Audio codecs – your soundtrack!
January 19, 2024“Presented in Dolby Digital“ or “Dolby Surround“ – we all know this technical movie information from cinemas and DVD. But what does this mean and how do audio codecs determine the Dolby standards? In this blog post, we hand you some basic facts about Dolby specifications, audio codecs, some typical issues and solutions. We’ll also take a short trip to audio standards and codecs applied with XR and VR video content.
What does “Dolby“ want to tell us?
Everyone knows Dolby standards from different media contexts. However, not everyone knows their name and innovation comes from Dolby Laboratories, a US-based audiovisual media company with locations and customers all over the world. Dolby has been there for decades, even since the times when radio and cassettes were still the pinnacle of technology. Some of the best-known audio solutions are Dolby Noise Reduction and Dolby Surround (first applied in the 1960s and 1970s), Dolby Digital (1990s) and Dolby Atmos (2012). Let’s check on some basic features of Dolby formats before moving on to audio codecs in detail!
Dolby Noise Reduction (DN)
Dolby Noise Reduction is an analog system which served to reduce background noise in analog audio recordings.It was usually applied with early analog media like cassette tapes and thus doesn’t include any common digital codecs.
Dolby Surround
Dolby Surround was one of the earliest attempts at multichannel audio for film. It utilized four channels of audio (left, center, right, and a mono surround channel) to create a more immersive experience. In practice, people mainly found it in movie theaters, in VHS tapes and in laser discs.
Dolby Pro Logic and Dolby Pro Logic II
In the context of home theater and surround sound, Dolby Pro Logic and Dolby Pro Logic II are examples of matrix encoding systems that fall under the Dolby Surround umbrella. These systems take stereo audio signals and use matrix encoding to create additional surround sound channels.
Admittedly, Dolby Pro Logic and Dolby Pro Logic II are not „real“ codecs in the traditional sense. Instead, they are decoding technologies that work in conjunction with audio codecs to create a surround sound experience from stereo sources. The actual audio codecs used for Dolby Surround content can vary and may include Dolby Digital (AC-3) for DVDs or Dolby Digital Plus for streaming services.
Dolby Pro Logic
Pro Logic belongs to the earlier Dolby Surround systems and is commonly used to decode surround sound from stereo sources. It typically involves a front left, front center, front right, and a mono rear channel.
Dolby Pro Logic II
As a successor version of Dolby Pro Logic, Dolby Pro Logic II is designed to provide a more immersive surround sound experience. It can decode stereo signals into 5.1 or 7.1 channel surround sound. This is because the system includes sound signals front left, front center, front right, rear left, rear right, and a subwoofer channel.
Dolby Digital
Dolby Digital is a digital audio coding technique that significantly improved sound quality by employing up to 5.1 channels (front left, front center, front right, rear left, rear right, and a low-frequency effects channel) of surround sound. Due to its high-quality audio and compression efficiency, this audio format became the “golden standard“ for DVDs, digital TV, Blu-rays, and many other digital media platforms. Alt least before newer formats took over.
Dolby Atmos
Dolby Atmos revolutionized audio by introducing object-based audio. Unlike traditional channel-based audio, Atmos treats sounds as individual objects in a 3D space, allowing for more precise placement and movement of audio elements. First, film makers used this format mainly in movie theaters. Later, Atmos expanded to home theaters, soundbars, headphones, and mobile devices. Overall, this sound system offers an immersive audio experience with overhead and multidimensional sound.
Dolby TrueHD
Dolby TrueHD is a lossless audio standard (with a matching codec). You’ll mainly find it in Blu-ray discs. One of the this standard’s advantages: It provides high-fidelity audio and supports up to 7.1 channels of surround sound. TrueHD offers studio-quality audio without any compression, delivering an immersive audio experience. The downside: All lossless video and audio formats demand a higher storage capacity and bitrate than their compressed counterparts.
Dolby Digital Plus
Dolby Digital Plus, also: Enhanced AC-3 or E-AC-3, is the “Hollywood glam“ version of Dolby Digital. This is because Dolby Digital Plus supports higher bitrates, more channels (up to 13.1), and improved efficiency. Meanwhile, this standard (and matching codec) maintain backward compatibility with Dolby Digital. Film makers commonly use this standard for streaming services and some Blu-ray discs.
Understanding audio codecs
There are matching audio codecs for each standard and purpose. Depending on what you want to use your video files for, you should also select an audio fornat matching technical resources (bandwidth, storage, degree of compression) and target audience. For example, a highly compressed codec lowering sound quality to a certain degree might work perfectly for your Instagram reels. In contrary, you should rely on high-quality and maybe even lossless formats to offer your videos on TV or in a movie theatre or on streaming platforms. In the following overview, you’ll find some common examples of frequently used audio codecs.
MP3 (MPEG-1 Audio Layer III) – the compact “allrounder“ for all occasions
Facts in a nutshell:
MP3 (MPEG-1 Audio Layer III)is a highly compressed audio format. Its main advantage compared to lower-compressed codecs: MP3 content runs easily on every output device no matter how „big“ or „small“ the RAM or storage capacity. Furthermore, MP3 files are small, “compact“ and enjoy a widespread support network.
Performance issues
Due to heavy compression, your audio quality might decrease.
Boosting your sound experience
For a richer sound experience, higher bitrates can be a gamechanger. As an alternative, conversion is key – meaning conversion to lossless formats like FLAC.
AAC (Advanced Audio Coding) – efficient, but a little “picky“
Facts in a nutshell
Compared to MP3, the AAC codec generelly is a more efficient match. Its compression level is lower so you often get a more splendid sound experience. Originally, this codec was developed for iTunes and Apple devices.
Performance issues
Non-Apple devices and older media players might not fully support the AAC format.
Boosting your sound experience
You want to make sure that you always get the full portion of sound? Then convert AAC files to MP3 for broader compatibility or use media players that support AAC!
AC-3 and E-AC-3 – the “blockbuster“ codecs
Facts in a nutshell
AC-3 is closely linked to the common Dolby Digital audio standard, thus it was created for the bigger screen (TV, DVD, cinema, partially streaming, Blu-ray). This versatile audio codec supports multiple audio channels, typically up to 5.1 channels, providing a surround sound experience. As a supreme audio format, AC-3 uses perceptual audio coding to achieve high compression ratios without a significant loss of audio quality. It further employs psychoacoustic modeling to discard audio data that is less likely to be perceptible to the human ear.
AC-3 supports a range of bitrates, allowing flexibility in audio quality. Higher bitrates generally result in better audio fidelity but require more storage or bandwidth. AC-3 has become a standard audio format for DVDs, providing a balance between audio quality and file size. The best-known and newest AC-3 extension is Dolby Digital Plus (E-AC-3).
Performance issues
When editing and playing AC-3 and E-AC-3 tracks, occasional dropouts or distortion in the audio stream can occur. This widespread issues can naturally also be caused by file defects or data loss which need recovery or repair. In some cases, the audio and video are not in sync. This issue then leads to a mismatch between what you see and hear. For sure, you might also encounter playback devices and media players which do not support the AC-3 codec or its variations. Depending on recording and playback settings, sometimes the audio quality is lower than expected. The correct encoding settings for AC-3 files are also crucial for success because improper configuration settings can lead to all issues mentioned above.
Boosting your sound experience
For all issues, the source file is the first factor to check on as it might have been hit by file corruption and the video needs repair. In case the file doesn’t show any defects but the issue persists, you playback device or software is the next aspect you should analyze and fix. In fact, you should always keep your player, receiver and software up to date. Alternatively, you can also rely on a different media player or playback device.
Some playback devices and media players just were not designed to play AC-3 or E-AC-3 audio tracks. In this case convert the AC-3 file to a more widely supported format but always save the original file. In order to optimize audio quality, check the bitrate of the AC-3 file. Higher bitrates generally result in better audio quality. Last and least, the quality of the source file set the boundaries of what’s possible.
Audio codecs for Virtual and Extended Reality
While everyone relies on videos in many aspects of life, VR, XR, AR and MR still require special video and audio codecs besides the well-known ones we presented above. So let’s take the chance here and check on some basic facts on VR and XR standards.
VR (Virtual Reality)
Audio standards for VR settings
- Ambisonics: Ambisonics is a standard for representing 360-degree sound environments. Above all, it captures audio from all directions,. Thus, Ambisonics enables users to experience immersive audio that changes based on their orientation within the VR environment.
- Binaural Audio: This audio standard simulates the natural hearing experience by using two microphones to create a 3D stereo sound . Thus, it is able to replicate how humans perceive sound direction and distance.
Matching audio codecs
- AAC (Advanced Audio Coding): AAC is a widely used codec for encoding high-quality audio. In a VR context, content creators often rely on it to deliver spatial audio in VR applications. This is because AAC highly supports multichannel audio files while providing a high level of efficiency and compression.
XR (Extended Reality)
Audio standards for XR settings
- Spatial Audio: Similar to VR, spatial audio techniques like Ambisonics and binaural audio are crucial in XR settings. More precisely, they enable the placement of sound sources in a 3D space. In consequence, spatial audio standards have the power to enhance the immersive feel of the environment.
Matching audio codecs
- Opus: Without a doubt, there are lot of audio codecs to choose from in XR. However, many video creators trust in Opus as a versatile codec that supports low-latency encoding and decoding of audio. Furthermore, Opus is suitable for delivering high-quality audio in real-time for XR applications.
MR (Mixed Reality) and AR (Augmented Reality)
Audio Standards for MR and AR settings
- Spatial Audio: As in VR and XR, spatial audio remains crucial in MR and AR to create realistic auditory experiences that align with the visual elements. For sure, this also requires the multidimensional perception of audio coming from specific locations in the user’s environment. Depending on the output device, content creators can also use standard formats like Dolby Atmos, Dolby Digital and Dolby Digital Plus.
Matching audio codecs
- Dolby Atmos for headphones: In general, MR content requires special headphones. For this device, Dolby Atmos is a leading technology in order to create immersive audio experiences in AR/MR applications. It does not only provide object-based audio, but also provides precise sound placement and movement in the virtual or augmented space.
In a nutshell, content developers often rely on these standards and codecs in order to create immersive and realistic audio experiences in virtual, augmented, mixed, and extended reality applications. All these technical tools and details play a significant role in enhancing the overall immersion and sense of presence within these environments. More precisely, they provide spatially accurate and high-quality audio cues which fascinate and entertain all users of this highly complex video content. Last and least, keep in mind that technology is always in a flow. So, you can be sure that also video and audio codecs will be changing at times. Whatever you need it for – we wish you all the best with your perfect movie soundtrack.
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