In October of last year, BBC Wales introduced a new TV series entitled Torchwood, a spin-off of the latest (and wildly popular) Doctor Who series. The storyline of Torchwood centers on a secret organization, the Torchwood Institute, which solves crimes using alien technology. Because the show is produced internally by BBC Wales alongside Doctor Who as well as a second spin-off, The Sarah Jane Adventures, production demands are immense. For the three shows, a single crew produces nearly 40 episodes that involve unique sets, intense stunts, and CGI effects.

“The time constraints are huge,” says Tim Ricketts, Dubbing Mixer for the series, “so it’s pretty much a case of the first take being the rehearsal for the sound recordist. After that, it’s a case of ‘sort it out in post’ if it all goes wrong!”

In order to successfully capture as much dialogue on the set as possible, the audio team uses a Zaxcom Deva hard-disk recorder with timecode synchronized to that of the camera. The team then feeds one or two boom mics, four radio mics, and up to two spot mics into the Deva. The feeds are also sent to a small location mixer, which provides a rough audio track for editing purposes.

Back in the studio, the Deva audio is saved as Digidesign^® Pro Tools^® tracks and then synchronized with the edited show. Dialogue editors can pick from the eight audio channels to produce the dialogue edit. Once the edit is analyzed for gaps in the recorded dialogue, cast members are brought in for ADR sessions and all dialogue is finalized. The completed dialogue edit is then sent as a collection of eight tracks for the main mixing session.

The BBC Wales team uses an AMS Neve DFC Gemini mixing desk, which is capable of mixing 5.1 audio with multiple stems. The tracks are played directly from Pro Tools into the dubbing suite, which has the capability to support up to 112 tracks via MADI. These tracks are arranged into a standard template developed to speed up the mixing process. Ricketts mixes these into five stems: dialogue, music, spot effects, Foley, and background atmospheres.

While Torchwood is filmed in high definition and is produced with a 5.1 soundtrack, the vast majority of BBC viewers will currently be able to see the show only in SD and stereo, due to limitations with the current BBC transmission path. Because of this, the primary mix is a stereo soundtrack derived from the 5.1 mix and encoded in Dolby^® Pro Logic^® II.

“I use a Dolby DP563 Surround and Pro Logic II Encoder to produce Pro Logic II from the desk’s 5.1 output,” explains Ricketts. “A Dolby DP570 Multichannel Audio Tool is fed the same 5.1 output.” The Lt/Rt outputs from the DP563 are routed into the DP570 so that Ricketts can monitor the Dolby Pro Logic II production directly, his preferred listening mode. “By remotely controlling the DP570 via a PC in the dubbing suite,” he says, “I’m able to listen to any mode quickly, whether it’s full 5.1, Dolby Pro Logic II, stereo, or mono.”

Ricketts prefers to start his mix with the dialogue tracks, the only part of the audio that may have been premixed as it was produced. “All the mixing is virtual,” he explains. “Nothing is mixed as a stem to tape or Pro Tools. The dialogue is premixed to some extent in Pro Tools, but the final tweaks and compression is always done on the DFC.”

After the dialogue, Ricketts adds the Foley, then the atmosphere tracks, and finally the music and spot effects. He does this primarily to ensure the dialogue is clear, and also to maximize the effect of the audio in each scene. Ricketts explains that with Torchwood, “The viewer isn’t just looking at the scene, they’re in the scene—it’s all around them, especially the interiors. The mixes I create have the full Dolby Digital dynamic; a gunshot is explosive, and not just a pop. You can literally make the viewer jump, something you can’t do with a stereo TV mix.”

To produce a mix with this level of attention to detail is not a quick job. Ricketts is constantly adjusting the dialogue, Foley effects, and background elements of the mix as he builds it, creatively building a cohesive audio image that involves the viewer and draws them into the onscreen drama. He also holds back on his use of surround effects, ensuring maximum effectiveness when surround audio is employed.

To avoid issues associated with headroom limitations, Ricketts foregoes use of the LFE channel for the Dolby Pro Logic II mix. For the 5.1 digital mix, which has no such restrictions, Ricketts lowers the dialogue level to increase the headroom for action sequences, moves some of the effects audio to the LFE channel, and spreads the music around for a better effect.

This 5.1 mix is then recorded to Tascam^® DA98 tape for layback onto the HD master. By moving the 5.1 mix to separate tape, it is easier to offset the audio by the one frame required by the DP571 Dolby E Encoder to produce the Dolby E track. The Dolby E track is laid back onto tracks 3 and 4 on the HDCAM tape for transmission.

Designing the show for 5.1 audio from the start made things easy for the production team. As Ricketts explains, “We’ve been involved with 5.1 since 1996, and made the transition to Dolby E three years ago, so we’ve built up some level of experience. It is actually very easy to mix in 5.1, listen in Dolby Pro Logic II, and generate two mixes for essentially for the price of one.”

And they don’t intend resting on their laurels. “I think that, for the second series of Torchwood episodes, we will increase the track count to be able to make the effects more exciting. We are also keen to record and mix the music in 5.1.” (It is currently mixed in stereo.)

Episodes of Torchwood have taken 9 out of the top 15 places in the ratings charts for BBC3, and the show has an average four million viewers per episode across both digital BBC3 and analog BBC2 (where it is repeated). It is clear that the BBC Wales team have another major hit on their hands and are going to be busy for the foreseeable future. With their commitment to creating involving soundtracks, and their desire to improve and expand their experience, it is clear that they will continue to treat viewers to top-notch science fiction and an increasingly engaging audio experience.

See A Guide to Audio for HDTV in Europe for more information about the production, distribution, and transmission of 5.1-channel surround for HDTV broadcasts. For additional information about Torchwood, visit www.bbc.co.uk/torchwood/index_nonflash.shtml.