When Feras Fayyad was put in prison for daring to document the atrocities visited upon his home country of Syria, he experienced all kinds of physical torture himself, yet what he can remember most about the experience is hearing the screams of women from other rooms, enduring pain he couldn’t even imagine even when he was in the same situation since he knew they were considered inferior within the patriarchal society. The sound has never left him, which is perhaps why it was destined to become such a crucial component of “The Cave,” his gripping follow-up to the Oscar-nominates “Last Men in Aleppo,” which testifies to the strength of the women who remain in the country to carry on the righteous fight, profiling Dr. Amani Ballour, a fearless female physician who helps to run an underground hospital that tends to the hundreds of thousands that have lost all remnants of civilization.

With the civil war raging on, Fayyad had limited access to the hospital, sending in a team of cinematographers to capture the chaos inside the hospital where the staff constantly rattled by the bombs above ground and making do with the precious few resources at their disposal, but he knew to place himself fully — along with an audience — at the side of Dr. Amani, he would need to take full advantage of what could be achieved on the other half of the cinematic equation, bringing in the Danish sound designer Peter Albrechtsen, who has elevated such recent nonfiction films such as “The Last Race” and “The Distant Barking of Dogs” into truly immersive experiences. Over the course of 18 months, Fayyad and Albrechtsen worked on getting every sonic nuance of the underground hospital exactly right, from the trembling metallic medical trays to the loose dirt shifting around the makeshift emergency room, with “The Cave” becoming the rare documentary to be mixed in cutting edge Dolby Atmos surround sound, while taking great pains to make the emotional experience equally acute as Dr. Amani shares her private thoughts and fears intimately with a voiceover.

As “The Cave” continues to travel the world following its premiere earlier this fall at the Toronto Film Festival, Albrechtsen spoke about harvesting such a rich cinematic experience from such limited resources of his own when no proper sound equipment could be used in filming at such a sensitive facility, building a team internationally to get the best results and the ethics of recreating an environment in a nonfiction film.

Given the nature of how this had to be filmed, it probably wasn’t the most sophisticated equipment to capture the sound to begin with – what kind of materials were you working with?

The production sound was very rough because it was recorded on the cameras of the photographers, who did a really great job, but they were under immense pressure, so the equipment wasn’t the best for the sound. It took a lot of cleaning up of the recordings to make the dialogue work in the cinema and then on top of that, Feras really wanted it to be an experience where you were enveloped by the environment of the cave, so we spent a lot of time gathering sounds, all the way from the sounds of these Russian jets to the sounds of the machinery at the hospital to the sounds of the stretchers being rolled through the hallways and the sounds of war in the streets – to build up a realistic environment. Just a month ago, Samaher, one of the main characters of the film, saw the film and she told Feras that this really sounded like it sounds in the cave, and for us, that was such a compliment because we worked so hard on the very physical, visceral experience of being in this hospital.

When working with sound in that way, are there certain ethics involved in terms of being authentic to the circumstances in a documentary?

I spend a lot of time on researching and finding the right sounds. For example, the actual Russian fighter planes in the film are the sounds of those [that were flying overhead] and when you are on location and recording, the sound is often very rough, so if you want to have a very visceral sonic experience, you need to gather sounds to create that. What I find is very important to get ahold of the sounds that are emotionally authentic. It has to be the right kind of hospital machinery, the right kind of planes, the right kind of weapons in the streets and so on, so we spent a lot of time researching and making sure that everything feels right. Feras is extremely sensitive to sound and really goes into every detail, so for example, he knew the sound of the shoes for Amani, our main character, had to have a special sound, so in that sense making sounds for a documentary, it’s very important to stay true to the environment, to the characters.

I know Feras had wanted a very immersive experience from the start. What was it like getting that surround quality with the Dolby Atmos?

It was quite amazing that the first meeting I had with Feras, he knew he wanted to work in Dolby Atmos and he had all these specific ideas for the sound that when you hear the film now, it is actually very much like he talked about from that first meeting 18 months earlier. Dolby Atmos is an amazing sound system that’s so enveloping with speakers all around you and a lot of people think it’s only for big Hollywood blockbusters with a lot of explosions and superheroes, but it sounds so natural the way it envelops you. For a film like “The Cave,” it was really great because it really made you feel like you were there, both in the quiet moments, but also of course in the moments where you can hear the war going on above you.

I was so fond of your work on “Distant Barking of Dogs” as well and I felt it was a similar challenge here, conveying the presence of a war you don’t necessarily see. Did you work there inform what you did here?

“The Distant Barking of Dogs” is also a very emotional film about war, but like it says in the title, the war is a bit more distant whereas “The Cave” is in the actual war zone – there are really several scenes you are in the middle of the war, and it’s very intense and it’s very physical. But the reason that both films are very emotional as well as [being] very dynamic pieces of filmmaking is that they have these very intense, very violent and very loud parts, but also moments that are very fragile and quiet and subtle, and I really like that dynamic. That’s a big part of the emotional effect of the film.

What was it like to build a team for this? You’ve said there were people from 12 different countries on the sound crew.

For me, it was a way of handpicking all the right people for a job like this. It’s really a soundtrack that could only be made now because nowadays you can send files back and forth on servers and communicate with Skype and Messenger and WhatsApp, so I had a sound effects editor in Beirut, the dialogue editor was in Berlin, the other dialogue editor was in Sweden, a Foley artist in Finland, a music editor in England, and we did some voice recordings with a Turkish sound crew in Istanbul. Tim Nielsen from Skywalker Sound from the U.S. did the very final mixing, so it was all over the world. That meant that we got a lot of very inspiring input and it was a really wonderful collaboration, but it was also a way of enhancing this feeling that the film is about Syria, but it’s also about humanity and how terrible war is, no matter where it is in the world. It was important for Feras that it both felt like a document of its time but also a timeless cinematic experience. By having this really wonderful sound crew, we gathered so many amazing sounds from around the globe.

I was also intrigued to hear that you worked with the music department and gave them a suite of sound effects to draw on for the score. What was that collaboration like?

The composer Matthew Herbert has done some wonderful electronic records and he’s really into playing around with sound just as much as with instruments and music and one of the first things he asked me to do was send a lot of the different sounds that I had gathered for the sound design because he really wanted that as an inspiration. Then in the music, he ended up using the elements from some of these sounds so when you hear the score in the film, it is quite classic in a way – and there a lot of classical instruments, but it has this extra sonic dimension. A lot of those sounds are manipulations of sound effect recordings that he got from me, so there was a really interesting interplay between sound and music in the film.

Was there a moment for you that was particularly exciting to work on?

There were several scenes which were difficult to do emotionally. It was really important to build something with the sound that created both the intensity and the emotional power of these sequences like the chemical attack, but there are several sequences Feras really built for sound, so one that I really like is a scene with one of the traumatized nurses who is sitting in a hospital room and it feels like she is listening to herself and the camera is just there looking at her. The sounds tell the story of what she’s thinking, and doing something that bold and brave is something Feras was great at.

What was this like seeing this for the first time?

It was so moving seeing this film with an audience, hearing how people were becoming very emotional. It’s something that we worked on for such a long time, and it would be wrong to say it feels good to be in a cinema watching this with an audience, but it feels very, very true to the spirit of the film that people have this emotional reaction. When I see it, I also get moved by it, even though I’ve seen it hundreds of times now. It’s such an intense film and of course, a tough one to work on, but it’s also a film that I’m very proud of what we created.

“The Cave” is now open in limited release. A full list of theaters and dates is here.