Encapsulating over half a century of theatrical history, Agatha Christie's The Mousetrap is the world's longest running show. First performed in 1952, the whodunit drama is about to begin its 60th year and has clocked up over 24,500 performances, with more than half of these in the show's current venue – St. Martin's Theatre, London.

Given the show's record-breaking run, its producers strive to keep a balance between preserving its charm – and undoubtedly successful formula – and ensuring the performances stay fresh. To this end, the current production was re-launched with a new cast during October 2011. As part of this most recent evolvement, it was felt high time to rethink the show's sound design, particularly to update the sound effects replay technology, as well as recreate many of the effects themselves, some of which dated back to the show's earliest days. Andrew Mills, General Manager and Denise Silvey, Production Supervisor for The Mousetrap, sought Orbital's advice, resulting in Richard Carter taking on the role of sound designer, and specifying a CSC Show Control system to replace the production's occasionally misbehaving CD player, and provide much improved ease of use and flexibility. Richard also spent many hours in Orbital's studio, cleaning most of the older effects and creating others from scratch, to generate over 70 refreshed cues.

Denise Silvey, Production Supervisor for The Mousetrap, explained:
"We are very proud of the show's heritage, and are naturally cautious about making any changes to the production - we're reluctant to alter anything purely for the sake of it, but we are also keen to keep the show fresh and ensure its continuing appeal. The production's sound effects were long overdue for improvement - they needed to sound as crisp and clear as possible - and, due to our long-standing relationship with Orbital, it was natural to approach them for help. Richard did a fantastic job, cleaning up the old effects and adding a lot of new ones, and they now all sound wonderful and fresh.

"I was first involved with The Moustrap in 1994, when the show was still using reel to reel tape for replaying the effects. Splicing tape was the order of the day if you wanted anything changed! Some of the effects date from a long while ago - the voice of the announcer for example, is that of actor Deryck Guyler. The recording was made in 1952, long before noise reduction was available for tape! Richard has performed miracles for us, cleaning up and restoring some of these older effects. In the show's earliest days, a lot of the effects were purely mechanical, and we're very proud of our hand-operated wind machine, which is still used every night - it's become part of the show's heritage. And the mantelpiece clock, which is the same one used in the very first production, now has a sound of its own for the very first time - but this is made by the stage manager hitting a triangle, so we have still kept some things mechanical!"

Progressing from the purely mechanical, some effects migrated onto record to join the Deryck Guyler recording, although given the very small quantities of discs required, these would have been direct-cut acetates to avoid the expense of pressing on vinyl. During the show, the success of an individual effect would have depended on the operator dropping the stylus onto the record at exactly the right cue point. The process would have been prone to inadvertent timing errors, with the added issue of surface noise heralding the imminent start of a sound effect!

The commercial availability of tape recorders eventually introduced a further degree of sophistication in the early 1970s, as at least the show's effects could benefit from the improved runtime of a reel of tape, with the cueing, starting and stopping of an effect simplifying the task compared to records. Tape hiss added its own problems though, and the next step was to migrate the effects onto CD, once economical and accessible CD-Rom production became available.

So from their days on reel-to-reel, and until the changes this autumn, the show's sound effect cues have been running on a CD player, with the target replay levels of the various effects marked on strips of masking tape arrayed around an amplifier's gain pot. A simple and reasonably effective method, but obviously capable of improvement.

Orbital's Richard Carter picks up the story:
"There were two principal issues to address - the effects' replay chain, and the quality of the effects themselves. We addressed the first issue by upgrading the CD-based hardware to a CSC v3 Show Control software system running on a PC, linked to a Yamaha 01V96 digital mixer and four Yamaha power amps. Migrating to CSC has at last enabled sounds to be layered, whereas the show was previously limited to one cue at a time. We installed dual screens for the CSC - one beside the system and one at the prompt corner. The DSM has a very simple control box for the sound effects, with just Go, Stop, Next and Previous buttons. With the new hardware, updates are now very easy to do, by connecting a laptop out in the auditorium back to the system via a Cat5 cable. You can now run through any changes, updating on the fly until the director is happy. We have retained the theatre's existing effects-replay loudspeakers, but relocated some speakers out of the pit, and moved them higher up to give much better coverage of the auditorium. Essentially, we released some loudspeakers that had previously only been used for announcements (as this had its own, independent system), enabling more effective re-distribution. The improvements were instantly audible.

"The next stage was to evaluate the effects and start to make whatever improvements we could. I received all the effects on CD, and auditioned them all in detail. There were a lot of pops and clicks that needed cleaning up, some tape hiss was apparent – peculiarly more so on the right hand channel - as well as several instances of original vinyl surface noise. I spent a long time de-noising and re-EQing to brighten up some effects, and applied a variety of de-clicking and de-popping algorithms, auditioning these until I'd achieved the best possible fit. The target was to reach the optimum compromise between minimum noise and top-end accuracy. All the effects were in mono, so they were re-processed with a touch of reverb and stereo widening algorithms to generate a larger sound field. One music cue even had a glitch right over an obvious flute solo, presumably due to a tape dropout, but we managed to ‘micro-edit' it at sample level, and restored the cue to its original state - but now rather cleaner-sounding. We also restored all the other music cues."

With the show's new director, Geoff Bullen, in place for the October re-opening, some new music was requested, and these cues were incorporated into Richard's new sound design, as well 25 new wind cues that augment the hard-driven wind machine. The new cues contribute to the show's eerie atmosphere, and although are often run at a very low level, they help to make it as involving and convincing as possible. As part of the new wind cues, Richard used layers of wind effects looping at offset intervals, which are brought in and out as required to form an ever-changing background. Period correctness is an important part of the show's ambience, from the sound of a 1952 telephone ringing, to the appropriate behaviour of cues that appear to be delivered by a large wooden valve radio - its speakers are behind an adjacent scenery flat.

"Getting these cues correct was an interesting part of the project," continued Richard, "recreating the effect of the radio's valves warming up, to make the radio system sound as authentic as possible. Around 10 radio cues were needed, and they ramp up, initially rather muffled, and then getting clearer as the valves come to life. We had to guess though as no one I spoke to could remember exactly how they used to sound! There are some points in the play where the radio is retuned on stage, and we added a "radio tuning swoosh", followed by a crackling sound, and then the cue is heard gradually clearer until the clean signal is found. And so while we spent many hours cleaning up the other effects, we had to make the radio cues deliberately noisy in places!"


Richard played the piano on one cue, where a piano is heared distant and muffled off-stage, but then clearer when a door is opened. The piece was played with one finger, recreating some mistakes that synchronise with the on-stage action. The show has retained a few manually-operated mechanical effects, including the wind machine, the chiming clock, and a crackling fire created by scrunching gel. An early 1950s Electrolux vacuum cleaner also plays itself in the production!

Richard Carter summarised the sound effects work:
"In total, the show now has just over 70 separate sound cues, requiring an substantial amount of studio time, with many of them created afresh for the show's October reopening. There is a new opening sequence, new music, and new soundscapes at intervals throughout the production. There is also now more movement to the sound, especially between the radio and proscenium systems, that adds to the tension and drama of the play. Added togther, this most recent round of updates to The Mousetrap makes it even more a quality West End show - still in sympathy with the period character and tradition of the production, but now capable of delivering world-class West End quality at the points that matter."

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"The production's sound effects were long overdue for improvement - they needed to sound as crisp and clear as possible - and, due to our long-standing relationship with Orbital, it was natural to approach them for help."