Surround sound has a long history, and the formats we enjoy today owe a lot to the technological developments and innovations of the past. In this article we take a look at some of the most notable formats of days gone by and consider how they helped to influence the surround sound formats we work with and listen to today. This won’t be an exhaustive list of every single surround sound format ever conceived, but rather a trip into some of the key formats and associated technologies which paved the way for what was to follow.

Fantasound

The first cinematic use of surround sound technology can be traced all the way back to 1940 in a system developed for Disney’s Fantasia. The orchestral score in the film was conducted by Leopold Stokowski, and Walt Disney tasked his engineers to develop a system which would be able to reproduce the music with the normal volume range and acoustic output of a full symphony orchestra. 33 microphones were used to capture the orchestra, with submixes of various sections of the orchestra being recorded to eight optical audio tracks. A ninth track was used for a click track to help the animators time their drawings to the music.

One of the major problems with sound systems of the time was the dynamic range. Film soundtracks typically had a very poor signal to noise ratio of about 40dB. In Fantasound, this was dealt with by increasing the volume during loud passages and reducing it during quiet sections. The result was effectively a wider dynamic range. The gain adjustment was facilitated with a tone-operated gain adjusting device, or “Togad”. It worked by changing the volume based on a tone of varying amplitude. 

After significant development and experimentation with a variety of speaker configurations, the final configuration of seven speakers and three source channels was decided on. This consisted of three speakers across the front, consisting of left, centre and right, along with two sets of surround speakers. In order to move the three channels between the speakers, a system was developed that allowed the sound to travel using constant fades. This circuit was the first panoramic potentiometer, or pan pot.

Fantasia debuted at the New York Theatre in New York City on November 13th, 1940. The film required the installation of the custom Fantasound system, which was very costly and time consuming to install. Consequently, Fantasound never expanded beyond the initial screenings of Fantasia and was abandoned shortly afterwards.

Quadraphonic

The roots of quadraphonic sound can be traced as far back as the 1950’s when a short lived four channel sound system briefly existed for use in FM broadcasting. Quadraphonic, as the name suggests, uses four channels, with a speaker arrangement not dissimilar to that of Fantasound. It wasn’t until the 1970s though, when it became widely available for consumers, with quad vinyl and reel to reel tape formats. The majority of releases were matrix encoded, with the four channels being encoded down to two channels for storage on the delivery medium. On playback, the sound output was passed through a decoder and routed to four speakers. The matrix encoded quad releases were backwards compatible with conventional two channel stereo playback. Some discrete versions of the quadraphonic format existed, including Quadradisc, which was the only discrete quad record format to gain widespread industry acceptance. 

Quadraphonic brought surround sound to the home, with the majority of releases being albums. Notable artists releasing albums in quad included Mott The Hoople, Black Sabbath, Alice Cooper, Bob Dylan, Pink Floyd, Simon and Garfunkel and Mike Oldfield.

Sensurround

In 1974, Cerwin-Vega in conjunction with Universal Studios developed a format called Sensurround. First used for screenings of the film Earthquake, Sensurround involved the installation of large, low frequency, horn-loaded speakers which contained specially designed 18-inch Cerwin-Vega Model 189 ES drivers in custom black wood cabinets. Sensurround’s selling point was that it added considerable low frequency extension for sound effects. At the time, there was no way to record frequencies lower than about 40Hz on an optical or magnetic film soundtrack. To get around this, a low frequency control track was used. This was printed onto the film’s mono optical or magnetic soundtrack. The output from this track was fed into a control box which then fed low frequency pseudorandom noise to 1600 watt amplifiers driving the speakers.

Due to the high installation cost, the amount of space the speakers required and some structural damage to cinemas due to the high playback level of very low frequency sound, Sensurround didn’t last long. Subsequent to Earthquake, it was used on a few other features, including Midway in 1976, Rollercoaster in 1977 and a handful of other titles including a limited 70mm release of Alien in 1979.

Dolby Stereo 70mm 6 track

In 1976 Dolby introduced a noise reduction system designed for six track 70mm film prints. In this system, the speaker configuration from a previous 70mm sound format dating back to 1955 from Todd-AO was repurposed. In the Todd-AO format, five speakers were used for the front channels, consisting of left, left centre, centre, right centre and right. A single mono surround channel was used with this. By the 1970s, an LCR configuration had become commonplace for the front channels, making the left centre and right centre channels redundant. Dolby repurposed these channels and speakers by instead using them for low frequency effects. The mono surround channel was retained in the initial version of Dolby Stereo 70mm six track. In a later revision, the unused high frequency capacity of those channels was used to provide for stereo surround in place of the mono surround of the Todd-AO layout. The Dolby Stereo 70mm six track format established for the first time the speaker configuration which would ultimately be retained by Dolby Digital. A notable movie release which utilised the Dolby Stereo 70mm six track sound format was Apocalypse Now in 1979.

Periphonic

This one isn’t a format as such but a collective term for any system which is capable of three dimensional sound reproduction in both the horizontal and vertical planes. This is done by employing height channels, as well as the usual surrounds. There have been a few experimental formats over the years which have employed this kind of setup, none of which gained much traction until the introduction of Dolby Atmos. Back in the 1990s though, Yamaha incorporated provision for height channels in many of their home A/V receivers. This was a proprietary decoding technology which derived height channels from the de-correlated information in a conventional stereo or surround mix. A similar scheme was later employed by Dolby with Pro Logic IIz, which was again capable of decoding height information and routing it to speakers mounted above the listener, usually up high on the front wall. Although these formats did not provide true discrete height channels, the idea of utilising speakers above the listener in order to make the listening experience more immersive was nevertheless a good one, and this was to be developed further years later.

Dolby Digital

Starting life as Dolby Stereo Digital in 1986 and eventually becoming Dolby Digital in 1995, this lossy compression technology allowed 5.1 surround sound to be stored digitally on 35mm film prints. Also known as Dolby AC-3, Dolby Digital soundtracks were optically recorded as sequential data blocks between the sprocket holes down the edge of the film print. The first film to be released using this compression scheme was Batman Returns in 1992. 

Dolby Digital gained widespread acceptance, eventually being used for TV broadcasts, games consoles, DVD and Blu-ray Discs. Dolby Digital supports bit rates up to 640kbps. A later, revised version of Dolby Digital called Dolby Digital Plus allows for bit rates up to 6.144 Mbit/s and up to 15.1 discrete channels.

SDDS

Sony Dynamic Digital sound (SDDS) was introduced in 1993. Compressed digital sound was stored on both outer edges of 35mm film prints. Up to eight channels of sound were supported, with five across the front, two surrounds and a single sub-bass channel. The SDDS speaker configuration is not dissimilar to the old Todd-AO format, only with stereo surrounds and a dedicated sub channel.

Over 1,400 films were released in SDDS, although only 97 of these actually utilised all eight channels. SDDS was costly to install and was much less popular than DTS or Dolby Digital, due in part to its reliability issues. Because of the location of the SDDS audio tracks at the outer extremities of the 35mm print, it was prone to damage which could result in drop outs. To somewhat mitigate this, the data on the two sides of the film were offset by 17 frames, reducing the likelihood of a total dropout. Nevertheless, it was problematic and costly enough for the format to never gain the same widespread adoption as its rivals.

SDDS employed Sony’s ATRAC compression algorithm (yes, the same one used in MiniDisc), usually with a compression ratio of about 5:1 at a sample rate of 44.1kHz. The final SDDS releases were in 2007.

DTS

It would be wrong to talk about surround formats without mentioning Digital Theatre Systems. In 1993 they introduced their own digital audio codec to cinemas, rivalling Dolby Digital. There are various technical considerations when storing digital audio information on film, one of which is bit rate. There’s only a limited amount of space to actually put the audio, and by the time Digital Theatre Systems introduced their DTS system in 1993, almost all of the space had been taken up by other sound formats. Looking at the edge of the 35mm film print below, we can see the SDDS track on the left hand side, Dolby Digital between the perforations and the optical analog soundtrack near the right hand side. Look closely and you’ll see a series of white dashes next to this. This is a DTS timecode track. DTS worked by running the film along with a separate CD ROM player which ran in sync with the film print’s timecode track. The CD contained 5.1 audio encoded with DTS. As with Dolby Digital, DTS is a lossy codec which reduces the data rate of the audio. DTS was able to utilise higher bit rates than Dolby Digital, up to 1.5 MBit/s. The first film released in cinemas with DTS sound was Jurassic Park.

Dolby True HD and DTS-HD Master Audio

With the advent of Blu Ray and the now obsolete HD-DVD, the increased storage capacity over previous formats such as DVD meant that audio bit rates could be increased. Dolby developed a lossless compression system called Dolby True HD. This uses Meridian Lossless Packing (MLP) to minimise the data rate of the original uncompressed PCM audio in a way which can be reconstructed bit for bit on playback. The Dolby True HD specification allows for up to 16 channels and sample rates up to 192kHz at bit depths up to 24 bit.

Similarly, DTS developed their own lossless format called DTS-HD Master Audio. It supports up to eight channels of audio at bit depths up to 24 bit. For 6.1 and 7.1 sound, sample rates up to 96kHz are supported. For lower channel counts, sample rates can go up to 192kHz.

Object Based Audio

Object based audio first came to prominence with the release of Dolby Atmos in 2012. Rather than every sound being mixed to fixed channels, a proportion of the individual sound sources within a mix can be designated as objects. These audio objects are typically mono and have accompanying metadata which defines spatial position in X, Y and Z axes. Unlike conventional channel based formats, object based audio is inherently scalable to different numbers of speakers since the panning of sounds is not tied to particular channels but is defined by its positional coordinates. In addition to Dolby Atmos, other formats which incorporate object based audio include DTS: X and Auro-CX.

Dolby Atmos

Several surround formats are in common usage today. A good proportion of content is still mixed in 5.1 or 7.1 but increasingly, Dolby Atmos has found its way into movies, music and TV shows on streaming platforms. It is by far the dominant immersive audio format in use today. As mentioned in the ‘object based audio’ section above, Dolby Atmos is scalable. A common speaker configuration for mixing is 7.1.4 which provides a conventional 7.1 layout with the addition of 4 height channels. A Dolby Atmos mix includes up to 128 audio tracks - a 9.1 channel based ‘bed’ and up to 118 audio objects. When we consider the surround formats and innovations of the past, Dolby Atmos was almost an inevitability in that it brings together the best of the historical developments in surround sound and builds on it with the addition of object based audio.

For Walt Disney Pictures' 2016 film version of The Jungle Book, director Jon Favreau and composer John Debney sought to recreate the Fantasound experience Disney had in mind. When mixing the soundtrack in Dolby Atmos, as Favreau said, "we isolated instruments when we could. And in the sound mix, we created a Fantasound mix. If you see the film in Atmos, you will feel that there are instruments that move around the theater." A mention for Fantasound appears in the film's closing credits.

Sensurround and then Dolby Stereo 70mm six track, with their use of dedicated bass channels could be thought of as the precursors to what would eventually become the LFE channel, something which came into widespread use in 5.1 and then 7.1 and which still exists in Dolby Atmos.

Depending on the delivery platform, Dolby Atmos is encoded either losslessly with Dolby True HD or with their lossy Dolby Digital Plus codec. A Dolby Atmos mix on a Blu Ray or UHD Blu Ray disc is typically presented as a Dolby True HD stream, making it entirely lossless and identical in quality to what was heard on the substage. Due to bandwidth considerations on streaming platforms, Dolby Atmos from the likes of Netflix, Disney + and Amazon Prime is encoded with Dolby Digital + to keep the data rate down. It still sounds great though, and only the most astute home viewers are likely to pick up any audible difference between that and the lossless version.

Dolby Atmos’ use extends to games, with consoles such as the Xbox Series X providing an immersive sound experience for select content when played back through compatible equipment. The great news is, Atmos is scalable all the way down to playback over a pair of headphones, so it can still be experienced even if you don’t want to go to the length of installing speakers around the room and in the ceiling.

Final Thoughts

Hopefully this article has provided some interesting insight into some of the key technologies and developments which laid the groundwork for the formats of today, in particular Dolby Atmos. Numerous other surround formats have come and gone over the years but I believe we’ve touched on the most noteworthy ones which introduced innovations and ideas which were to persist and evolve over time, eventually coming together in the formats we enjoy today.