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Apple Details How HomePod Can Detect 'Hey Siri' From Across a Room, Even With Loud Music Playing

In a new entry in its Machine Learning Journal, Apple has detailed how Siri on the HomePod is designed to work in challenging usage scenarios, such as during loud music playback, when the user is far away from the HomePod, or when there are other active sound sources in a room, such as a TV or household appliances.


An overview of the task:
The typical audio environment for HomePod has many challenges — echo, reverberation, and noise. Unlike Siri on iPhone, which operates close to the user’s mouth, Siri on HomePod must work well in a far-field setting. Users want to invoke Siri from many locations, like the couch or the kitchen, without regard to where HomePod sits. A complete online system, which addresses all of the environmental issues that HomePod can experience, requires a tight integration of various multichannel signal processing technologies.
To accomplish this, Apple says its audio software engineering and Siri speech teams developed a multichannel signal processing system for the HomePod that uses machine learning algorithms to remove echo and background noise and to separate simultaneous sound sources to eliminate interfering speech.

Apple says the system uses the HomePod's six microphones and is powered continuously by its Apple A8 chip, including when the HomePod is run in its lowest power state to save energy. The multichannel filtering constantly adapts to changing noise conditions and moving talkers, according to the journal entry.

Apple goes on to provide a very technical overview of how the HomePod mitigates echo, reverberation, and noise, which we've put into layman's terms:
  • Echo Cancellation: Since the speakers are close to the microphones on the HomePod, music playback can be significantly louder than a user's "Hey Siri" voice command at the microphone positions, especially when the user is far away from the HomePod. To combat the resulting echo, Siri on HomePod implements a multichannel echo cancellation algorithm.
  • Reverberation Removal: As the user saying "Hey Siri" moves further away from the HomePod, multiple reflections from the room create reverberation tails that decrease the quality and intelligibility of the voice command. To combat this, Siri on the HomePod continuously monitors the room characteristics and removes the late reverberation while preserving the direct and early reflection components in the microphone signals.
  • Noise Reduction: Far-field speech is typically contaminated by noise from home appliances, HVAC systems, outdoor sounds entering through windows, and so forth. To combat this, the HomePod uses state-of-the-art speech enhancement methods that create a fixed filter for every utterance.
Apple says it tested the HomePod's multichannel signal processing system in several acoustic conditions, including music and podcast playback at different levels, continuous background noise such as conversation and rain, noises from household appliances such as a vacuum cleaner, hairdryer, and microwave.

During its testing, Apple varied the locations of the HomePod and its test subjects to cover different use cases. For example, in living room or kitchen environments, the HomePod was placed against the wall and in the middle of the room.

Apple's article concludes with a summary of Siri performance metrics on the HomePod, with graphs showing that Apple's multichannel signal processing system led to improved accuracy and fewer errors. Those interested in learning more can read the full entry on Apple's Machine Learning Journal.

Related Roundup: HomePod
Buyer's Guide: HomePod (Neutral)


Top Rated Comments

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1 week ago
Hey Apple, just do me a favour and fix "Hey Siri" on iPhones. Works 1 out of 10 times.
Rating: 26 Votes
1 week ago
It occurs to me that as the prospective release date of Hey-Siri-enabled AirPods gets pushed further and further back, folks can work out a temporary solution by simply attaching two HomePods to their ears.

Rating: 14 Votes
1 week ago

My Echo Dots do this, and they cost £25 each.....


I have multiple dots, regulars echos, echo show's etc. (10 Alexa devices total) and 3 google home devices. I can tell you that while they are better than almost everything involving voice and crush Siri, this is the one place where Homepod absolutely SMOKES them. There is zero contest. It is not at all what you are thinking, The Homepod is much louder than those other devices and even at full volume, I can speak in a normal voice without shouting over the music and it work every time. It is the best part of the Homepod and Apple nailed this part. This part really seems like magic by comparison.
Rating: 14 Votes
1 week ago

Hey Apple, just do me a favour and fix "Hey Siri" on iPhones. Works 1 out of 10 times.

Works like 99 out of 100 times for me. Maybe try setting it up again.
Rating: 14 Votes
1 week ago
My Echo Dots do this, and they cost £25 each.....
Rating: 12 Votes
1 week ago

Sounds physically impossible what You say. Only possible when they filter the output of the voice frequencies from the music. Even then how should it hear You from far away when there’s loud music?
But then it is an inferior speaker, all very strange info around HomePod,from You fanboys


"Only possible when they filter the output of the voice frequencies from the music."

Nope. You might not be aware that there are voice frequencies within music. Voice and music both occupy the range of audio frequencies.


"Even then how should it hear You from far away when there’s loud music?"

Signal processing, cancelling output music from the microphone's input, and adaptive beam-forming. Easy. And it works so well.


"But then it is an inferior speaker, all very strange info around HomePod"

You might want to understand the technology and signal processing before making such a comment.
Rating: 10 Votes
1 week ago
This might be one of the most impressive aspects of the HomePod, much better than my Echo's ever were. I can be almost anywhere in my house (2,400 square feet) and either my upstairs or downstairs HomePod will hear me perfectly.
Rating: 10 Votes
1 week ago

Hey Apple, just do me a favour and fix "Hey Siri" on iPhones. Works 1 out of 10 times.

You might need to disable the feature and then re-enable it so it runs you through the routine of training it to recognize your voice.

My wife's iPhone recognizes her saying "Hey Siri" and mine recognizes me even when we are both in the same room with our phones next to each other on the coffee table.
Rating: 6 Votes
1 week ago

tl;dr its got creepy sound isolation intelligence, like HAL9000

Lip reading feature coming soon to Facebook's Portal.
Rating: 6 Votes
1 week ago

Unless someone knows a simple way to mute a Homepod???


"Hey Siri stop."
Rating: 5 Votes

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