Why HomePod’s ‘Hey Siri’ will blow you away


Siri speaker
The HomePod's ability to hear at full volume is one of the most impressive feats.
Photo: Ste Smith/Cult of Mac

Apple pulled back the curtain on some of the most complicated features of its HomePod smart speaker this morning with a new blog post that details the machine learning tech that goes into its ‘Hey Siri’ detection.

One of the biggest challenges with making a smart speaker is not only figuring out what to listen for but also what sounds to discard in the process. Apple’s engineers have come up with a number of interesting methods to make Siri work even when you’re blasting tunes our of the HomePod’s speakers.

In its new machine learning blog post, Apple’s team explains that bringing Siri to HomePod is much more challenging than on iPhone because the user is giving commands to the microphone from a much farther distance. Echo, reverberation, and noise are the biggest hurdles for Siri in a far-field setting because users want to trigger Siri from the couch or kitchen and don’t care where HomePod is located.

Apple uses a multichannel signal processing system to ensure Siri recognizes and responds to all commands. The company says it uses two approaches to make this happen: 1) Mask-based multichannel filtering using deep learning to remove echo and background noise, 2) Unsupervised learning to separate simultaneous sound sources and trigger-phrase based stream selection to eliminate interfering speech.

Powered by Apple’s A8 chip and six microphones, HomePod is able to continuously listen for commands even in its lowest power state. The filtering algorithms constantly adapt to noise conditions, the state of the physical state of the room, and moving talkers.

The amount of detail that has to go into multichannel echo cancellation, mask-based echo suppression, reverberation removal and mask-based noise reduction is truly astounding for a feature most users don’t even think twice about. Often times when in use, the HomePod’s speakers are so loud they drown out voice commands from across the room. With its multichannel signal processing system, Apple’s been able to increase Siri’s accuracy with fewer errors, leading to an overall improved experience.

If you’re interested in all the details on how Apple makes Siri work like magic on HomePod, check out the full blog post on its site. The company included graphs and equations on some of the smallest details.