The audio experience in films has undergone a phenomenal transformation over the last century. In the earliest days of cinema, movies were silent, relying entirely on expressive visuals and live musicians or orchestras to communicate drama and emotion to audiences. With the introduction of synchronised sound – notably in The Jazz Singer (1927) – the industry witnessed a revolution, forever altering storytelling by giving voice to characters and offering directors new creative control over narrative depth. This transition brought along technological challenges, including sound recording and reproduction, as well as the need for theatres to upgrade their equipment.

However, following the advent of the talkies, the quality and artistry of sound recording became a well-defined and prominent area. Boom microphones, optical soundtracks, and an interest in diegetic sounds (sounds that originate from the film's world) began to enhance the quality of sound design significantly. The term soundscape entered the fabrication, with directors starting to construct a new space through ambient effects and off-screen sounds. The late 1970s saw the emergence of multi-channel stereo and surround sound productions that would become the standard industry formats. With these new environmental audio presentations, sounds became directional in a way that suggested to the viewer a greater degree of immersion than with sound equipment previously.

This article discusses the evolution of film sound technology over the years, explains what spatial audio is, and distinguishes it from Dolby Atmos, while also examining how Hollywood and Bollywood have adopted these technologies differently. There is also a reflection on landmark films that have transformed the sound landscape in cinema, as well as the current gap between Indian and Western cinema in terms of sound.

The Evolution of Film Audio: From Silence to Spatial Soundscapes
Cinema began without sound, with films accompanied by live music, either performed on stage by musicians for the audience or off stage in an orchestra pit. In these early films, visual images were used in conjunction with intertitles to tell their story. Still, the limitations of movie production were apparent; there were no synchronised sounds to express dialogue or other nuanced sounds.

The integration of sound with picture led to many experiments, including the Vitaphone system in the 1920s, which synchronised a phonograph record with film projection. Warner Bros. 2019 ‘Don Juan’ (1926) was produced with this system, allowing for music to accompany the film, but no spoken dialogue was included. The major milestone came with ‘The Jazz Singer’ (1927), which incorporated synchronised speech, songs, and other sound effects. It was the first real film to be considered a "talkie." This was a major paradigm shift that led to the widespread adoption of sound film technology throughout the entire motion picture industry by the 1930s, despite initial resistance and technical obstacles.

Throughout the following decades, sound quality and fidelity steadily improved. Mono sound transitioned to stereo sound, where separate left and right channels created a sense of directional sound effects. In the 1970s, Dolby Stereo became available with films like ‘Star Wars’ (1977), which established multi-channel surround sound for commercial cinema, allowing audiences to be enveloped with sound in panoramic experiences. In the following years, we progressed through advancements in sound technology, including Dolby Digital (AC-3), DTS, and ultimately Dolby Atmos, introduced in 2012. This technology added height channels overhead and utilised object-based audio, which positions sound in a three-dimensional space.

Each advancement opened the sonic palette, allowing audiences not only to hear, but to be aurally "placed" in the film space. Surround sound meant the audience was engulfed in sound, and today, spatial audio allows sound to come from around the audience and above, effectively recreating the mechanism by which sounds are perceived in the world.

Understanding Spatial Audio: A 250-Word Explanation in Simple Terms
Spatial audio is an advanced audio technology that enables sound to be experienced as if it emanates from a three-dimensional area surrounding the listener, rather than simply from left or right speakers. It emulates the manner in which humans naturally experience sound in the real world, encompassing multiple directions and distances, thereby establishing a more natural and lifelike audio experience.

Traditional stereo audio relies on two channels (left and right), which are limited to simulate the horizontal directional perspective of sound. Spatial audio permits additional depth (front-back) and height (up-down), allowing the listener to perceive a sound as coming from above, below, in front of, or behind, or to the sides of them.

Spatial audio utilises the audio technology known as Head-Related Transfer Function (HRTF). HRTF simulates how sound waves interact with a person's head, ears, and torso, thereby altering the sound the listener perceives slightly based on their position. These changes are imperceptible but are still subjective changes in the direction of the spatial sound, and are taken by the brain as signals to "locate" the sound source. For example, a bird chirps above your head. The brain takes these tiny differences in timing and loudness from the sound source and interprets the information to help the listener locate the bird in a precise 3D perspective.

Spatial audio is usually best experienced through headphones, which can replicate a complete 3D sound space by processing audio signals to simulate these natural acoustic cues. Programs such as films, music, and games that utilise spatial audio feel real because they reproduce this natural way of hearing. For example, in a film’s battle sequence, the arrows flying in from behind or footsteps from above can sound as if they are actually passing by the viewer.

Instead of traditional surround sound formats, spatial audio can adapt dynamically and provide a customised, encompassing soundfield that dramatically improves immersion and emotional connection.

Spatial Audio vs Dolby Atmos: Key Differences
While the terms "spatial audio" and "Dolby Atmos" are sometimes used interchangeably, they refer to related but distinct concepts in the field of immersive sound technology.

- Spatial Audio is a catch-all for several branches of 3D sound technologies that create an immersive sound field. It works by simulating sounds in a three-dimensional sound field via HRTFs and object-based audio, and is usually optimised for headphone listening. Spatial audio can also often be platform- and hardware-independent and can be utilised on a variety of devices, such as smartphones, headphones, and VR headsets.

- Dolby Atmos is a proprietary commercial immersive audio format developed by Dolby Laboratories. It builds on traditional surround sound by adding overhead speakers and object-based audio mixing. Atmos systems work by dynamically assigning "sound objects" to a 3-dimensional soundfield, and can be used in cinemas, home theatres, or certain headphones. Atmos requires specific hardware setups for the whole experience, with ceiling speakers being standard in theatres, although headphones can also be used to simulate height channels.

- OTT (over-the-top) streaming services, such as Netflix, designate these terms according to the audio format and delivery method. When you see the term "Dolby Atmos," it often indicates premium multi-speaker support that can deliver object-based audio in a theatre or at home on an Atmos-enabled setup. The term "Spatial Audio," especially when advertised using Apple devices and supported headphone formats, generally refers to the ability to provide 3D sound using head-tracking and HRTFs (head-related transfer functions) for a more personalised experience with headphones. It may also sound the same on some devices that do not use an Atmos speaker setup at all.

In summary, Dolby Atmos is a specific type of spatial audio technology with distinct hardware requirements. In contrast, spatial audio is an umbrella term encompassing various 3D sound technologies that enhance immersion in different contexts.

Hollywood’s Swift Technological Adoption vs Bollywood’s Gradual Transition
Hollywood studios quickly understood the potential of sound for storytelling and continued to invest heavily in audio technology. The transition from silent films to talkies was rapid in the U.S. as major studios shifted to synchronised sound in the early 1930s. In the decades after, Hollywood developed surround sound, Dolby systems, and subsequent immersive formats (e.g., Dolby Atmos).

The rapid adoption of these formats rested upon hefty budgets, engineering teams, sophisticated recording studios, and theatres specifically built or retrofitted for multi-channel audio. Hollywood studios often sought to impress audiences with extravagant audiovisual spectacles, rendering sound design an integral part of creative development.

In comparison, Bollywood (and Indian cinema overall) have taken longer to develop comparable audio sophistication. For a long time, much of Indian cinema relied on the censoring of audio dialogue by using the method called Automated dialogue Replacement (ADR), where actors would dub in their dialogue in post-production - typically in a studio that was not necessarily adjacent to the scene that was recorded. This led to some similarly problematic situations with naturalistic spatial audio, as sound and voice were not necessarily connected to the authentic acoustic effects of an environment.

This transformation of trajectory began with films like ‘Lagaan’ (2001). They were among the first to incorporate synchronised sound recording, using realistic on-location audio capture after decades primarily dominated by studio dubbing. However, for quite some time, Bollywood had not commonly adopted spatial or immersive audio technologies primarily due to budgetary constraints, a lack of trained sound speciality engineers in the industry, and students' tendency to focus mainly on songs and music rather than sound design.

While Hollywood regularly employs spatial and object-based sound solutions for greater immersive impact, Bollywood films are starting to catch up. However, they are still behind in terms of audio sophistication and infrastructure quality.

The Moment Sound Became Cinematic: Recognising the Power of Film Audio
As technology advanced, audiences' awareness of sound's economic value likewise evolved. For example, in the early years of sound film, the "wow" factor was synchronised dialogue. There are reports of pandemonium as early talkies began to synchronise an actor's voice and on-screen sound effects, which caused raucous excitement in the theatrical atmosphere.

By the 1970s, filmgoers began to notice that films like ‘Star Wars’ and ‘Apocalypse Now’ (with the advent of Dolby Stereo surround sound) expanded the sound space and increased the impact for viewers. Sound design became a significant component of discussions that critics and audiences began to notice and promote, as it could create moments of tension, excitement, or immersion for viewers.

Today, the audience has even higher expectations. We live in an era when audiences expect hyper-realistic audio landscapes, which provide a fully immersive experience in both cultural and cinematic contexts. Formats such as Dolby Atmos and spatial audio enable audio layering and placement, allowing every subtle element to crackle with almost tangible presence (such as rustling leaves overhead or distant sounds cutting through the vast silence). The audience perceives sound mixing as an essential part of the cinematic craft, and they recognise that a great sound mix significantly contributes to the emotional experience of film-going.

Today, streaming services have begun to offer audio in spatial or cinematic audio formats, indicating to the cultural consumer that audio technology enhances the overall home experience and places value on the audio expertise typically found in the cinema.

Hollywood vs Bollywood: Comparing Audio Technologies in Depth
Hollywood and Bollywood differ significantly in their use of audio technologies. Hollywood quickly adopts new technologies, easily transitioning from synchronised sound to Dolby Atmos. Bollywood, on the other hand, has been slower to adopt, taking decades to move away from relying on Automated Dialogue Replacement (ADR) and dubbing. Hollywood much prefers immersive and real-world-sounding environments, as well as subtler blends of ambience, whereas Bollywood focuses on clearly understanding dialogue and music, often sacrificing ambient textures. The larger budgets of Hollywood enable extensive post-production teams, advanced studio systems, and specialised theatres featuring systems like Dolby and THX.

In contrast, Bollywood's often limited budgets do not allow for extensive sound design or immersive theatres. While it is typical, Dolby Atmos and spatial audio are also mainstream in Hollywood's larger productions and are often supported through home theatres and streaming platforms. Bollywood, however, is still developing this technology, and immersion is still a relatively low number of films.

Location sound recording in Hollywood remains a common standard, with filmmakers seeking to maximise the chances of capturing spatial sound. Bollywood, meanwhile, incorporated ADR into its common films for decades, which meant the emphasis on audio was instead on the dialogue. Audience expectations demonstrate these patterns - typically, Hollywood audiences expect and experience enveloping audio, whereas Bollywood is more visually and musically focused, with a greater emphasis on emergent audio awareness.

The gap in sound sophistication between Hollywood and Bollywood stems from distinct production cultures, audio investment priorities, and differing audience expectations for audio content. Hollywood's massive productions focus on creating an all-encompassing audiovisual experience, whereas Bollywood has historically prioritised songs and star power over sound staging. However, Indian filmmakers are utilising new sound technology to a greater extent, and the higher sound requirements of online streaming are helping to bridge that gap.

Breakthrough Films Driving Audio Innovation

Hollywood Milestones

The Jazz Singer (1927)
The Jazz Singer was the first full-length film to feature synchronised pre-recorded music, in addition to sequences depicting lip-synchronous singing and speech, which contributed to the commercial rise of “talkies.” Released in 1927, it marked the end of the silent feature film era and transformed cinema by integrating sound and dialogue, fundamentally altering filmmaking and audience experiences worldwide and laying the groundwork for future sound films.

Star Wars (1977)
Star Wars was revolutionary in film sound by popularising multi-channel (multi-track) Dolby Stereo surround sound. This new audio technology expanded the soundscape of the cinema beyond mono (or stereo) sound recorded onto the same track, immersing audience members in a richer, directional audio experience. It drastically enhanced the narrative aspect and ambience of a feature film. It established a new set of industry standards for creating immersive audio in feature films that would become a staple of blockbuster filmmaking.

Jurassic Park (1993)
Jurassic Park was noteworthy as a revolutionary film, particularly known for being the first feature film to employ DTS (Digital Theatre Systems) digital surround sound. DTS technology provided crisp (high-quality) multi-channel digital audio that fully brought the film's dinosaur sound effects to life. This innovation significantly shifted audience expectations for sound quality and became the standard for digital audio in Hollywood studios producing motion picture films.

Gravity (2013)
Gravity used Dolby Atmos technology to create an immersive soundscape that replicated the emptiness of outer space. Atmos facilitated sounds to come from literally every direction, including above, and produced a very realistic vacuum sound field. This immersive approach to sound had a significant impact on the film's tension and realism, illustrating the extensive storytelling capabilities of object-based spatial audio.

Mad Max: Fury Road (2015)
Mad Max: Fury Road is renowned for its dynamic and innovative sound mixing, which seamlessly blends massive action sounds with rich environmental details. Its dynamic sound designs received a terrific amount of accolades and even awards. In effect, the film's sound played a crucial role in its visceral storytelling and impact.

These films significantly contributed to audience anticipation and raised the technical standards for immersive sound design in cinema.

Bollywood Milestones
Lagaan (2001)
Lagaan was an iconic Bollywood film, marking the first significant production after 30 years to extensively utilise synchronised location sound. Directed by Ashutosh Gowariker and produced by Aamir Khan, Lagaan was filmed using the Arri535 camera, which allowed diegetic dialogue and ambient sound to be captured on-set, creating greater audio authenticity than the prevailing mode of studio dubbing in Indian cinema.

Karuppu Roja (Tamil, 1996)
Karuppu Roja was one of the first films in India to adopt advanced audio technologies in the realm of the cinema by utilising the DTS surround format. This digital sound format enabled multi-channel audio streams, allowing for richer, more textured sound and providing surround sound effects. This marked an important step towards modernising sound practices in Indian film, while enhancing the cinematic audio experience over traditional stereo formats.

Judwaa (1997)
Judwaa also incorporated DTS surround sound technology into its production design, although it was not utilised to the same extent as in future productions. Nonetheless, the film was able to provide its audience with layered audio depth and spatial audio effects, suggesting that Bollywood's early experiments with immersive audio formats were successful. Although Judwaa did not offer a fully immersive audio experience, it introduced audiences to, and was aware of, multi-channel audio beyond the typical setup.

Vikram (2022)
Tamil film Vikram was recognised for its exceptional sound design and audio quality that coincided with that of leading film industries internationally. The film's soundscapes, precise mixing, and spatial sound enabled sound design to reach new heights in audio quality, confirming a higher understanding of sound production standards as a consequence of Tamil cinema's sound industry adapting its production format and standards. Vikram emerges as a unique example of the increasing level of commitment in Bollywood to some version of Hollywood soundcraft, and Vikram demonstrates Hollywood-level sound craft.

Jawan (2023)
Jawan leapt conventional discussions about the state of sound in Bollywood into lively debates, particularly regarding dubbing and the overall audio quality of synchronised sound recordings. The film employed various immersive sound techniques to underscore the significance of "live sync" sound recording in achieving authenticity. Those who have adopted mixed field recording in sound mixing, with implications for Bollywood's growing exploration and understanding of audio construction and sound design, have developed a greater confidence in using spatial audio in Bollywood to enhance narrative realism.

Though Bollywood took longer to embrace immersive audio technologies, these films represent crucial steps towards more complex and spatially accurate soundscapes in Indian cinema.

The Takeaway
Audio technology is advancing rapidly, and spatial audio is becoming mainstream. As headphones and devices capable of spatial audio become more readily available, streaming platforms are integrating spatial features into their offerings, and audiences are appreciating immersive sound experiences. Sophisticated tools, such as Head-Related Transfer Functions (HRTF), further personalise the experience based on each person's ear shape, improving realism. Additionally, spatial audio will be combined with emerging technologies, such as virtual and augmented reality, to create more dynamic and interactive listening sessions, thereby enabling greater sensory immersion for audience members.

Indian cinema is poised to undergo a significant shift in audio technology. With new sources of investment and a growing interest in authentic sound design, Indian filmmakers aim to reach parity with international standards. As the audience continues to demand richer and more immersive sound experiences, sound innovation will become an essential part of enriching the storytelling process. The merger of traditional filmmaking practices with advanced spatial audio technologies will enhance the sensory magic of cinema, making sound an even greater co-creative force in the future of Indian cinema, and potentially in cinema worldwide.