Dolby TrueHD is a lossless audio codec with support for up to 7.1 audio channels and is used with Blu-ray Discs. No major streaming platforms use it. Dolby Atmos is a 3D surround sound technology that allows sounds to be placed anywhere in a 3D environment. Dolby Atmos can be embedded inside of either Dolby TrueHD (lossless) or Dolby Digital Plus (lossy). In this article, we’ll discuss both Dolby TrueHD and Dolby Atmos in detail and help you understand how they differ yet work together at the same time.
Dolby TrueHD vs Dolby Atmos
Developed by the same company, Dolby Laboratories, these two audio formats work in completely different ways. You can consider Atmos to be an extension of Dolby’s TrueHD format. Therefore, when a sound device or TV does not support Dolby Atmos, the data is folded back into the bitstream in order to sustain backward compatibility. Typically, when a device is compatible with both of them, the Dolby Atmos gets higher priority than the Dolby True HD. In other words, if you play a movie with Atmos audio, your speaker set will decode the Atmos data and produce sound from it. However, if the device does not support Atmos, it ignores the extension data and plays the audio with Dolby TrueHD format.
What is Dolby TrueHD?
Dolby TrueHD, as mentioned before, is a lossless compression audio technology. That means there will be no noticeable difference in the quality of the sound after it’s decoded back into an uncompressed form. In short, the sound will be almost the same as when it was recorded. Usually, this type of sound format is used in Movie theaters. That is why we can notice even the faintest audio such as the blowing of wind or creaking of doors. The Dolby TrueHD audio codec can replicate sounds from different ranges. That’s why you can easily notice the varying intensity of the background music volume when watching movies in theaters. In short, this audio format retains every bit of data from its original file available before compression. This exponentially enhances the sound quality. However, it also makes the file size larger than lossy compression does, as seen in the Dolby Digital Plus compression.
What is Dolby Atmos?
Dolby Atmos is a surround-sound technology developed in 2012 that expanded the capabilities of the existing 5.1 and 7.1 channel configurations. What’s interesting is that Dolby Laboratories considers Atmos to be the most significant development since surround sound. Unlike set-ups with speakers along walls, Dolby Atmos offers an edge to the sound quality by adding height channels of audio. This includes both ceiling mounting speakers and speakers that bounce audio off of the ceiling. Dolby Atmos works out of a 3D environment. When movie and TV show audio engineers are adding audio to their content, they can have up to 128 discrete sounds playing throughout that 3D environment. They don’t have to choose each and every speaker that the audio plays from either, Dolby Atmos makes that decision for them. It fundamentally changes the way that movie and TV show producers look at audio and allows them to do so much more than ever before. Dolby Atmos is used in two different audio codecs, Dolby Digital Plus where it is compressed/lossy and Dolby TrueHD where it is uncompressed/lossless. Dolby Atmos cannot and will not work without using one of these audio codecs.
Does Dolby TrueHD Support Atmos?
Yes, Dolby TrueHD supports Dolby Atmos. This audio codec can work with up to 7.1 audio channels utilizing lossless compression. Not just that, it was designed especially for HD and UHD Blu-ray Discs. Also, the TrueHD format support for up to 24-bit audio is commendable. In addition, it offers a sampling rate ranging from 44.1 kHz to 192 kHz. The variable data rates are a result of its lossless compression. To be precise, the average bitrates for TrueHD sit around 6,000 kbps for Atmos at 48 kHz. However, the peak data rates can reach up to 18,000 kbps on multichannel content with a higher sampling rate. And while Dolby TrueHD itself supports up to 7.1 channels of audio, Dolby Atmos allows the audio to expand to far larger and more extensive channel configurations.
The Basics of Digital Sound and Audio Compression
We talked about sound formats and audio codecs. However, to understand these technologies a little better, it can help to understand a little bit about digital sound and audio compression.
What is a Digital Sound?
Natural sounds exist as waves and vibrations. However, digital sounds are different. Induced by gadgets made by humans, the effects we hear coming from devices aren’t natural. In other words, computers or speakers aren’t trained to process sound as we humans are. Therefore, we need ways to convert natural sound into digital formats that modern gadgets can understand. This is where digital audio technology comes in. The process involves the detection of natural sound waves and changing them into the computer language of binary data.
What is Audio Compression?
Contrary to digital sounds, audio compression helps in storing and transmitting digital audio between devices. Compression comes into play when we need to accommodate audio files within the limited space inside devices. As the name suggests, the process compresses audio files into smaller and more compact data sizes to make it convenient for devices to store them. After the transmission is completed, for instance, from a TV to an external speaker, these files are uncompressed to their original size. There are two different compression methods:
Lossy Compression
In this process, the audio file loses some data following decompression. Although the amount of data compromised is somewhat unnoticeable, it does affect the quality of the sound as compared to lossless compression.
Lossless Compression
Unlike lossy compression, there is no loss of data in lossless compression. After restoring data back through decompression, the file retains its original form. Therefore, the sound quality is much better than lossy compression.
