Could we do a horror on radio? Could we horrify people? Not an atmospheric, gothic spook with resonant chords and the whiff of damp tweed, but something actually scary. Something to make the audience squelch. That was the ambition.

There's a mantra in Hollywood that to be effective, a screenplay has to make your organs squelch three times while reading it. For organs read tear ducts, stomach, heart, bowels, the skin on the back of your neck, throat, toes... whatever. Are you literally physically moved by the writing? And if not, it's not ready.

Reading the final script of We Outnumber You (Friday Play, 2100 23 April) gave me a rare workout in squelching. It also reads like a list of fantastic challenges. Here are just a few, and how we achieved them.

A man, wearing a microphone, walks into a jackal enclosure at the zoo, and is attacked, killed and eaten by jackals, while an attendant crowd take pictures. Layer upon layer of sound went into this. The actor, Luke Treadaway, played it for real on his own in studio. The spot studio manager (who helps us record live effects), simultaneously chomped down on some melon very close to another mic. Separately we recorded the crowd, first screaming then stunned. We begged recordings of jackals off the Natural History Unit in Bristol, which we layered into the sound picture, together with some dog, and then degraded the whole edit to give the effect of a mashed up piece of equipment. All this work, and then the truly effective moment comes during the silence after the microphone goes dead.

A stampede of hippos that run down a crowd of visitors. Agitated hippos faithfully recorded sound remarkably - and disappointingly - like Denis Healey laughing, so that was out. However, we did find that hippos on tarmac sound very like horses on turf, slowed down, and pitch-changed, with added grunting from a mix of bear, pig and lion. And the actors did the rest, some of them running away, three of them staying and being crushed and one, the character whose foot is bitten off, holding the microphone.

A helicopter issuing a live news report crashes into an enormous bird sanctuary. Michael Shelford, the actor playing the reporter inside the helicopter, had to imagine the level of sound he was working against, and yelled his lines into the microphone. Behind him, we used the effect of a functioning light helicopter, which we then mixed with tearing metal, and a malfunctioning washing machine, and added an alarm clock (persistently and gratuitously warning the occupants something might have gone wrong). As the helicopter crashes through the enormous aviary cage, more metal tears, branches crack, wings flurry, and a cacophony of panicked bird cries add to the chaos, gradually trailing off as they all fly free, leaving only the burning of the wreckage.

A camera, set to record, is dropped fifty metres through foliage. The spot studio manager took a deep breath and blew steadily onto the mic, which after 'freefalling' for a second or two, was then hit from both sides by branches, before being dropped onto the ground, during which activity the actor - Ben Crowe - retreated silently to the other end of the studio sound trap so that his next line could sound fifty metres away.

And the hardest of all - a group of primary school children are crying. Weirdly the hardest sound to get right. It's easy to imagine children crying for attention, or crying with pain, but crying together from fear is so difficult to put your finger on. There are some stored recordings of children crying, little electronic pockets of misery on a hard drive, but they're the tears of children whose parents appear to be recording them when they should be comforting them, and not quite right. The Stalisfield Youth Theatre, in Kent, offered to cry for us. And scream. And stampede. And imitate monkeys. They were so great at screaming. Brilliant at stampeding past the microphone in mock panic. Hilarious monkey impersonators. But it took thirty attempts to get them crying right. Take after take foundered on 'boo-hoo'ing, on over-sniffing, on wailing, but mainly on giggling, and with each attempt the children became more and more miserable, understandably. And by the time they went home, they were utterly disconsolate.

So. We hope you squelch.

Jessica Dromgoole is Director of We Outnumber You

• We Outnumber You is on BBC Radio 4 at 2100 tonight (23 April 2010).
• Picture by Bartek Kucharczyk. Used under licence.

Right from the start it was clear that the sound of water would feature heavily in the soundscape of the production - the river Thames could be considered the central character of the piece as so much of the story is woven in and around it. Drownings and near drownings, Lizzie Hexam and her father earning their living in a small boat on the Thames and the rain drenched streets of London meant that the sound of water would play a big part. One of the big differences between doing a production like this on the radio and on film is that, generally speaking, the actors stay a lot drier on radio. Having said that, on a number of occasions we set an actor in front of a washing up bowl full of water and asked them to plunge their head in and emerge, gasping for air as if with their last breath. Which, for some of the characters, it was.

For a fifteen minute episode we have half a day in the studio to record the actors and add a lot of the sound effects. The main assembly of the programme then takes place in the editing channel. In the editing process we use four different types of raw sound:

• The words spoken by the actors
• Sound effects recorded in the studio
• Sound effects from pre-recorded sound effects libraries
• Music

All of these can be manipulated in the editing process - precise editing to isolate the sections you want, adjusting volume levels, adding reverberation etc.

The scenes involving drownings are good examples of how the radio sound picture is built up using a number of different elements. The drownings all involved a struggle with two characters; so we would record the dialogue leading up to the struggle and the vocal sounds of the characters fighting and gasping for air. We might then record the sound of their feet, scuffing the pavement and some additional splashing. A lot of the picture would then come from pre-recorded sound effects - the background sound of the river flowing and the surrounding ambience, splashing and the sound of scuba breathing.

Creating the image of the characters going underwater needs precise placing of sound effects and acoustic treatment of the sound to paint the picture without the help of any dialogue to explain what is happening. A splash as they fall into the river, vocal struggling and splashing, followed by an isolated large breath from one of the characters. This breath subconsciously leads us to expect they are going underwater. As they go under, the bright sounds of the splashing are suddenly reduced in volume and the higher frequencies are taken out to give the murky, dull sounds you associate with being underwater. The scuba breathing gives us the rising bubbles and the classic underwater sound. A rasping breath signals their breaking of the surface, the volume of the splashing is increased and the high frequencies are brought back as they hit the night air. We would then add a track of Roger Goula's music, possibly adjusting some of the timing of the scene to fit the drama of the scene with the shape of the music.

I spoke to Roger about his music for Our Mutual Friend:

Colin Guthrie was sound designer for Our Mutual Friend

• Roger Goula writes music for film, television and radio. His personal web site is here.
• Radio 4's 20-part adaptation of Our Mutual Friend is on-air now.
• Radio 4's 20-part adaption of Our Mutual Friend is on-air now and because it's part of the 'series catch-up trial' you can listen online to all the programmes in the series until seven days after the last episode airs.
• We'd love to hear your thoughts about Dickens dramatisations you have heard and enjoyed on the radio. And which of the novels do you think Radio 4 should tackle next?
• There are production photos of the whole cast, taken for Radio 4 by Phil Fisk, here.

Only last week I was fretting about my return to work, after having had time off to have my second baby. But why should I worry? Of course I would remember how to sound-edit the programme, and I would never go into a blind panic when I had to point that microphone for the latest sound effect needed in studio! This week? I can honestly say that I feel as if I had never been away! And there really was no need to panic.

Coming back to work - even when what you do involves editing and microphones - is much like riding a bike - you rarely forget.

There is always so much to do in the run up to studio week, for me, so if I was going to pine too much after my adorable boy, and my hilarious daughter, then this was a good week to choose a return. I honestly haven't stopped.

I have already recorded on a beautiful farm in deepest Leicestershire (yoghurt-related effects) and I have had a good few children in to repeat lines after me. Then there is the hectic compiling of episodes, playing out (our speak for listening back to the final version), scheduling and podcasting.

Today, already, I have played out 6 episodes that transmit in a couple of weeks (not quite Christmas, but if I hear any more Christmas hits, I think my head may spin), planned a couple more recordings, done some episode scheduling and podcasting, and am just about to commandeer an edit suite to play out an Omnibus...

Then, when the day is done, and I can be sure that the listeners will get their daily dose of the programme, I will pop out for a good run (my other passion, besides my kids and my job), and then back home... but you don't want to know the trials and tribulations of that part of my day!

Sonja Cooper is a Technical Broadcast Assistant on The Archers and she's responsible for recording many of the sound effects you hear on the programme

• Here, for your listening pleasure, are some of the sounds captured by Sonja on her recent travels:

• Archers Week ran on the Radio 4 blog from 23-30 November 2009. 19 blog posts were published in all, from 17 authors. They're listed here.
• Radio 4's Archers web site is full of good stuff, like a map of Ambridge, family trees for all the big clans and a detailed who's who. There's also a 'two-minute guide' for Archers newbies.
• The Archers messageboards are among the busiest at the BBC - nicknamed Mustardland because of the distinctive yellow page backgrounds. They're a bit sceptical about Archers Week, though.
• There are two Archers podcasts: one for the daily episodes and one for the Sunday omnibus.
• Hedli Niklaus, who plays Kathy Perks in the serial, also runs the Archers fan club, Archers Addicts.
• Norman Painting, who played Archers patriarch Phil for nearly sixty years, died on 29 October 2009. The last episode he recorded aired on 22 November. Archers Editor Vanessa Whitburn paid tribute to him here on the blog and the Archers Addicts have collected listener tributes.
• During our visit to the Archers' home in Birmingham dozens of photographs were taken, many of which feature pictures of cast members (and an ironing board).
• Twitter was put to use during Archers Week. #archersweek was the hashtag and we learnt that Tim Bentinck, who plays David Archer (@timbentinck) and Keri Davies, who writes scripts (@keridavies) are both Twitterers. Follow the Radio 4 blog on Twitter.