THD wherever possible) but I’ve got an album coming up that I cannot wait to start tracking and mixing with HEAT on the whole time. It sounds great to my ears.
HEAT is indeed something quite apart from everything else on the market. It’s subtle, it’s clearly been designed by David Hill with the workflow of mixing in mind, and once you start using it it’s doubtful you’ll want to bypass it. Unfortunately, the masses of LE and M-Powered users out there may never get a chance to fall in love with it due to its proprietary HD 48-bit DSP architecture. According to Avid there are no plans for it to be made available to LE users any time soon, but whether that will change in the future only time will tell. As an LE user at home, and an HD user at work, I do miss it after hours but – and at the risk of putting some people offside here – as an HD facility owner I’m gratified to have something unique to offer my clients. If you’re running a ProTools HD system, HEAT is definitely worth trying out for 30 days courtesy of the free trial at www.avid.com.
