Audio post

By and large, the mass re-equipping of suites, machine rooms and infrastructure that has accompanied the migration from SD to HD in most areas of post production would appear to have taken place down the corridor from the dubbing theatres and tracklay suites of audio post production.

This is due in part due to industry standards and practices. Video’s “Content Acquisition Technology for HDTV” is still audio’s “Microphone,” after all. The 48kHz digital sample rates and 16-bit depths, the measures of quality and fidelity of audio that were well-established long before HDTV came along, are still standards today and are what you’ll find on the audio ins and outs on the back of a brand new HD deck. No new microphones, connectors or speakers required here. This is the key difference between the sea change of spec in video acquisition, editing and peripheral kit, and the lack of such in audio.

That’s not to say these standards won’t change. Sure, they’re convenient, good enough and offer better-than-CD-quality sound, but for many people, standard-definition pictures were once considered good enough. Perhaps it’s not really the point when something better exists. For users of some DAW-based audio workstations, higher sample rates and bit depths are already supported, should they be needed. For those who have eschewed the traditional mixing console approach in favor of a control surface, a change in digital audio industry standards would make no real difference. For the most part, implementation is a simple matter of settings and templates.

HD drives creativity

However, the same factors that have driven the uptake of, and expenditure on, HD technology — with the additional budgets required by the production companies to shoot and post HD — have affected audio post in a very different, and largely creative, way.

The same program-makers who want the quality and commercial longevity afforded to their content by shooting and posting in HD will typically also want to work in 5.1 surround for the same reasons. Broadcasters want (and need) to deliver surround to the hungry, increasingly informed consumers, most of whom know they can buy a basic five-speaker-and-sub set up in their local supermarket, often regardless of whether they are inclined or able to splash out on a new high-definition TV set to match — at least not until that 42in LCD comes down in price.

HDTV, more than anything else, means surround mixing and delivery in the context of audio post. Working in surround brings with it several technical and creative considerations, with the former now in much sharper focus than had previously been the case.

Equipping a suite with the requisite number of speakers and adequate routing and metering to manage the extra channels required to work in surround (on a simplistic level, granted) was never really the difficult bit. What to do with the mix once it was done was typically the technical bone of contention.

The generally preferred solution was not to concern oneself in post with the ultimate destination, if possible. Lay off, say, the six separate tracks of a 5.1 mix onto a digital, multichannel, time code-equipped tape format, being sure to label said tape inlay with the channel order and reference levels being used. (Felt-tip metadata from the old school.)

Eight into two

However, the impending demise of multichannel digital tape formats ultimately will rule out that approach. A rudimentary grasp of arithmetic tells us that six AES channels into four on a trusty Digital Betacam, or two on a DAT or satellite feed, just won’t go.

Meanwhile, the standards battle for end-user 5.1 surround formats rages on, with DTS, Dolby Digital and Dolby ProLogic all looking for market share, and ostensibly all suited to different media. Studio time spent creating, encoding and delivering a mix for each possible eventuality, network, territory and medium simply isn’t practical, or client-economical, for the majority of productions in post.

Here to address both these problems for audio post in surround (that is HDTV) is Dolby E. Increasingly, broadcasters are demanding that facilities deliver programs with Dolby E audio. This seemingly represents a win-win. Equipped with the requisite Dolby E encoder, decoder and metadata management technology at both ends, the 5.1 surround mix can be packaged, labeled with metadata, shrink-wrapped and delivered (alongside the stereo or ProLogic version) as a synchronous AES pair on any of the standard tape formats and infrastructures we know and love, SD or HD. For the dubbing mixer and facilities house, your job is done.

The master tape (complete with surround mix encoded as Dolby E) can be copied several times and even edited (for different commercial breaks for example) on its journey. It’s then up to the network, playout center or DVD authoring house what they want to do, and in surround format, with the multichannel audio they have extrapolated, with metadata, from the Dolby E bitstream. Should that decision change next year, no problem. The Dolby E stream will still be there to refer back to.

Over the past couple of years, the majority of audio post facilities have been gearing up for surround and indeed Dolby E with a minimum of fuss or fanfare.

Mixing surround sound

From a creative standpoint, mixing in surround is an evolving art. Several schools of thought, and myriad rules-of-thumb with regard to panning, folding down to stereo and use of LFE exist, depending on the genre, the material in question and its ultimate destination.

In many ways, parallels can be drawn with the experimental early use of stereo. Recommended listening to illustrate this point would be mid to late 1960s Motown. You’ll notice oddities like drums being mostly way out to the right and guitars to the left.

Early surround mixing sometimes followed a similar path. Now, with all the gimmicks and extraneous 360- degree circling long-since exhausted, the art is very much finding its way and adding real production value, subtle or obvious, commercial or artistic, in much the same way as HD pictures.

Given that soon, stereo programs scheduled in among surround advertisements, promos, idents, trailers and drama will both disappoint consumers (and, therefore, advertisers) and stick out like a sore thumb; the enigma for many directors and dubbing mixers now seems to be not so much whether to do surround for an HD production, but what to do with the surround channels at their disposal.

Advertisements and idents with complex sound design, plus feature films, sport and drama all naturally lend themselves to the use of ambient effects and low frequency rumbles, but what about reality TV? Certainly, the dubbing mixer, if pushed, can find something to occupy the rear speakers and low frequency channel, but if the program material isn’t suitable, then we’re in danger of regressing to the style of late ’60s Motown.

Production planning

Decisions made early in production about camera placement and moves (or, ideally, lack of them) have an obvious bearing on whether or not the resultant scene will be conducive to being recorded and mixed in surround. All of which suggests that the impact of HDTV on audio post-production permeates right back to the storyboard. Put another way, what is the impact of wanting to finish the audio with a surround mix on the production itself? Dubbing mixers I know are making a point of discussing their clients’ needs and expectations as early as possible in the process.

From a commercial point of view, signs are fairly encouraging for the facilities companies. From an impromptu straw poll, it seems that the budgets are there to spend more on doing a surround mix. After all, it takes more time — quite often a lot more time — and requires technology and skills investments on the part of the facility.

Surround mixing takes longer

While the hourly rate card may not always bear a substantial upwards hike for working in surround, the need to book more time seems to be readily understood — another key difference between the worlds of HD in the video world and surround audio in facilities. HD video editing takes essentially the same time, but the HD-equipped edit suite is typically more expensive per hour.

However, it’s by no means a given. Those dubbing mixers I know who were around at the time tell me that no such provision was made when, for example, the change from mono to stereo broadcasting happened in the ’80s.


The tracklayers and dubbing mixers are ready, able and enthusiastic about creating surround content for SD and HD TV. Just as well because consumers want to hear it (even if one of their rear speakers is tastefully tucked under the sofa and the other behind the fish tank). For my part, I’m hoping I don’t get asked in a year’s time to write a piece on surround audio for 3G mobile content. As they say in Motown, that’s a whole ’nother thing.

Ben Nemes heads Scrub, HHB’s specialist audio post-production division in London.