From the very early days, Dolby has been working on delivering high-quality audio by preserving the integrity and the authenticity of the sound recorded. With this mission in mind, Dolby has been developing technologies across the entire audio delivery chain for production, broadcasting, and playback.
When Dolby started in cinema, the thought of bringing surround sound into the home seemed outlandish. Then we did it. We brought great sound to even smaller spaces with our products for PCs. Now, we’re taking the next step and bringing big sound to the smallest devices yet, smartphones and tablets.
The challenge with mobile entertainment comes from both the device’s form factor and the variation in quality of the digital content available (Ed.: you can read more about this issue here.)
In this post, let’s review how Dolby professionals optimize the hardware with technologies that compensate for the deficiencies of tiny, built-in portable speakers.
Dolby has developed three main technologies that interact to optimize speaker playback:
- The Audio Optimizer, which compensates for the audio limitations of the playback system
- The Volume Maximizer, which intelligently boosts the volume level
- And the Audio Regulator, which enables an optimum listening experience by preventing distortion
The Audio Optimizer is the result of the device’s playback system tuning. Dolby professionals analyze the frequency-response of the speakers and identify any deficiencies that can be compensated for with proprietary audio correction filters. These reestablish the lost highs and lows, which result in sound that feels more natural, more balanced, and truer to the way its creator meant it to be heard.
The Volume Maximizer is an intelligent and powerful volume-level boost. It ensures that the audio coming from small mobile speakers is consistently loud. In the process, certain parts of the signal may exceed the amplitude limits inherent to the audio signal’s digital representation, causing clipping. To eliminate any chance of the listener experiencing distortion, while maintaining the desired boost in loudness, the Volume Maximizer employs a high-quality, look-ahead signal peak limiter to prevent clipping.
What does that mean? Well, it’s a little bit like if a celebrity was walking through a crowded room with a handful of bodyguards. Those bodyguards would be on the lookout for overeager fans trying to get too close to their favorite celebrity, and the bodyguards would anticipate and address those fans to make sure that the celebrity never had to deal with them.
The Volume Maximizer is the bodyguard that lets you keep the party as loud as you want it without worrying about overeager peaks coming in and adding harshness to your listening experience. This technology intelligently combines with the Audio Regulator, which prevents distortion at a more global level.
The nature of the distortion in mobile devices is highly irregular. The components of the audio signal chain and the mechanical characteristics of the device all contribute to the distortion. For example, underpowered amplifiers combined with high-level signals may cause a portion of the chassis to rattle. Similar to the Audio Optimizer, the Audio Regulator requires a calibration procedure for each device’s model prior to production.
The procedure involves probing a multitude of frequency bands with a test signal and measuring the amount of distortion in each band as a function of the test signal’s level. Based on a maximum amount of allowable distortion, a limit is then set for each frequency band.
To extend the bodyguard metaphor, the Audio Regulator is like a bodyguard who has taken his client along this route before, and knows the places that he or she should avoid in advance. Even so, the Volume Maximizer is still around to deal with the unexpected riffraff that might pop up. As a result, the Audio regulator maintains high-volume levels signals distortion free.
With all three technologies interacting with each other in Dolby® Digital Plus™, the sound of mobile entertainment, ensures that HD sound-breaking audio sticks with you everywhere.