Introduction to Digital Cinema: Audio and Visual Formats

After discussing why distributors were eager to upgrade their entire eco-system in our previous blog; Converting an Industry, we'll be analysing the differences between audio and visual commonly used in cinema.

When a distributor sends out content, they have to provide variations that can result in each feature having hundreds of different versions. But first, let's start with the foundations of all those versions; the image and sound.

Aspect ratio vs. Resolution

Sometimes, resolutions and ratios are talked about as if they were interchangeable, but this is not the case. The resolution is the number of pixels that make up the image, whereas the ratio is the image's height in relation to its width.

In the past, filmmakers and studios experimented with different aspect ratios ranging from 4:3 all the way to Cinerama, which projected three 35mm prints onto a curved screen to create a single widescreen image. Before the industry settled on the two standards that are still in use today, filmmakers often filled the full frame and relied on projectionists to crop the image to the correct aspect ratio during projection.

Now, however, most content will be filmed and then shown at the cinema in either Flat or Scope, unless it is shown in a proprietary format, like IMAX.

Flat 1.85:1?Also known as Widescreen, but not to be confused with widescreen TVs, which run at a 1.77:1 ratio. The ratio means that if we had a screen that was 2 metres tall, it would need to be 3.7 metres wide to play Flat content.

Scope 2.39:1?Also known as Cinemascope or, more traditionally, Anamorphic. To achieve this on 35mm, filmmakers used an anamorphic lens, which squeezed double the width of image onto the film. Projectors were then fitted with a lens that stretched the image back out to the correct aspect ratio, which for 35mm was slightly different at 2.35:1 versus the digital ratio of 2.39:1. The current digital ratio means that if we had a screen that was 2 metres tall, it would need to be at least 4.78 metres wide to play Scope content. Resolution, on the other hand, refers to the number of pixels that make up the image.

2K is the generic term for images with a horizontal resolution of about 2000 pixels, and is the most commonly displayed resolution at digital cinemas.

4K is the generic term for images with a horizontal resolution of about 4000 pixels.

Masking

Masking is a border, usually a black curtain, around the cinema screen that can be adjusted based on the aspect ratio of the content being shown, and provided films shown in 35mm with crisp edges. Either curtains on both sides will turn a Scope screen into Flat, or a curtain will drop from the top of the screen to turn a Flat into Scope.

This allows the projected image to take up the full size of the screen for an immersive experience. Although digital projection provides perfectly clean edges on its own, if the image is not correctly masked, it can still be distracting for some audiences. For example, if a Scope image is letterboxed to fit onto a Flat screen, black bars on the top and bottom of the image are projected onto the screen to allow for the extra width. This can make it difficult to tell where the image ends in a dark scene, and can make the defining feature of Scope, its width, compete against Flat’s advantage; its height.

Surround Sound

Surround sound systems work by dividing the auditorium into discrete sound areas that each use their own sound channels. Each channel has its own uniquely mixed audio output, which is why sound at the cinema is so immersive. Dialogue comes right from characters' lips through the speaker centred behind the screen, and the footsteps of the villain gaining on them come from behind the audience, while the subwoofer produces the deep boom of an explosion that resonates within the whole room.

5.1?This is the most common surround sound set-up and creates five areas of sound- left, centre, right, left surround, and right surround .

7.1?7.1 surround sound further splits the two surround channels into left surround, back surround left, right surround, and back surround right.

Did you know??The .1 references the bass or LFE. In audio, LFE stands for Low-Frequency Effects. It is a band-limited audio track that is used for reproducing deep and intense low-frequency sounds in the 3–120 Hz frequency range. The .1 references the bass or LFE. In audio, LFE stands for Low-Frequency Effects. It is a band-limited audio track that is used for reproducing deep and intense low-frequency sounds in the 3–120 Hz frequency range.

Dolby Atmos

Dolby Atmos, Dolby's proprietary immersive sound solution, introduces the possibility of separate surround channels above the audience and has the potential to isolate up to 64 different speakers into different channels. It also allows sound engineers to forego channels entirely if they want to, to place sound 'objects' in a 3D space representing the auditorium.