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Except it doesn't send any data to the cloud. They mentioned that explicitly. There's an on-phone database of songs that it is matching against.

I wonder how much space this takes on the device. How many signatures does it keep and how often is this updated

It's not very significant. Basically it stores some distances between peaks in each song's spectrogram which can then be further compressed.

Even supporting a database of millions of songs would be possible.

Spotify has 30 million songs.

Even if it takes up a small amount of space, it's basically a non-feature.

The index can be highly compressed, see for example

>Spotify has 30 million songs.

Many of those songs have never been played[1]. There's a really (really, really, really) long tail.

If each signature occupies an effective space of 1k (not sure how feasible this is), then for 1000 songs this would take 1M, 10M for 10k songs, etc

Every year gives us around 100 popular songs (add a % of location-specific popular ones), so it seems the plan is feasible.

> They mentioned that explicitly

Okay? The submitted article certainly didn't mention that.

The Anadtech live blog does indeed state "01:05PM EDT - On device machine learning. Local music identificat (sic)"